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.ce 14
THE DESIGN AND IMPLEMENTATION
OF INGRES

by

MICHAEL STONEBRAKER, EUGENE WONG AND PETER KREPS
DEPARTMENT OF ELECTRICAL ENGINEERING AND COMPUTER SCIENCE
UNIVERSITY OF CALIFORNIA, BERKELEY, CA.

and

GERALD HELD
TANDEM COMPUTERS, INC.
CUPERTINO, CA.
.sp 5




ABSTRACT
.ce 0
.ph
This paper describes the CURRENTLY OPERATIONAL
version of the INGRES data base management system.
This multi-user system gives a relational view of
data, supports two high level non-procedural data
sublanguages and runs as a collection of user
processes on top of the UNIX operating system for
Digital Equipment Corporation PDP 11/40, 11/45 and 11/70
computers.
Stressed here are the design decisions and
tradeoffs related to 1) structuring the
system into processes, 2) embedding one
command language in a general purpose programming language,
3) the algorithms implemented to process interactions,
4) the access methods implemented 5) the concurrency
and recovery control provided 6) support for views, protection
and integrity constraints and 7) the data
structures used for system catalogs and role
of the data base administrator.
.bp
.fo 'DESIGN OF INGRES (I)'-%-'12/5/75'
1  INTRODUCTION

INGRES (Interactive Graphics and Retrieval System) is
a relational data base system which is 
implemented
on top of
the UNIX operating system developed at Bell Telephone
Laboratories [RITC74] for Digital Equipment
Corporation PDP 11/40, 11/45 and 11/70 computer systems.
The implementation of INGRES is primarily programmed in "C", a high
level language in which UNIX itself is written.  Parsing is done
with the assistance of YACC, a compiler-compiler available
on UNIX [JOHN74].

The advantages of a relational model for data
base management systems have been extensively discussed
in the literature, [CODD70,CODD74,DATE74] and hardly require further elaboration.
In choosing the relational model, we were particularly 
motivated by (a) the high degree of data independence that such
a model affords, and (b) the possibility
of providing a high level and entirely procedure-free
facility for data definition, retrieval, update, access
control, support of views, and integrity
verification.

In this paper we will describe the design decisions made in INGRES.
In particular, we will stress the design and implementation of:

.ss
a) the embedding of all INGRES commands in the general purpose 
programming language "C"

b) the access methods implemented

c) the catalog structure and the role of the data base
administrator

d) support for views, protection and integrity constraints

e) the decomposition procedure implemented

f) implementation of updates and consistency of secondary indices

g) recovery and concurrency control

.ds
Except where noted to the contrary, this paper describes the 
INGRES system operational in January, 1976.

To this end we first briefly describe in Section 1.2  
the primary query language supported, QUEL,
and the utility commands accepted by the current system.   
The second user interface, CUPID, is a graphics
oriented, casual user language which is also
operational and described in [MCDO75a, MCDO75b].
It will not be discussed further in this paper.
Then in Section
1.3 we describe the relevant factors in the UNIX environment which have affected our 
design decisions.

In Section 2 we discuss the structure of the four
processes (see Section 1.3 for a discussion of
this UNIX notion)
into which INGRES is divided and the reasoning behind the 
choice implemented.  The EQUEL (Embedded QUEL) precompiler, which allows the substitution of 
a user-supplied C program for the "front end" process is also 
discussed.
This program has the effect of embedding all
of INGRES in the general purpose
programming language "C".
Then in Section 3 we indicate the data structures which are implemented in
INGRES, the catalog (system) relations which exist and the role 
of the data base administrator with respect to all relations in a data base.
The implemented access methods, their calling conventions, and the
actual layout of data pages in secondary storage
where appropriate, are also presented.

Sections 4, 5 and 6 discuss respectively the various functions of each of the 
three "core" processes in the system.  Also discussed are the design and 
implementation strategy of each process.  Lastly, Section 7 draws 
conclusions, suggests future extensions and indicates the nature of the
current applications run on INGRES.

1.2 QUEL AND THE OTHER INGRES UTILITY COMMANDS

QUEL (QUEry Language) has points in common with Data Language/ALPHA
[CODD71], SQUARE
[BOYC73] and SEQUEL [CHAM74] in that it is a complete [CODD72] query language which frees the
programmer from concern for how data structures are implemented and what
algorithms are operating on stored data.  As such it facilitates a considerable
degree of data independence [STON74a].

The QUEL examples in this section all concern
the following relation.

.nf
.ne 7
            NAME     DEPT     SALARY      MANAGER      AGE
.ss

            Smith    toy      10000       Jones        25
EMPLOYEE    Jones    toy      15000       Johnson      32
            Adams    candy    12000       Baker        36
            Johnson  toy      14000       Harding      29
            Baker    admin    20000       Harding      47
            Harding  admin    40000       none         58
.ds
.fi

Indicated here is an EMPLOYEE relation with domains NAME, DEPT, SALARY,
MANAGER and AGE.  Each employee has a manager (except for Harding who
is presumably the company president), a salary, an age, and is in a department.

A QUEL interaction includes at least one RANGE statement of the form:

 	RANGE OF variable-list IS relation-name

The symbols declared in the range statement are variables which will be used 
as arguments for tuples.  These are called TUPLE VARIABLES.  The purpose
of this statement is to specify the relation over which each variable ranges.

Moreover, an interaction includes one or more statements of the form:

	Command [Result-name] ( Target-list )
		[ WHERE Qualification ]

Here, Command is either RETRIEVE, APPEND, REPLACE,
or DELETE.
For RETRIEVE and APPEND,
Result-name is the name of the relation which qualifying tuples
will be retrieved into or appended to.
For REPLACE and DELETE, Result-name is the name of a tuple variable
which, through the qualification, identifies tuples to be modified or
deleted.
The Target-list is a list of the form

	Result-domain = Function ...

Here, the Result-domain's are domain names in the result relation
which are to be assigned the value of the corresponding
function.

The following suggest valid QUEL interactions.  A complete description of the
language is presented in [HELD75a].

Example 1.1     Find the birth year of employee Jones

.ss
	RANGE OF E IS EMPLOYEE
	RETRIEVE INTO W (BYEAR = 1975 - E.AGE)
	WHERE E.NAME = "Jones"
.ds

Here, E is a tuple variable which ranges over the EMPLOYEE relation and all tuples
in that relation are found which satisfy the qualification E.NAME = "Jones".
The result of the query is a new relation, W, which has a single domain,
BYEAR, that has been calculated for each qualifying tuple.
If the result relation is omitted, qualifying tuples are 
written in display format on the user's
terminal or returned to a calling
program in a prescribed format as discussed in Section 2.
Also, in the Target-list, the "Result-domain =" may be omitted
if Function is the right hand side is an existing domain (i.e. NAME = E.NAME may
be written as E.NAME -- see example 1.6).

Example 1.2    Insert the tuple (Jackson,candy,13000,Baker,30) into EMPLOYEE.

.ss
	APPEND TO EMPLOYEE(NAME = "Jackson", DEPT = "candy",
		SALARY = 13000, MGR = "Baker", AGE = 30)
.ds

Here, the result relation EMPLOYEE is modified by adding the indicated tuple
to the relation.  
If not all domains are specified,
the remainder default to zero for numeric domains
and null for character strings.

Example 1.3    If a second relation DEPT(DEPT, FLOOR#) contains
the floor# of each department that an
employee might work in, then one can fire
everybody on the first floor as follows:

.ss
	RANGE OF E IS EMPLOYEE
	RANGE OF D IS DEPT
	DELETE E WHERE   E.DEPT = D.DEPT 
		     AND  D.FLOOR# = 1
.ds

Here E specifies that the EMPLOYEE relation is to be modified.
All tuples are to be removed which have a value for DEPT
which is the same as some department of the first floor.

Example 1.4    Give a 10 percent raise to Jones if he works on the first floor

.ss

	RANGE OF E IS EMPLOYEE
	RANGE of D is DEPT
	REPLACE E(SALARY BY 1.1 * E.SALARY)
	WHERE E.NAME = "Jones" AND
              E.DEPT = D.DEPT AND D.FLOOR# = 1

.ds

Here, E.SALARY is to be replaced by 1.1*E.SALARY for those tuples in EMPLOYEE
where the qualification is true.
(Note that the keywords IS and BY may be used interchangeably with "=" in
any QUEL statement.)

Also, QUEL contains aggregation operators including COUNT, SUM, MAX, MIN,
and AVG.
Two examples of the use of aggregation follow.

Example 1.5    Replace the salary of all toy department employees by the average
toy department salary.

.ss
	RANGE OF E IS EMPLOYEE
	REPLACE E(SALARY BY AVG(E.SALARY WHERE E.DEPT = "toy") )
		WHERE E.DEPT = "toy"
.ds

Here, AVG is to be taken of the salary domain for those tuples satisfying 
the qualification E.DEPT = "toy".  Note that AVG(E.SALARY WHERE E.DEPT= "toy") is
scalar valued (in this instance, $13,000)
and consequently will be called an AGGREGATE.  More general 
aggregations are possible as suggested by the following example.

Example 1.6     Find those departments whose average salary exceeds the company
wide average salary, both averages to be taken only for those
employees whose salary exceeds $10000.

.ss
	RANGE OF E IS EMPLOYEE
	RETRIEVE INTO HIGHPAY (E.DEPT)
	WHERE 	AVG(E.SALARY BY E.DEPT WHERE E.SALARY > 10000)
		>
		AVG(E.SALARY WHERE E.SALARY > 10000)
.ds

Here, AVG(E.SALARY BY E.DEPT WHERE E.SALARY>10000) is an AGGREGATE FUNCTION and takes
a value for each value of E.DEPT.  This value is the aggregate  AVG(E.SALARY
WHERE E.SALARY>10000 AND E.DEPT = value).  (For the toy, candy 
and admin departments this value is respectively 14,500, 12,000 and 30,000.)
The qualification expression for the
statement is then true for departments for which this aggregate function exceeds
the aggregate  AVG(E.SALARY WHERE E.SALARY>10000).  

In addition to the above QUEL commands 
INGRES also supports a variety of utility commands
These utility commands can be classified into 
seven
major categories.

a) invocation of INGRES

   INGRES data-base-name

This command executed from UNIX "logs in" a user to a given data base. 
(A data base is simply a named collection of
relations with a given data base administrator who has
powers not available to ordinary users.)
Thereafter, the user may issue all other commands
(except those executed directly from UNIX)
within the environment of the invoked data base.

b) creation and destruction of data bases

   CREATEDB data-base-name
   DESTROYDB data-base-name

These two commands are called from UNIX.  The invoker of CREATEDB 
must be authorized to create data bases (in a manner to be described 
presently) and he automatically becomes the data base administrator.
DESTROYDB successfully destroys a data base only if invoked by the data
base administrator.

c) creation and destruction of relations

.nf
   CREATE relname(domain-name IS format, domain-name IS format,...)
   DESTROY relname
.fi

These commands create and destroy relations within the current data base.
The invoker of the CREATE command becomes the "owner" of the relation 
created.  A user may only destroy a relation that he owns.
The current formats accepted by INGRES
are 1, 2 and 4 byte integers, 4 and 8
byte floating point numbers and fixed length ASCII character strings between
1 and 255 bytes.

d) bulk copy of data

.ss
   COPY relname(domain-name IS format, domain-name IS format,...) 
     direction  "filename"

   PRINT relname
.ds

The command COPY transfers an entire relation to or from a UNIX file whose
name is "filename".  Direction is either "TO" or "FROM".  The format for
each domain is a description of how it appears (or is to appear) in the 
UNIX file.  The relation relname must exist and have domain names identical 
to the ones appearing in the COPY command.  However, the formats need not agree and
COPY will automatically convert data types.  Also, support is provided 
for dummy and variable length fields in a UNIX file.

PRINT copies a relation onto the user's terminal  
formatting it
as a report.  In this sense, it is stylized version of COPY.

e) storage structure modification

   MODIFY relname TO storage-structure ON (key1, key2,...)
   INDEX ON relname IS indexname(key1, key2,...)

The MODIFY command changes the storage structure of a relation from one 
access method to another.  The five access methods currently supported are 
discussed in Section 2.  The indicated keys are domains in relname which are 
concatenated left to right to form a combined key which is used in the 
organization of tuples in all but one of the access methods.
Only the owner of a relation may modify its storage structure.

INDEX creates a secondary index for a relation .  It has domains of 
key1, key2,...,pointer.  The domain, pointer, is the address of a tuple 
in the indexed relation having the given values for key1, key2,....
An index named AGEINDEX for EMPLOYEE would be the
following binary relation

.ss
.nf
		AGE            POINTER

		25	address of Smith's tuple
		32	address of Jones' tuple
  AGEINDEX	36	address of Adams' tuple
		29	address of Johnson's tuple
		47	address of Baker's tuple
		58	address of Harding's tuple


.ds
.fi
The relation indexname is in turn treated and accessed just like any other 
relation except that it is automatically updated when the relation it indexes
is updated.  This is discussed further in Section 6.
Naturally, only the owner of a relation may create and destroy secondary
indexes for it.

f) consistency and integrity control

   INTEGRITY CONSTRAINT is qualification
   INTEGRITY CONSTRAINT LIST relname
   INTEGRITY CONSTRAINT OFF relname
   INTEGRITY CONSTRAINT OFF (integer, ... ,integer)
   RESTORE data-base-name

The first four commands support the insertion, listing, deletion 
and selective deletion of integrity constraints which are to be enforced for all
interactions with a relation.  The mechanism for handling this enforcement 
is dicussed in Section 4.  The last command restores a data base to a 
consistent state after a system crash.  It must be executed from UNIX and its 
operation is discussed in Section 6.
The RESTORE command is only available
to the data-base administrator.

g) miscellaneous

   HELP [relname|manual-section]
   SAVE relname UNTIL expiration-date
   RELKILLER  data-base-name

HELP provides information about the system or the data base invoked.  When 
called with an optional argument which is a command name, HELP will 
return the appropriate page from the INGRES reference manual [ZOOK75].
When called with a relation name as an argument, it returns all information 
about that relation.  With no argument at all it returns information about
all relations in the current data base.

SAVE is the mechanism by which a user can declare his intention to keep a 
relation until a specified time.  RELKILLER is a UNIX command which can be 
invoked by a data base administrator to delete all relations  
whose "expiration-dates" have passed.  This should be done when
space in a data base is exhausted.
(The data base administrator can also remove any
relations from his data base using the DESTROY command,
regardless of who their owners are.)

Two comments should be noted at this time.

a) The system currently accepts the language specified as QUEL1 in [HELD75a].
Extension is in progress to accept QUELn.

b) The system currently does not accept views or protection statements.  Although
the algorithms have been specified [STON74b,STON75], they have not yet been implemented.
For this reason, no syntax for these statements is given in this section;
however the subject is dicussed further in Section 4.

1.3  THE UNIX ENVIRONMENT

Two points concerning UNIX are worthy of mention in this section.

a) The UNIX file system

UNIX supports a tree structured file system similar to that of MULTICS.
Each file is either a directory (containing references to descendant 
files in the file system) or a data file.  Each data file can be viewed 
as an array 1 byte wide and 2**24 bytes long.  
(It is expected that this maximum length
will be increased by the UNIX implementors.)
Addressing in a file is similar
to referencing such an array.  Physically, each file is divided into 512 byte 
blocks (pages).  In response to a read request, UNIX moves one or more
pages from secondary memory to UNIX core buffers then returns to the user the 
the actual byte string desired.  If the same page is referenced again  
(by the same or another user) while
it is still in a core buffer, no disk I/O takes place.   

It is important to
note that UNIX pages data from
the file system into and out of system buffers
using a "least
recently used" replacement algorithm.  In this way the entire file system 
is managed as a large virtual store.

In part because the INGRES designers believe that a data base system 
should appear as a user job to UNIX and in part because they believe
that the operating system should deal with all space management issues 
for the mix of jobs being run, INGRES contains NO facilities to 
do its own memory management.

Each file in UNIX can be granted by its owner any combination of the 
following protection clauses:

.ss
 a) owner read
 b) owner write
 c) non owner read
 d) non owner write
 e) execute
 f) special execute
.ds

When INGRES is initially generated, a UNIX user named INGRES is 
created.  All data files managed by the INGRES system are 
owned by this "super-user" and have their protection status 
set to "owner read, owner write, no other access".  Consequently,
only the INGRES super-user can directly tamper with INGRES 
files.  (The protection system is currently being altered to 
optionally require the consent of the data base administrator 
before unrestricted access by the super-user is allowed.)

The INGRES object code is stored in files whose protection status is 
set to "special execute, no other access".  When a user invokes the 
INGRES system (by executing command a) above), UNIX creates the 
INGRES processes operating temporarily with a user-id of INGRES.  When 
a user exits from INGRES these processes are destroyed and the user is 
restored to operating with his own user-id.

Using this mechanism, the only way
a user may access an INGRES data base is to execute
INGRES object code.  This "safety latch" effectively isolates users from 
tampering directly with INGRES data.

b) The UNIX process structure

A process in UNIX is an address space (64K bytes or less on an 11/40,
128K bytes or less on 11/45's and 11/70's) which is associated with a user-id 
and is the unit of work scheduled by the UNIX scheduler.  Processes 
may "fork" subprocesses; consequently, a parent process can be the root of 
a process subtree.
Furthermore, a process can request that UNIX
execute a file in a descendant process.
Such processes may communicate with each other
via an inter-process communication facility called
"pipes".  A pipe
may be declared as a one direction
communication link which is written into
by one process and read by a second one.
UNIX maintains synchronization
of pipes so no messages are lost.
Each process has a "standard input device" and a "standard output device".
These are usually the user's terminal but may be redirected by
the user to be files, pipes to other
processes, or other devices.
.ph
Lastly UNIX provides a facility for processes executing
re-entrant code to share
procedure segments if possible.
INGRES takes advantage of this facility
so the core space overhead of multiple
concurrent users is only that
required by data segments.
.ph
We turn in the next section to the process structure in which INGRES runs.

.bp
.fo 'DESIGN OF INGRES (II)'-%-'12/5/75'
2  THE INGRES PROCESS STRUCTURE

INGRES can be invoked in two ways:  First, it can be directly invoked 
from UNIX by executing INGRES data-base-name; second it can be invoked by 
executing a program written using the EQUEL precompiler.  We discuss each 
in turn and then comment briefly on why two mechanisms exist.

2.1 INVOCATION FROM UNIX

Issuing INGRES as a UNIX command
causes the process structure shown in Figure 1 to 
be created.

.ne 15
.nf
________     ________     ________     ________     ________
|      |     |      |  A  |      |  B  |      |  C  |      |
| user |---->|      |---->|      |---->|      |---->|      |
| term-|     |      |     |      |     |      |     |      |
| inal |<----|      |<----|      |<----|      |<----|      |
|      |     |      |  F  |      |  E  |      |  D  |      |
________     ________     ________     ________     ________

             process      process      process      process
                1            2            3            4


                 INGRES Process Structure

                      Figure 1

.fi
Process 1 is an interactive terminal monitor which allows the user to 
formulate, print, edit and execute collections of INGRES commands.  It 
maintains a workspace with which the user interacts until he is 
satisfied with his interaction.
The contents of this workspace are passed
down pipe A as a string of ASCII characters
when execution is desired.
.ph
As noted above,
UNIX allows a user to alter the standard input and output devices for 
his processes when executing a command.  As a result the invoker of INGRES 
may direct the terminal monitor to take input from a user file  
(in which case he runs a "canned" collection of interactions)
and direct
output to another device (such as the line printer) or a file.

The current terminal monitor accepts the following commands.  Anything else 
is simply appended to the user's workspace.

.nf
.ss
	  #  :  Erase the previous character.  Successive uses of this
		instruction will erase back to, but not beyond, the
		beginning of the current line.

          @  :  Erase the current line.  Successive uses of  this  in-
		struction are ignored.

	\\r   :  Erase the entire interaction (reset the workspace).  The
		former contents of the workspace are irretrieveably lost.

	\\p   :  Print the current workspace.  Its contents are printed
		on the user's terminal.

	\\e   :  Enter the UNIX text editor and begin accepting editor
		commands.  The editor allows sophisticated editing of the
		user's workspace.  This command is executed by simply
		"forking" a subprocess and executing the UNIX editor in it.

	\\g   :  Process the current query (go).  The contents of the
		workspace are transmitted to process 2.

	\\q   :  Exit from INGRES.

.fi

.ds
Process 2 contains a lexical analyzer, a parser, query modification routines 
for integrity control (and in the future support of views and protection) 
and concurrency control.  When process 2 finishes, it passes a string of tokens 
to process 3 through pipe B.
Process 2 is discussed in Section 4.

Process 3 accepts this token string and contains execution routines for 
the commands
RETRIEVE, REPLACE, DELETE and APPEND.  Any update is  
turned into a RETRIEVE command to isolate
tuples to be changed.  Revised copies of modified tuples
are spooled into a special file.
This
file is then processed by a
"deferred update processor" in
process 4 which is discussed in Section 6.
.ph
Basically process 3 performs two functions for RETRIEVE commands.
a) A multivariable query is DECOMPOSED into a sequence of 
interactions involving only a single variable.
b) A one variable query is executed by a one variable query processor (OVQP).
OVQP in turn performs its function by making calls on the access methods.
These two functions are discussed in Section 5;
the access method are indicated in Section 3.

In process 4 resides all code to support utility commands (CREATE, DESTROY,
INDEX, etc.).  Process 3 simply passes to process 4 any commands which process 4 
will execute.
Process
4 is organized as a collection of overlays which accomplish the various 
functions.  The structure of this process will be discussed in Section 6.

Error messages are passed back through pipes D, E and F
to process 1 which returns
them to the user. If the command is a RETRIEVE with no result
relation specified, process 3 returns qualifying tuples 
in a stylized format directly to the
"standard output device" of process 1.
Unless redirected, this is the user's terminal.

We now turn to the operation of INGRES when invoked by code from the 
precompiler.

2.2  EQUEL

Although QUEL alone provides the flexibility for most data 
management requirements, there are many
applications which require a customized user
interface in place of the QUEL language.
For this as well as other reasons,
it is often useful to have the flexibility of a general purpose
programming language in addition to the
data base facilities of QUEL.
To this end, a new language, EQUEL (Embedded QUEL), has
been implemented which consists of QUEL embedded in the general purpose
programming language "C".

In this section we describe the EQUEL language and indicate how it
operates in the INGRES environment.

In the design of EQUEL, the following goals were set:
.in +5
.ti -3
1)&The new language must have the full capabilities of both
"C" and QUEL.
.ti -3
2)&The C program should have the capability for processing
each tuple individually which satisfies the qualification
in a QUEL RETRIEVE statement.
(this is the "piped" return facility described in
Data Language/ALPHA [CODD71]).
.ti -3
3)&The implementation should make as much use as possible
of the existing C and QUEL language processors. 
(The implementation cost of EQUEL should be small).
.in -5

With these goals in mind, EQUEL was defined as follows:
.in +5
.ti -3
1)&Any C language statement is a valid EQUEL statement.
.ti -3
2)&Any QUEL statement (or INGRES utility command)
is a valid EQUEL statement as long as it is
prefixed by two number signs ("##").
.ti -3
3)&C program variables may be used in QUEL statements in place
of relation names, domain names, target list elements,
or domain values.
The declaration statements of C variables used in this manner
must also be prefixed by double number signs.
.ti -3
4)&RETRIEVE statements without a result relation have the form
	RETRIEVE (Target-list) 
		 [WHERE Qualification] C-Block
.br
which results in the C-Block
being executed once for each qualifying tuple.
.in -5

Two short examples illustrate EQUEL syntax.

Example 2.1  The following section of code implements a small
front end to INGRES which performs only one query.
It reads in the name of an employee and prints out the
employee's salary in a suitable format.
It continues to do this as long as there are more names
to be read in.
The functions READ and PRINT are assumed to have the obvious meaning.

.nf
.ss
.in +4
main()
{
## char NAME[20];
## int SAL;
while (READ(NAME))
	{
##	RANGE OF X IS EMP
##	RETRIEVE (SAL = X.SALARY) 
##	WHERE X.NAME = NAME
		{
		PRINT("The salary of ",NAME," is ",SAL);
		}
	}
}

.fi
.ds
In this example the C-variable NAME is used in the qualification of
the QUEL statement and for each qualifying tuple,
the C-variable SAL is set to the appropriate value and then
the Print statement is executed.
(note: in C "{" and "}" are equivalent to BEGIN and END in ALGOL).

.in -4


Example 2.2  Read in a relation name and two domain names.
Then for each of a collection of values which the second
domain is to assume,
do some processing on all values
which the first domain assumes.
(We assume the functions READ and PROCESS exist and have the
obvious meanings.)
A more elaborate version of this program could serve as a simple 
report generator.

.nf
.ss
.in +4
## int VALUE;
## char RELNAME[13], DOMNAME[13], DOMVAL[80];
## char DOMNAME_2[13];
READ(RELNAME);
READ(DOMNAME);
READ(DOMNAME_2);
## RANGE OF X IS RELNAME
while (READ(DOMVAL))
        {
##      RETRIEVE (VALUE = X.DOMNAME)
##          WHERE X.DOMNAME_2 = DOMVAL
                {
                PROCESS(VALUE);
                }
        }
.fi
.in -4
.ds

Any RANGE declaration (in this case the one for X) is assumed by 
INGRES to hold until redefined.
Hence, only one RANGE statement is required regardless of the number 
of times the RETRIEVE statement is executed.

In order to implement EQUEL, a translator (pre-compiler)
was written which converts an EQUEL program into a valid C-program
with QUEL statements converted to appropriate C-code and calls to
INGRES.
The resulting C-program is then compiled by the normal
C-compiler producing an executable module.
Moreover, when an EQUEL program is run, the executable module
produced by the C-compiler is used as the 
front end process in place of the interactive terminal monitor as noted 
in Figure 2.
.ne 15
.nf

             ________     ________     ________     ________
             |      |  A  |      |  B  |      |  C  |      |
             |      |---->|      |---->|      |---->|      |
             |      |     |      |     |      |     |      |
             |      |<----|      |<----|      |<----|      |
             |      |  F  |      |  E  |      |  D  |      |
             ________     ________     ________     ________

                C         process      process      process
             program         2            3            4


                         The Forked Process Structure

                                Figure 2

.fi
During execution of the front-end program,
data base requests (QUEL statements in the EQUEL program)
are passed through pipe A and processed by INGRES.
If tuples must be returned for tuple at a time processing,
then they are returned through a special data pipe set up between process 3 and the C program.
A condition code is also returned
through pipe F to indicate success or the type of error encountered.

Consequently, the EQUEL translator must perform the following five 
functions:

.in +5
1) insert system calls to "spawn" at run time the process structure 
shown in Figure 2.

2) note C-variable declarations prefaced by ## as legal for inclusion 
in INGRES commands.

3) process other lines prefaced by ##.  These are parsed to isolate
C-variables.  In adddition, C statements are inserted to write the 
line down pipe A in ASCII format, modified so that 
values are substituted for any C-variables.
The rationale for not completely parsing a QUEL statement in EQUEL 
is given in [ALLM76].

4) insert C statements to read pipe F for completion information 
and call the procedure IIerror.
The user may define IIerror himself or have EQUEL include a standard 
version which prints the error message (for abnormal terminations) 
and continues.

5) If data is to be returned through the data pipe (by a RETRIEVE with no result
relation specified), EQUEL must also:

.in +5
a) insert C statements to read the data pipe for a tuple formatted as type/value
pairs.

b) insert C statements to substitute values into C-variables declared in the
target list.
If necessary, values are converted to the types of the declared C-variables.

c) insert C statements to pass control to the C-block following the RETRIEVE.

d) insert C statements following 
the block to return to step a) if there are more tuples.
.in -10


2.3 COMMENTS ON THE PROCESS STRUCTURE

The process structure shown in Figures 1 and 2 is the fourth different process 
structure implemented.  The following considerations suggested this final choice:

a) Simple control flow.  Previous process structures had a more complex 
interconnection of processes which made debugging harder.   

b) Commands are passed to the right only.  Process 3 must issue commands 
to various overlays in process 4 to execute interactions as discussed in 
Section 5.  Hence, process 3 must be to the left of process 4.

c) The utility commands are expected to be called relatively infrequently 
compared to the activity in process 2 and 3.  Hence, it appears appropriate 
to overlay little used code in a single process.
The alternative is to create additional processes (and pipes)
which are quiescent most of the time.  This would
require added space in UNIX core tables for no particular advantage.

d) The first 3 processes are used frequently. 
Overlaying code in these processes was
tried in a previous version and slowed the
system considerably.

e) To run on an 11/40, the 64K address space limitation must be adhered to.  Processes
2 and 3 are nearly their maximum size and hence cannot be combined. 
(For 11/45 and 11/70 versions we may experiment with such a combination.) 

f) The C program which replaces the terminal monitor as a front 
end must run with a user-id different from that of INGRES for protection reasons. 
(Otherwise it could tamper directly with data
managed by INGRES.)
Hence, either it must be overlayed into a process or run in its 
own process.  For efficiency and convenience, the latter was chosen.

g) The interactive terminal monitor could have been written (albeit 
clumsily) in EQUEL.  Such a strategy would have avoided the 
existence of two process structures which differ only by the
treatment of the data pipe.  This was not done because response time 
would have degraded and because EQUEL does type 
conversion to predefined types.  This feature would unnecessarily 
complicate the terminal monitor.

h) The processes are all synchronized (i.e. each waits for an
error return from the next process to the right before continuing to accept
input from the process to the left.
This is done because it simplifies the flow of
control.  Moreover in many instances the
various processes MUST be synchronized.
Future versions of INGRES may attempt to exploit parallelism 
where possible.

.fo 'DESIGN OF INGRES (III)'-%-'12/5/75'
.bp
3  DATA STRUCTURES AND ACCESS METHODS
.ph
We begin this section with a discussion of the files
that INGRES manipulates and their contents.
Then we sketch the language used to access all
non directory files.
Finally, the five possible file formats are indicated.
.se
3.1 THE INGRES FILE STRUCTURE
.ph
Figure 3 indicates the subtree of the UNIX
file system that INGRES manipulates.

.ss


















       
.ce 3
The INGRES Subtree

Figure 3

.ds

The root of this subtree
is a directory made for the UNIX user "INGRES".
It has six descendant directories.  The AUX
directory contains descendant files containing tables which
control the spawning of processes shown in
Figures 1 and 2, and an authorization list of users who are allowed to
create data bases.  Only the INGRES "super-user"
may modify these files (by using the UNIX editor).
BIN and SOURCE are directories indicating descendant
files of respectively object and source code.
TMP contains temporary files containing
the workspaces used by the interactive
terminal monitor.
DOC is the root of a subtree with system documentation and the reference manual.
Lastly there is a directory entry in DATADIR for each data base that
exists in INGRES.
These directories contain the data base files 
in a given data base as descendants.
.ph
These data base files are of four types:
.ph
a)  an administration file.  This contains the user-id
of the data base administrator (DBA) and 
initialization information.
.ph
b)  System relations.  These relations have
predefined names 
and are created for every data base.
They are owned by the DBA and 
constitute the system catalogs.
They may be queried by a knowledgeable user
issuing RETRIEVE statements,
however, they may be updated only by the INGRES utility commands
(or directly by the INGRES "super-user" in an emergency).
(When protection statements are implemented the DBA
will be able to selectively restrict RETRIEVE access
to these relations if he wishes.)
The form and content of some of these relations will be presently discussed.
.ph
c)  DBA relations.  These are relations owned by the DBA and are
shared in that any user may
access them.
When protection
is implemented the DBA can "authorize" other users by inserting protection
predicates (which will be in one of the system relations) and
"deauthorize" them by removing such predicates.
.ph
d)  Other relations.  These are relations
created by other users (by RETRIEVE into W or CREATE)
and are NOT SHARED.
.ph
Three comments should be made at this time.
.ph
a)  The DBA has the following power not available
to ordinary users:
.bb
1) the ability to create shared relations and to specify access control
for them
.ph
2) the ability to run RELKILLER
.ph
3) the ability to destroy any relations in his data base (except the
system catalogs)
.be
This system allows "one level sharing" in that only the DBA has
the powers in a) and he cannot delegate any of these
powers to others (as in the file systems of most
time-sharing systems).  This strategy was implemented for
three reasons:
.bb
1) The need for added generality was not perceived.
Moreover, added generality would have created
tedious problems (such as making revocation 
of access privileges
non trivial).
.ph
2) It seems appropriate to entrust to the DBA the duty (and power) to resolve
the policy decision which must be made when
space is exhausted and some relations must be destroyed (or archived).  
This policy decision becomes much harder (or impossible)
if a data base is not in the control of one user.
.ph
3) Someone must be entrusted with the policy
decision concerning which relations to physically store and which to
define as "views".  This "data base design" problem is
best centralized in a single DBA.
.be
b) Except for the single administration file in each data base 
every file
is treated as a relation.
Storing system catalogs as relations
has the following advantages:
.bb
1) Code is economized by
sharing routines for accessing both catalog and data relations.
.ph
2) Since several storage structures are supported for 
accessing
data relations quickly and flexibly under various interaction mixes, these same
storage choices may be utilized to enhance access to catalog information.
.ph
3) The ability to execute QUEL statements to examine (and patch)
system relations where necessary has greatly
aided system debugging.
.be
c)  Each relation is stored in a separate file, i.e., no attempt
is made to "cluster" tuples from different relations 
which may be accessed together
on the same
(or a nearby) page. 
This decision is based on the following reasoning.
.bb
1) The access methods would be more complicated if clustering were
supported.
.ph
2) UNIX has a small (512 byte) page size.
Hence it is expected that the number of tuples which can be grouped
on the same page is small.
Moreover, logically adjacent pages in a UNIX file are NOT
NECESSARILY physically adjacent.
Hence clustering tuples on "nearby" pages has no meaning in
UNIX; the next logical page in a file
may be further away (in terms of disk arm motion) than a page in a
different file.  In keeping with the design decision of NOT
modifying UNIX, these considerations were incorporated
in the design decision not to support clustering.
.ph
3) Clustering of tuples only makes sense if associated
tuples can be linked together using "sets" [CODA71] or
"links" [TSIC75].  Incorporating these access paths into the 
decomposition scheme would have greatly increased its complexity.
.be
.se
3.2  SYSTEM CATALOGS
.ph
We turn now to a discussion of the system catalogs. 
We discuss two relations in detail and
indicate briefly the contents of the others.
.ph
The RELATION relation contains one tuple
for every relation in the data base (including all the system
relations.)  The domains
of this relation are:
.in +24
.na
.ti 8
relid		the name of the relation
.ti 8
owner		the UNIX user-id of the relation owner; 
when appended to relid it produces a unique file name for storing
the relation.
.ti 8
spec		indicates one of 5 possible storage
schemes or else a special code indicating a virtual
relation (or "view").
.ti 8
indexd		flag set if secondary index exists for this
relation.  (This flag and the following two are
present to improve performance by avoiding catalog
lookup's when possible during query modification
and one variable query processing.)
.ti 8
protect		flag set if this relation has protection predicates.
.ti 8
integ		flag set if there are integrity constraints.
.ti 8
save		scheduled life time of relation.
.ti 8
tuples		number of tuples in relation.
.ti 8
atts		number of domains in relation.
.ti 8
width		width (in bytes) of a tuple.
.ti 8
prim		number of primary file pages for this relation.
.in -24
.ad
.ph
The ATTRIBUTE catalog contains information relating to
individual domains of relations.
Tuples of the ATTRIBUTE catalog contain the following items
for each domain of every relation in the data base:

.in +24
.na
.ti 8
relid		name of relation in which attribute appears
.ti 8
owner		relation owner
.ti 8
domain-name	domain name
.ti 8
domainno	domain number (position) in relation.  In processing
interactions INGRES uses this number to reference this domain.
.ti 8
offset		offset in bytes from beginning of tuple to beginning of domain.
.ti 8
type		data type of domain (integer, floating point or character string).
.ti 8
length		length (in bytes) of domain; 
.ti 8
keyno		if this domain is part of a key, then "keyno"
indicates the ordering of this domain within the key.
.in -24
.ad
.ph
These two catalogs together provide information about the structure and 
content of each relation in the data base.  
No doubt items will continue to be added or deleted as the system undergoes
further development. 
The first planned extensions are the minimum and maximum values 
assumed by the domain.
These will be used by a more sophisticated decomposition scheme being 
developed, which is discussed
briefly in the next section and in detail in [WONG76].
The representation of the catalogs as relations
has allowed this restructuring to occur very easily.
.ph
Several other system relations exist which provide auxiliary
information about relations.
The INDEX catalog contains a tuple for every
secondary index in the data base.
Since secondary indices are themselves relations
they are independently cataloged in the RELATION and ATTRIBUTE
relations.  However, the INDEX catalog provides the association
between a primary relation and the secondary indices for it
including which domains of the primary relation are in the index.
.ph
The PROTECTION and INTEGRITY catalogs contain respectively
the protection and integrity predicates for each relation in the 
data base.
These predicates are stored in a partially processed 
form as character strings.
(This mechanism exists for INTEGRITY and will be implemented
in the same way for PROTECTION.)
The VIEW catalog will contain, for each virtual relation, a partially
processed QUEL-like description which can be used to 
construct the view from its component physical relations.
The use of these last three catalogs will be described in 
Section 4.
The existence of any of this auxiliary information for
a given relation is signalled by the appropriate flag(s) in
the RELATION catalog.
.ph
Yet another set of system relations are those used by the
graphics sub-system to catalog and process maps, which (like
everything else) are stored as relations in the data base.
This topic has been discussed separately in [GO75].
.se
3.3 ACCESS METHODS INTERFACE (AMI).
.ph
We will now discuss in more detail the AMI which handles
all actual accessing of data from relations.
The AMI language is implemented as a set of functions whose calling 
conventions are indicated below. 

.ph
Each access method must do two things to support the
following calls.  First it must provide SOME
linear ordering of the tuples in a relation so
that the concept of "next tuple" is well defined.
Second it must assign to each tuple a tuple-id (TID) which
uniquely identifies a tuple.
.ph
The nine implemented calls are as follows:
.ph
a)  openr(descriptor, mode, relation_name)
.ph
Before a relation may be accessed it must be "opened".
This function opens the UNIX file for the relation and fills in
a "descriptor"
with information about the relation from the RELATION and ATTRIBUTE
catalogs.
The descriptor, which must be declared in the calling program, is used
in subsequent calls on AMI routines as an input parameter 
to indicate what relation is involved.
Consequently, the AMI data accessing routines need not themselves check the
system catalogs for the description of a relation.
"Mode" specifies whether the relation is being opened for update or
for retrieval only.
.ph
b)  get(descriptor, tid, limit_tid, tuple, next_flag)
.ph
This function retrieves into 'tuple' a single tuple from the relation indicated by 'descriptor'.
\'tid' and 'limit_tid' are tuple-identifiers.
There are two modes of retrieval, "scan" and "direct".
In "scan" mode "get" is intended to be called successively to 
retrieve all tuples within a range of tuple-id's. 
An initial value of 'tid' sets the low end of the range desired
and 'limit_tid' sets the high end.
Each time "get" is called with 'next_flag' = TRUE, the 
tuple following
\'tid' is retrieved and its tuple-id placed into 'tid' in readiness
for the next call.
Reaching 'limit_tid' is indicated by a special return code.
The initial setting of 'tid' and 'limit_tid' is done
by the "find" function.
In "direct" mode ('next_flag' = FALSE) the function retrieves
the tuple with tuple-id = 'tid'.
.ph
c)  find(descriptor, key, tid, match_mode)
.ph
"Find" places in 'tid' the tuple-id at the low or high end
of the range of tuples which match the key value supplied.
The matching condition to be applied depends on 'match-mode'.
.ph
If the relation does not have a keyed storage structure
or if the key supplied does not correspond to the correct key domains,
the 'tid' returned will be as if no key were supplied.
The objective of "find" is to restrict the scan of a relation
by eliminating from consideration those tuples known from
their placement in the relation not to satisfy the
matching condition with the key.
Calls to "find" occur in pairs, one to set the low end of a scan,
the other for the high end,
and the two tuple-id's obtained are used in subsequent calls on "get".
.ph
Two functions are available for determining the access characteristics
of the storage structure
of a primary data relation or secondary index,
respectively.
.ph
d)  paramd(descriptor, access_characteristics_structure)
.br
e)  parami(descriptor, access_characteristics_structure)
.ph
These functions fill in the 'access_characteristics_structure' with 
information regarding the type of key which may be constructed
to optimize access to the given relation.
This includes whether exact key values or ranges of key values can be used,
and whether a partially specified key may be used.
This will determine the 'match-mode' used in a subsequent call to "find".
The ordering of domains in the key is also indicated.
These functions relieve optimization routines executed
during the processing of an interaction
of the need to know directly about specific storage structures.
.ph
Other AMI functions provide a facility for updating relations.
.ph
f)  insert(descriptor, tuple)
.ph
The tuple is added to the relation in  its "proper" place
according to its key value and the storage mode of the relation.
.ph
g)  replace(descriptor, tid, new_tuple)
.br
h)  delete(descriptor, tid)
.ph
The tuple indicated by 'tid' is either replaced by new values
or deleted from the relation altogether.
The tuple-id of the affected tuple will have been obtained by a previous
"get".
.ph
Finally, when all access to a relation is complete it must be closed:
.ph
i)  closer(descriptor)
.ph
This closes the relation's UNIX file and rewrites the information
in the descriptor back into the system catalogs if there has been
any change.
.se
3.4 STORAGE STRUCTURES AVAILABLE.
.ph
We will now describe the five storage structures currently available in INGRES.
Four of the schemes are keyed, i.e., the storage location of a tuple within the
file is a function of the value of the tuple's key domains.
These schemes allow rapid access to specific portions of a relation
when key values are supplied. The remaining non-keyed scheme stores tuples
in the file independently of their values
and provides a low-overhead storage structure, especially attractive when
the entire relation must be accessed anyway.
.ph
The non-keyed storage structure in INGRES is a randomly ordered sequential
file.
Fixed-length tuples are
simply placed sequentially in the file in the order supplied.
New tuples added to the relation are merely appended to the end
of the file. 
The unique tuple-identifier for each tuple is its byte-offset within
the file.
This mode is intended mainly for 
.ph
a) very small relations, for which the overhead of other schemes
is unwarranted
.ph
b) transitional storage of data being moved into or out of the system by COPY;
.ph
c) certain temporary relations created as intermediate results during query
processing.
.be
In the remaining schemes, the key-value of a tuple determines
the page of the file on which the tuple will
be placed. 
The schemes share a common "page-structure" for managing
tuples on file pages as shown in Figure 4.
.ne 15















.ce 2
Page Layout for Keyed Storage Structures
Figure 4
.ph
A tuple must fit entirely on a single page.
Its unique identifier (TID) consists of a page number
(the ordering of its page in the UNIX file)
plus a "line
number" indicating its position on the page.
A "line table", which grows upwards from the bottom of the page,
contains as an entry for each tuple, a pointer to the beginning of
the tuple.
In this way a page can be reorganized without affecting TID's.
.ph
Initially the file will contain all its tuples on a number of 
"primary" pages.
If the relation grows and these pages fill, "overflow"
pages are allocated and chained by pointers to the primary pages
with which they are associated.
Within a chained group of pages no
special ordering of tuples is maintained.
Thus in a keyed access which locates a particular primary page,
tuples matching the key may be on any page in the chain.
.ph
As discussed in [HELD75b] two modes of key-to-address transformation
are used -- randomizing and order preserving.
In a "hash" file tuples are distributed randomly throughout
the primary pages of the file according to a hashing function
on a key.
This mode is well suited for situations in which access
is to be conditioned on a specific
key value.
.ph
As an order-preserving mode, a scheme similar to IBM's ISAM [IBM66]
is used.
The relation is sorted to produce the ordering on a particular key.
A multi-level directory is created which records the high key on each
primary page.
The directory, which is static, resides on several pages within the file itself,
following the primary pages.
A primary page and its overflow pages are not maintained in sort order.  This
decision is discussed in the section on concurrency.
The "ISAM-like" mode is useful in cases where the key value is likely
to be specified as falling within a range of values, since
a near ordering of the keys is preserved.
The index compression scheme discussed in [HELD75b] is
currently under implementation.
.ph
In the above mentioned keyed modes, fixed length tuples are stored.
In addition, both schemes can be used in conjunction with data compression
techniques [GOTT75] in cases
where increased storage utilization outweighs the added cost of
encoding and decoding data during access. 
These modes are known as "compressed hash" and "compressed ISAM".

The current compression scheme suppresses blanks and portions of a 
tuple which match the preceding tuple.  This compression is applied 
to each page independently.  Other schemes are being experimented with.
.ph

3.5  ADDITION OF NEW ACCESS METHODS

.ph
One of the goals of the AMI design was to insulate
higher level software from the actual functioning
of the access methods and thereby to make it
easy to add different ones.
.ph
In order to add a new access method one need
only extend the AMI routines to handle the new case.
If the new method uses the same page layout and TID scheme,
only find, parami, and paramd need to be extended.
Otherwise new procedures to perform these functions must be
supplied for use by get, insert, replace and delete.
.bp
.fo 'DESIGN OF INGRES (IV)'-%-'12/5/75'
4  THE STRUCTURE OF PROCESS 2

Process 2 contains code to perform four main functions
.br
a)  a lexical analyzer
.br
b)  a parser (written in YACC [JOHN74])
.br
c)  query modification routines to support
protection, views and integrity control
.br
d)  concurrency control
.in 0

These are discussed in turn

4.1  LEXICAL ANALYSIS AND PARSING
.ph
The lexical analysis and parsing phases of
INGRES have been organized around the
YACC translator writing system
available in UNIX [JOHN74].  YACC takes
as input a description of a grammar consisting
of BNF-like parsing rules (productions) and
precedence rules,
plus action statements associated with
each production.
It produces a set of tables to be
interpreted by a parse table interpreter which is combined
with locally-supplied lexical analysis
and parsing action routines to produce a complete translator.
.ph
The interpreter uses a bottom-up
LR(1) parsing approach.
The lexical analyzer is called to obtain successive symbols
from the input stream as the interpreter attempts to
match the input with productions in the grammar.
When a production is matched YACC performs a reduction and
executes the action statement associated with
the production.  YACC has a mechanism for recovering
from errors to continue parsing input in its
entirety.
.ph
While the YACC parse table interpreter checks
the syntactic correctness of the input
commands, the action statements check for sementic
consistency and correctness and prepare the commands for
further processing.  The system
catalogs are used to check that relation and
domain names, formats, and so on, are
specified appropriately.  
.ph
For utility commands a command indicator
and the parameters for the
command are sent directly to process 3
for transmission to process 4.  Section 6 discusses these
commands and their implementation.
.ph
For QUEL commands, the input is translated to a tree-structured
internal form which will be used in the
remaining analysis and processing.  
Moreover, the qualification part
is converted to conjunctive normal form.
The parse tree is now ready to undergo
what has been termed "query-modification," to be described in
Section 4.2 and 4.3.
.br

4.2  INTEGRITY
.ph
Query modification includes adding integrity and
protection predicates to the original query
and changing references to virtual relations into references
to the appropriate physical relations.
At the present time only a simple integrity
scheme has been implemented.
.ph
In [STON75] algorithms of
several levels of complexity are presented for
performing integrity control on updates.
In the present system only the simplest case,
involving single-variable, aggregate-free
integrity assertions, has been implemented and is
described in detail in [SCHO75].
.ph
Briefly, integrity assertions are entered
in the form of QUEL qualification
clauses to be applied to interactions updating
the relation over which the variable in the
assertion ranges.  A parse
tree is created for the qualification and a representation of this
tree stored in the INTEGRITY catalog together with
an indication of the relation and specific domains
involved.  At query
modification time, updates are checked
for any possible integrity assertions
on the affected domains.  Relevant assertions are
retrieved, re-built into tree
form and grafted onto the update tree
so as to AND the assertions with the existing
qualification of the interaction.
.ph
4.3  PROTECTION AND VIEWS
.ph
Algorithms for the support of views are also given
in [STON75].  Basically a view is any relation
which could be created from existing relations by
the use of a RETRIEVE command.  Such view definitions
will be treated in a manner
somewhat analogous to that used for integrity
control.  They will be allowed in INGRES
to support EQUEL programs written for obsolete
versions of the data base and for user
convenience.
.ph
Protection will be handled according to the
algorithm described in [STON74b].  Like integrity control
this algorithm involves adding
qualifications to the user's interaction.
In the remainder of this section we distinguish this protection
scheme from the one in [CHAM75] and indicate the
rationale behind its use.
.ph
Consider the following two views:

.in 10
.ss
RANGE OF E IS EMPLOYEE
.br
DEFINE RESTRICTION-1 (E.NAME, E. SALARY, E.AGE)
.br
WHERE E.DEPT = "toy"

DEFINE RESTRICTION-2 (E.NAME, E.DEPT, E.SALARY)
.br
WHERE E.AGE < 50
.ds

.in 0
and the following two access control statements:

.in 10
.ss
RANGE OF E IS EMPLOYEE
.br
PROTECT (E.NAME, E.SALARY, E.AGE) 
.br
WHERE E.DEPT = "toy"

PROTECT (E.NAME, E.SALARY, E.DEPT) 
.br
WHERE E.AGE < 50
.ds

.in 0
.ph
Acess control could be based on
views as suggested in [CHAM75]
and a given user could be authorized to use
views RESTRICTION-1 and RESTRICTION-2. 
To find
the salary of Harding he could interrogate RESTRICTION-1 as
follows:

.in 10
.ss
RANGE OF R IS RESTRICTION-1
.br
RETRIEVE (R.SALARY) WHERE
.br
R.NAME = "Harding"
.ds
.in 0

.ph
Failing to find Harding in RESTRICTION-1 he would
have to then interrogate RESTRICTION-2.  After two queries
be would be returned the appropriate salary if
Harding was under 50 or in the toy department.
.ph
Under the INGRES scheme the user can issue
.in 10

.ss
RANGE OF E IS EMPLOYEE
.br
RETRIEVE (E.SALARY) WHERE
.br
E.NAME = "Harding"
.ds
.in 0
.ph
which will be modified by the access control
algorithm to
.in 10

.ss
RANGE OF E IS EMPLOYEE
.br
RETRIEVE (E.SALARY) WHERE
.br
E.NAME = "Brown"
    AND
.br
(E.AGE < 50 OR E.DEPT = "toy")
.ds
.in 0
.ph
In this way the user need not manually sequence through
his views to obtain desired data but automatically
obtains such data if permitted.  Note
clearly that the portion of EMPLOYEE to which the
user has access (the union of RESTRICTION-1 and RESTRICTION-2) is
not a relation and hence
cannot be defined as a single view.

To summarize, access control restrictions are handled automatically by the
INGRES algorithms but must be dealt with by a
user sequencing through his views in a "view
oriented" access control scheme.

4.4  CONCURRENCY CONTROL

In any multiuser system provisions must be included
to ensure that multiple concurrent updates are
executed in a manner such that some level
of data integrity can be guaranteed.  The
following two (somewhat facetious) updates illustrate the problem.

.nf
.ss

		RANGE OF E is EMPLOYEE
	U1	REPLACE E(DEPT = "toy") WHERE
        		E.DEPT = "candy"

		RANGE OF F is EMPLOYEE
	U2	REPLACE F(DEPT = "candy") WHERE
	                F.DEPT = "toy"

.ds
.fi
	If U1 and U2 are executed concurrently with
no controls, some employees may end up in
each department and the particular result
may not be repeatable if the data base is
backed up and the interactions reexecuted.

	The control which must be provided is to guarantee
that some data base operation is "atomic" (i.e. occurs
in such a fashion that it appears instantaneous and before
or after any other data base operation).
This atomic unit will be called a transaction.
.ph
In INGRES there are three basic choices available for
defining a transaction.

.br
a)  something smaller than one INGRES command
.br
b)  one INGRES command
.br
c)  a collection of INGRES commands.
.in 0
.br

If a) is chosen INGRES could not guarantee that two concurrently executing update
commands gave the same result as if they were executed sequentially (in either order)
in one collection of INGRES processes.
In fact the outcome could fail to be repeatable,
as noted in the example above.
This situation is clearly undesirable.

Option c) is in the opinion of the INGRES designers
impossible to support.
The following transaction could be declared in an EQUEL program.

.in 5
.br
.ss
BEGIN TRANSACTION
.in 10
FIRST QUEL UPDATE
.br
SYSTEM CALLS TO CREATE AND DESTROY FILES
.br
SYSTEM CALLS TO FORK A SECOND COLLECTION OF INGRES PROCESSES TO WHICH
COMMANDS ARE PASSED
.br
SYSTEM CALLS TO READ FROM A TERMINAL
.br
SYSTEM CALLS TO READ FROM A TAPE
.br
SECOND QUEL UPDATE (whose form depends on previous two
system calls)
.br
.in 5
END TRANSACTION
.ds

.in 0
Suppose T1 is the above transaction and runs concurrently with
a transaction T2 involving commands of the same
form.  The second update of each transaction may well "conflict" with the first
update of the other.
Note that there is no way to tell apriori that T1 and T2 conflict
because the form of the second update is
not known in advance.  Hence a deadlock situation
can arise which can
only be resolved by aborting one
transaction (an undesirable policy in the eyes of the INGRES designers)
or attempting to back out one transaction.
The overhead of backing out through the intermediate system
calls appears prohibitive (if it is possible at all).
Restricting a transaction to have no system calls (and hence
no I/0) cripples the power of a transaction in order to make deadlock resolution
possible and was judged undesirable.
Thus option b) was chosen.

The implementation of b) can be achieved by physical
locks on data items, pages, tuples, domains, relations, etc.
[GRAY75] or by predicate locks [STON74c].
The current implementation is by relatively crude physical
locks (on domains of a relation) and avoids deadlock by not
allowing an interaction to proceed to process 3 until it can lock all
required resources.
Because of a problem with the current design of certain access
method calls, all domains
of a relation must currently be locked (i.e. a whole relation is locked)
to perform an update.  This situation will soon be rectified.

The choice of avoiding deadlock rather than
detecting and resolving it is made primarily for implementation
simplicity.  The choice of a crude locking unit
reflects a minicomputer environment where core storage for
a large lock lable is not available.  In the future we
plan to experimentally implement a crude and (thereby low CPU overhead)
version of a predicate locking scheme previously described in [STON74c].
Such an approach may provide considerable concurrency at an
acceptable overhead in lock table space and CPU time,
although such a statement is highly speculative.

Once the concurrency processor has
assembled locks on all domains needed by an interaction, it may
proceed to process 3 for unemcumbered execution.

To conclude this section we briefly indicate the reasoning behind
not sorting a page and its overflow pages in the "ISAM-like" access method.  This 
topic is also discussed in [HELD75c].

Basically, maintenance of the sort order of these pages may require the access
method to lock more than one page when it inserts a tuple.
Clearly deadlock might be possible given concurrent updates and 
locks for physical pages would be required 
(at least once
a more sophisticated predicate locking scheme is tried such as [STON74c]).
To avoid both problems these pages remain unsorted and
the access method need only be able to read-modify-write a single
page as an atomic operation.
Although such an atomic operation is not currently in UNIX
(and not needed by the current primitive scheme) it is a minor
addition.


.bp
.fo 'DESIGN OF INGRES (V)'-%-'12/12/75'
5  PROCESS 3

.ph
As noted in Section 2 this process performs the following two
functions which will be discussed in turn:
.ph
a)  the DECOMPOSITION of queries involving more than one variable
into sequences of one-variable queries.  Partial results are
accumulated until the entire query is evaluated.  This program is called DECOMP.
It also turns any updates into the appropriate queries to isolate 
qualifying tuples and spools new values into a special file 
for deferred update.
.ph
b)  the processing of a single variable queries.
The program is called
the one variable query processor (OVQP).

.ph
5.1  DECOMP

Because INGRES allows interactions which are defined on the
cross product of perhaps several relations, efficient execution of
this step is of crucial importance in order to search as small a
portion of the appropriate cross product space as
possible.
DECOMP uses three techniques in processing
interactions.  We describe each technique then
give the actual algorithm implemented.  Finally, we
indicate the role of a more sophisticated decomposition scheme under
design.
.ph
a)  Tuple substitution

The basic technique used by DECOMP to reduce a query
to fewer variables is tuple substitution.
One variable (out of possibly many) in the
query is selected for substitution.  The AMI
language is used to scan the relation
associated with the variable one tuple at a time.
For each tuple, the values of domains in that relation
are substituted into the query.
In the resulting modified query, all
previous references to the substituted variable have now
been replaced by values (constants), and the query has
thus been reduced to one less variable.  Precomposition
is repeated (recursively) on the modified query until
only one variable remains, at which point the OVQP is called to continue processing.
.ph
b)  One-Variable Detachment

If the qualification Q of the query is of the form
.br
.ce
Q1(V1)  AND  Q2(V1,...,Vn)
.br
for some
tuple variable V1, the following two steps can be
executed:

1)  Issue the query
.in 5
.ss

RETRIEVE INTO W (TL[V1])
.br
WHERE Q1[V1]
.ds
.in 0
.ph
Here TL[V1] are those domains required in the remainder
of the query.  Note that this is a one variable query and may
be passed directly to OVQP.

2)  Replace R1, the relation over which V1 ranges,
by W in the range declaration and delete
Q1[V1] from Q.

.ph
The query formed in 1) is called a "one-variable,
detachable sub-query" (OVDSQ) and the technique
for forming and executing it "one-variable detachment" (OVD).
This step has the effect of reducing the size
of the relation over which V1 ranges
by restriction and projection.
Hence, it may reduce the complexity of the
processing to follow.
.ph
Moreover, the opportunity exists in the process
of creating new relations through OVD, to choose storage structures
(and particularly keys) which will prove
helpful in further processing.
.ph

c)  Reformatting

When a tuple variable is selected for substitution, a large
number of queries each with one less variable will
be executed.  If b) is a possible operation after
the substitution for some 
remaining variable, V1, then the relation over which
V1 ranges, R1, can be reformatted to have domains
used in Q1(V1) as a key.  This will expedite
b) each time it is executed during tuple substitution.

We can now state the complete decomposition algorithm.
.ph
a)  If number of variables
in query is 0 or 1 call OVQP and  stop; else go on.

b)  Find all variables,
{V1,...Vn},
for which the query contains a 
one-variable clause.  Perform
OVD to create new ranges for each of these
variables.
The new relation for each variable, Vi, is stored
as a hash file with key, Ki, chosen as follows.
.bb
1) For each j select from the remaining multi-variable clauses in the query
the collection, C(ij), which have the form
.ti +8
Vi.di = Vj.dj  
.br
where di,dj are domains of Vi and Vj.
.br
2)  Form the key Ki to be the concatenation
of domains di1,di2,...of Vi appearing in clauses
in C(ij).
.br
3) If more than one j exists, for which C(ij) is non empty, one C(ij)
is chosen arbitrarily for forming the key.
If C(ij) is empty for all j, 
the relation is stored as an unsorted table.
.ph
.be
c)  Choose the variable, Vs, with the smallest number of tuples
as the next one for which to perform
tuple substitution.
.ph
d)  For each tuple variable Vj for which C(js)
is non null, reformat the storage structure
of the relation Rj which it ranges over, if necessary,
so that the key of Rj is the concatenation of
domains dj1,... appearing
in C(js). 
This ensures that when the clauses in C(js) become one-variable
after substituting for Vs, subsequent calls to OVQP to restrict
further the range of Vj will be done as efficiently as possible.
.ph
e)  Perform the following two steps for all
tuples in the range of the variable selected in (c):
.bb
1) substitute values from tuple into query.
.br
2) call decomposition algorithm recursively on a
copy of resulting query which now has been reduced by one variable.
.ph
.be
The following comments on the algorithm
are appropriate:
.ph
a)  OVD is almost always assured of speeding
processing.  Not only is it possible to
wisely choose the storage structure
of a temporary relation but also the
cardinality of this relation
may be much less than the one it
replaces as the range for a tuple variable.
It only fails if little or no
reduction takes place and
reformating is unproductive.

It should be noted that a temporary relation is created rather 
than a list of qualifying tuple-id's.  The basic tradeoff 
is that OVD must copy qualifying tuples but can remove duplicates 
created during the projection.  Storing tuple-id's avoids the copy 
operation at the expense of reaccessing qualifying tuples and 
retaining duplicates.  It is clear that cases exist where each 
strategy is superior.  The INGRES designers have chosen OVD because it 
does not appear to offer worse performance than the alternative, 
allows a more accurate choice of the variable with the smallest 
range in step c) above and results in cleaner code.

b)  Tuple substitution is done when necessary on the
variable associated with the smallest
number of tuples.  This has the effect of
reducing the number of eventual calls on OVQP.

c)  Reformatting is done (if necessary)
with the knowledge that it will replace a collection
of complete sequential scans of a relation by a 
collection of limited scans.  This
will almost always reduce processing time.

d)  It is believed that this algorithm
efficiently handles a large class of
interactions.  Moreover, the algorithm does not
require excessive CPU overhead to perform.  There are,
however, cases where a more elaborate algorithm is 
needed.  The following comment applies to these cases.

e)  Suppose that we have two or more strategies ST0, ST1, ... ,STn,
each one being better than the previous one but also requiring
a greater overhead.
Suppose we begin an interaction on ST0 and run it for an amount
of time equal to a fraction of the
estimated overhead of ST1.
At the end of that time, by simply counting
the number of tuples of the first
substitution variable which
have already been processed, we can get an
estimate for the total
processing time using ST0. If this is significantly
greater than the overhead of ST1, then we switch to ST1.
Otherwise we stay and complete processing the interaction
using ST0.  Obviously, the procedure can be
repeated on ST1 to call ST2 if necessary,
and so forth.  

The algorithm detailed in this section is ST0.  A more sophisticated algorithm
ST1 is currently under development and is discussed in [WONG76].
.se
5.2 ONE VARIABLE QUERY PROCESSOR (OVQP)
.ph
This program is concerned solely with the
efficient accessing of tuples from a single
relation given a particular one-variable query. 
The initial portion of this program, known
as STRATEGY, determines what key (if any) may
be profitably used
to access the relation, what the value(s) of that
key will be used in calls to the AMI routine "find", and
whether the access
may be accomplished
directly through the AMI to the storage structure of the
relation itself or if a secondary index on the relation should be used.
If access is to be through a secondary index then STRATEGY must
choose which ONE of possibly many indices to use.
.ph
Then, the tuples retrieved
according to the access strategy selected are processed
by the SCAN
portion of OVQP.  This program
evaluates each tuple against the
qualification part of the query, creates
target list values for qualifying tuples, and
disposes of the target list appropriately.
.ph
Since SCAN is relatively straightforward, we
discuss only the policy decisions made in
STRATEGY.
.ph
First STRATEGY examines the qualification
for clauses which specify the value of a domain,
i.e. clauses of the form:

	V.domain op constant
.br
where "op" is one of {=, <, >, <=, >=}.
Such clauses are termed "simple" clauses and are
organized into a list
.ph
Obviously a non-simple clause may be equivalent to a simple one.
.br
For example
	E.SALARY/2 = 10000 is equivalent to E.SALARY = 20000.
.br
However, recognizing and converting such clauses
requires a general algebraic symbol
manipulator.  This issue has been
avoided by ignoring all non-simple
clauses.  STRATEGY must now select one of
two accessing strategies:
.br
a)  issuing two AMI find commands on the primary
relation followed by a sequential scan of the
relation between the limits specified
.br
b)  issuing two AMI find commands on some index relation
followed by a sequential scan of the index
between the limits specified.  For each
tuple retrieved the "pointer" domain
is obtained and is a tuple-id of a tuple in
the primary relation.  This tuple
is fetched and examined.
.ph
Key information about the primary 
relation is obtained using
the AMI function "paramd".
Names of indices are obtained from the
index catalog and keying information about indices in obtained with
the function "parami".
.ph
STRATEGY now checks if a simple
clause is available to limit the scan of
the primary relation or an index relation.
If a relation is hashed the simple
clause must specify equality as the
operator in order to be
useful.  ISAM structures on the other hand
allow ranges of values and less than
all keys may be specified as long as
the first one is present for structures
with combined keys.
.ph
STRATEGY checks for such a simple clause for a relation in the following
order:
.bb
a.  hashed primary relation
.br
b.  hashed index
.br
c.  ISAM primary relation
.br
d.  ISAM index
.be
.in 0
The rationale for this ordering is related to the
expected number of page accesses required to retrieve
a tuple from the source relation in each case.
.ph
In case a) the key value provided locates a desired
source tuple in one access,
(ignoring overflows).  
In case b) the
key value locates an appropriate index relation
tuple in one access but an additional access in required to retrieve the proper
source tuple.  For the ISAM scheme, the
directory must be examined.  The number of accesses
incurred in this look-up is at least 2.
Again, with an index, 
an additional
access is required, making the total at least 3
in case d).
.bp
.fo 'DESIGN OF INGRES (VI)'-%-'12/5/75'
6  UTILITIES IN PROCESS 4
.se
6.1  IMPLEMENTATION OF UTILITY COMMANDS
.ph
We have indicated in Section 1 several data base utilities
available to users.  We will now briefly describe their 
implementation and indicate their configuration within the
INGRES system.
.ph
The commands are organized into several overlay programs.
Since an overlay may have more than one
entry point, it can contain
more than one utility command.
In fact, the utilities
are grouped where possible to minimize overlaying.
The overlays all contain a common main program known as
the "controller", which reads pipe C and writes
completion messages into pipe D.
The processing of a utility command occurs as
follows.
.ph
First, the parser recognizes a utility command in a user interaction.
This name is looked up in the INGRES "process-table",
which has an entry for each command name in the language.
Each entry has an "overlay-id" and a "function-id".
The first indicates the overlay program containing the
command, and, the second indicates the proper entry point
within that overlay.
.ph
These id's are passed down pipe B to process 3
followed by the parameters of the command specified.
Process 3 determines from the "overlay-id"
if the command is a utility command intended for process 4.
If so, the information is simply written on pipe C.
.ph
At this point, some overlay is occupying process 4, having remained
from a previous command.  Its copy of the controller
reads pipe C to obtain the overlay-id.
If a different overlay from the present one is
indicated, the controller overlays process 4 and
control passes to the controller of the new overlay.
.ph
Most of the utilities update or read the system
relations using AMI calls.  MODIFY contains a sort
routine which puts tuples in collating sequence
according to the concatenation of the
desired keys (which need not
be of the same data type).
Pages are initially loaded to approximately 80%
of capacity.  The sort routine
is a recursive N-way merge-sort
where N is maximum number of files process 4
can have open at once (currently 8).
The index building occurs in an obvious way.  To convert
to hash structures MODIFY
must specify the number of primary pages to be
allocated.  This parameter is used by the AMI in its
hash scheme (which is a standard modulo division method).
This is done by a rule of thumb.
.ph
It should be noted that a user who
creates an empty hash relation using the CREATE command and then
copies a large UNIX file into it using COPY
will create a very inefficient structure.  This is because
a relatively small default number of primary pages will have
been specified by CREATE and overflow chains
will be long.  A better strategy is
to COPY into an unsorted table so that
MODIFY can subsequently make a good guess
at the number of primary pages to allocate.
.se
6.2  DEFERRED UPDATE AND RECOVERY

Any updates (APPEND, DELETE, REPLACE) are processed
by writing the tuples to be added changed or modified into
a temporary file.  When process 3 finishes,
it calls process 4 to actually perform the modifications
requested as a final step in processing.  Deferred update
is done for four reasons.

a)  Secondary index considerations. Suppose the following
QUEL statement is executed;
.in 10
.ss

RANGE OF E IS EMPLOYEE
.br
REPLACE E(SALARY = 1.1*E.SALARY)  WHERE
.br
     E.SALARY > 20000
.ds
.in 0

Suppose further that there is a secondary index on the
salary domain and the primary relation is keyed on another domain.

OVQP in finding the employees who qualify for the raise
will use the secondary index.  If one employee (say Smith qualifies and his
tuple is modified and the secondary index updated) then the scan of the secondary
index will find his tuple a second time (in fact an arbitrary number of times).
Either secondary indexes cannot be used to identify qualifying
tuples when range qualifications are present (a rather
unnatural restriction) or secondary
indices must be updated in deferred mode.

.ph
b)  Primary relation considerations.  
Suppose the following QUEL statement is executed

.in 10
.ss
RANGE OF E, M IS EMPLOYEE
.br
REPLACE E(SALARY = .9*E.SALARY)  WHERE
.br
.in 15
E. MGR = M.NAME
.br
.in 17
AND
.br
.in 15
E.SALARY > M.SALARY
.ds
.in 0

for the following EMPLOYEE relation

.nf
		NAME    SAL     MANAGE  
.ss
		Smith   10k      Jones     
		Jones    8k                
		Brown  9.5k      Smith     
.fi
.ds
Logically Smith should get the pay cut but Brown should
not.  However, if Smith's tuple is updated before Brown
is checked for the pay cut, Brown will qualify.  This
undesirable situation must be avoided by deferred update.

c)  Functionality of updates.
Suppose the following QUEL statement is executed.

.in 10
.ss
RANGE of E,M is EMPLOYEE
.br
REPLACE E(SALARY = M.SALARY)
.ds
.in 0

This update attempts to assign to each employee
the salary of every other employee, i.e.
a single data item is to be replaced by multiple values.
Stated differently, the REPLACE statement does not specify a function.
This non-functionality
can only be checked if deferred update is performed.
.ph
d)  Recovery is easier.  
The deferred update file provides a log of updates
to be made.  Recovery is provided upon system
crash by the RESTORE command.
In this case the deferred update routine is requested
to destroy the temporary file if it has
not yet started processing it.
If it has begun processing, it reprocesses the
entire update file which is done in such a way that the
effect is the same as if it were processed exactly once from
start to finish.

Hence the update is "backed out" if deferred updating has not yet
begun; otherwise it is processed to conclusion.
The software is designed so the update file can be optionally spooled onto tape and
recovered from tape.  This added feature should soon be operational.

If a user from the terminal monitor (or a C-program)
wishes to stop a command he can issue a "break" character.
In this case all processes reset execept the deferred update
program which recovers in the same manner as above.

All update commands do deferred update; however the INGRES
utilities have not yet been modified to do likewise.
When this is completed INGRES will
recover from all crashes which leave the disk intact.
In the meantime there can be disk-intact crashes which
cannot be recovered in this manner (if they happen in such a
way that the system catalogs are left inconsistent).

The INGRES "super-user" can checkpoint a data base(s)
onto tape using the UNIX backup scheme.  Since INGRES
logs all interactions, a consistent system can always be
obtained (albeit slowly) by restoring the last checkpoint
and running the log of interactions  (or the tape(s)
of deferred updates if it exists).


.bp
.fo 'DESIGN OF INGRES (VII)'-%-'12/5/75'
7  CONCLUSION AND FUTURE EXTENSIONS

The system described herein is in use at 5
installations and is being brought up at 8 others.
It forms the basis of an
accounting system, a system for managing student records,
a geo-data system, a system for maintaining
a wiring diagram for a large telelphone company and assorted
other smaller applications.  These
applications have been running for periods of
up to nine months.

7.1  PERFORMANCE

At this time no detailed performance measurements have
been made.  However, on our system (an 11/40 mainframe with 80k words of
core) about 4-6 simultaneous INGRES users can be supported with
reasonable response time (assuming they are doing interactions which 
affect a small number of tuples and for which a fast access path 
exists.  Of course, a user has the ability to execute interactions 
in INGRES which require hours to process).  This hardware configuration
costs about
$60,000.  Larger 11/70 installations should be
able to run substantially more INGRES users.

The sizes of the processes in INGRES are indicated below.
Since the access methods are loaded
with processes 2 and 3 and with many of the utilities
their contribution to the respective process sizes has been noted separately.
.bb
access methods (AM)		11 K (bytes)
.br
terminal monitor		10 K
.br
EQUEL				30 K + AM
.br
process 2         		45 K + AM
.br
process 3 (query processor)	45 K + AM
.br
utilities (8 overlays)          160 K + AM

.in 0
7.2  USER FEEDBACK

The feedback from internal and external users
has been overwhelmingly positive.
In this section we indicate features that have been
suggested for future systems.

a)  higher performance

Earlier versions of INGRES were very slow.
The current version should alleviate this problem.

b)  recursion

QUEL does not support recursion.  Hence, recursion must be
tediously programmed in C using the precompiler.
This has been suggested as a desired extension.


c)  other language extensions

These include user defined functions (especially counters),
multiple target lists for a single qualification statement and if-then-else
control structures in QUEL.
These extensions are all so a user can avoid using the precompiler.

d)  report generator

PRINT is only a very primitive report generator.
The need for augmented facilities in this area is clear.
It should be written in EQUEL.

e)   bulk copy

The COPY routine fails to handle easily all situations that have arisen.

7.3  FUTURE EXTENSIONS

Noted throughout the paper are areas where
system improvement is in progress, planned or desired by users.
Other areas of extension include the
following

a)  A multi-computer system version of INGRES to operate
on distributed data bases

b)  Further performance enhancements

c)  A higher level user language including recursion and user defined
functions

d)  Better data definition and integrity features

e)  A data base administrator advisor.  This program would run at idle 
priority and issue queries against a statistics relation to be kept by 
INGRES.  It could then offer advice to a DBA concerning the choice of 
access methods and the selection of indices.  This topic is discussed 
further in [HELD75b].
.bp
ACKNOWLEDGEMENT
.ph
Besides the authors, the following
persons have played an active role
in the design and implementation of INGRES:
Eric Allman, Rick Berman, Jim Ford, Angela Go,
Nancy McDonald, Peter Rubinstein, Iris Schoenberg, Nick Whyte,
Carol Williams, Karel Youssefi, Bill Zook.
.ph
Support for the project has come from
ARO23007, DAHC04-74-G0087,
NESCN0039-76-C-0022,
NSFF44620-71-C-0087,
JSEPDCR75-03839, NSFENG74-06651-AO1,
and a grant from the Sloan Foundation.
.bp
REFERENCES
.sp 2
.in +9
.ti -9
ALLM76	
Allman, E., Stonebraker, M., and Held, G. 
"Embedding a Relational Data Sub-language in a General Purpose Programming Language.", 
Proc. ACM SIGPLAN-SIGMOD Workshop on Data, 
Salt Lake City, Utah, March, 1976.
.ti -9
ASTR76	
Astrahan, M. et. al., "SYSTEM R: A Relational Approach to
Data Base Management," TODS, Vol 1, No. 2.
.ti -9
BOYC73	
Boyce, R. et. al., 
"Specifying Queries as Relational Expressions: SQUARE", 
IBM Research, San Jose, Ca., RJ 1291, Oct. 1973.
.ti -9
CHAM74	
Chamberlin, D. and Boyce, R., 
"SEQUEL: A Structured English Query Language", 
Proc. 1974 ACM-SIGFIDET Workshop on Data Description, Access and Control, Ann Arbor, Mich., May 1974.
.ti -9
CHAM75	
Chamberlin, D., Gray, J.N., and Traiger, I.L., 
"Views, Authorization and Locking in a Relational Data Base System", 
Proc. 1975 National Computer Conference, AFIPS Press, May 1975.
.ti -9
CODA71	
Committee on Data Systems Languages, 
"CODASYL Data Base Task Group Report", 
ACM, New York, 1971.
.ti -9
CODD70	
Codd, E.F., 
"A Relational Model of Data for Large Shared Data Banks", 
CACM, Vol. 13 No. 6, pp. 377-387, June, 1970.
.ti -9
CODD71	
Codd, E.F., 
"A Data Base Sublanguage Founded on the Relational Calculus", 
Proc. 1971 ACM-SIGFIDET Workshop on Data Description, Access and Control, San Diego, Ca., Nov. 1971.
.ti -9
CODD72	
Codd, E.F., 
"Relational Completeness of Data Base Sublanguages", 
Courant Computer Science Symposium 6, May 1972.
.ti -9
CODD74	
Codd, E.F. and Date, C.J., 
"Interactive Support for Non-Programmers, The Relational and Network Approaches", 
Proc. 1974 ACM-SIGFIDET Workshop on Data Description, Access and Control, Ann Arbor, Mich., May 1974.
.ti -9
DATE74	
Date, C.J. and Codd, E.F., 
"The Relational and Network Approaches: Comparison of the Aplication Programming Interfaces", 
Proc. 1974 ACM-SIGFIDET Workshop on Data Description, Access and Control, Ann Arbor, Mich., May 1974.
.ti -9
GRAY75   Gray, J.N., Lorie, R.A., and Putzolu, G.R.
"Granularity of Locks in a Shared Data Base"
Proc. International Conference on Very Large
Data Bases, Framingham, Mass., September, 1975.
.ti -9
GO75	
Go, A., Stonebraker, M., and Williams, C., 
"An Approach to Implementing a Geo-data System", 
Proc. ACM SIGGRAPH/SIGMOD Conference on Data Bases in Interactive Design,
Waterloo, Ontario, Sept. 1975.
.ti -9
GOTT75   Gottlieb, D., et. al.  "A Classification of
Compression Methods and their
Usefulness in a Large Data Processing Center"
Proc. 1975 National Computer Conference,
AFIPS Press, May, 1975.
.ti -9
HELD75a	
Held, G.D., Stonebraker, M. and Wong, E., 
"INGRES - A Relational Data Base Management System", 
Proc. 1975 National Computer Conference, AFIPS Press, 1975.
.ti -9
HELD75b	
Held, G.D., 
"Storage Structures for Relational Data Base Management Systems", 
Ph.D. Thesis, Dept. of Electrical Engineering and Computer Science, Univ. of California, Berkeley, 1975.
.ti -9
HELD75c	
Held, G., and Stonebraker M., 
"B-Trees Re-examined", 
to appear in CACM.
.ti -9
IBM66	
IBM Corp., 
"OS ISAM Logic", 
IBM, White Plains, N.Y., GY28-6618.
.ti -9
JOHN74	
Johnson, S.C., 
"YACC, Yet Another Compiler-Compiler", 
UNIX Programmer's Manual, Bell Telephone Labs, Murray Hill, N.J., July 1974.
.ti -9
MCDO75a	
McDonald, N. and Stonebraker, M., 
"Cupid -- The Friendly Query Language", 
Proc. ACM-Pacific-75, San Francisco, California, April 1975.
.ti -9
MCDO75b	
McDonald, Nancy., 
"CUPID: A Graphics Oriented Facility for Support of Non-programmer Interactions with a Data Base", 
Ph.D. Thesis, Dept. of Electrical Engineering and Computer Science,
University of California, Berkeley, 1975.
.ti -9
RITC74	
Ritchie, D.M. and Thompson, K. 
"The UNIX Tine-Sharing System,"
CACM,
Vol. 17, No. 3., March, 1974.
.ti -9
SCHO75	
Schoenberg, Iris, 
"Implementation of Integrity Constraints in the Relational Data Base Management System, INGRES", 
M.S. Thesis, Dept. of Electrical Engineering and Computer Science,
University of California, Berkeley, 1975.
.ti -9
STON74a	
Stonebraker, M., "A Functional View of Data Independence,"
Proc. 1974 SIGFIDET Workshop on Data
Description, Access and Control, Ann Arbor, Mich., May 1974.
.ti -9
STON74b	
Stonebraker, M. and Wong, E., 
"Access Control in a Relational Data Base Management System by Query Modification", 
Proc. 1974 ACM National Conference, San Diego, Ca., Nov. 1974
.ti -9
STON74c  Stonebraker, M., "High Level Integrity
Assurance in Relational Data Base Systems", 
University of California, Electronics Research
Laboratory, Memo ERL-M473, August, 1974.
.ti -9
STON75	
Stonebraker, M., "Implementation of Integrity Constraints and
Views by Query Modification", Proc 1975 SIGMOD Workshop
on Management of Data, San Jose, Ca., May 1975.
.ti -9
STON76	
Stonebraker, M. and Rubinstein, P., "The INGRES Protection System,"
Proc. 1976 ACM National Conference, Houston, Texas, October, 1976.
.ti -9
TSIC75	
Tsichritzis, D., 
"A Network Framework for Relational Implementation", 
University of Toronto, Computer Systems Research Group Report CSRG-51, Feb. 1975
.ti -9
WONG76	
Wong, E. and Youssefi, K., 
"Decomposition-A Strategy for Query Processing,"
TODS, (this issue).
.ti -9
ZOOK76	
Zook, W., et. al.,
"INGRES - Reference Manual (Version 5)",
University of California, Electronics Research
Laboratory, Memo. No. ERL-M585, April, 1976.
