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AlllQH mOQSD NBSIR 81-2302

^.le Positional Set Processor:

A Tool for Data Modeling

MBS

PUBLICATIONS

W. Terry Hardgrave

Sandra B. Salazar

National Bureau of Standards

Institute for Computer Sciences and Technology

Washington, D. C.

The Positional Set Processor (PSP) is a

software tool for manipulating mathematical objects such as sets, sequences, ordered pairs, etc.

The PSP serves as the underpinning for a Data

Model Processor (DMP), an experimental system for

emulating commercial and protorype database

management systems. The PSP also provides a mathematical basis for semantic specification and

interpretation of database operations. Vvhile its

powerful query facilities make the PSP itself appear to be a database managem.ent system, it has no

explicit concept of data definition, no access

control, no integrity control, ere. Tne authors

prefer to viev7 the PS? as a tool for specifying

and building database managem.ent systems . This

paper reviews the mathematical form.alism, Positional Set Notation, and describes the design of

the Positional Set Processor.

30 November 1981

A.bstract

lUG

1 U56

cil-2302

1931
1 INTRODUCTION

Data models may be

nings for database man

Database Models Project

(NBS) is developing

data models. One objec

implement a Data Mod

that will accept a desc

the behavior of an im

is, a particular DBMS),

term "data model" is

specification for a dat

teristics

viewed as the theoretical underpinagement systems (DBMS). The Abstract

at the National Bureau of Standards

a structured approach to the study of

project is to design and

(DMP), a software system

data model and emulate

of that data model (that

a precise definition of the

evolving, we believe that a

tive of this

el Processor

ription of a plementation

While

still

a model should have these characIt should include specifications for data structures

(e.g. trees, networks, relations, etc.) pi us specifications for operations (e.g. find-record, join,

etc.) on those data structures.

It should account for both structures used for definitional purposes and structures that appear as

occurrences in the database. It may also include

structures used for secondary indexing if the fundam.ental operations depend on those structures.

It should be documented in the open literature, independently of any vendor's literature.

* It should

framework

semantic s

be stipulated in a formal

that. requires rigorous

as v/ell as syntax.

or mathematical

specification of

An important concept in the DMP framework (v/hich is

consistent v;ith denotaticnal semantics [JONE78]) is that the

concepts of a data model can be expressed as set- theoretic

objects. Thus, we have chosen to express the data structures as "positional sets" and the operations as operations

on positional sets. This paper deals with the mathematical

formalism for expressing positional sets, called Positional

Set Notation (PSN), and a major component of the DMP, the

Positional Set Processor (PSP), a sophisticated tool for

storing and retrieving positional sets.

- 2 -
2 SUMMARY OF POSITIONAL SET NOTATION (PSN )

The philosophy behind Positional Set Notation is similar to the philosophy behind the Vienna Definition Method

(VDM)--see [JONE78]. That is, the semantics of operations

(i.e. functions, processes, etc.) programmed in computer

languages should be defined in terms of abstractions that

are divorced from physical implementations. These abstractions are, in turn, defined in a mathematical notation. The

VDM approach uses (with a few minor exceptions) traditional

mathematical notation and list structures. In this work, we

use PSN.

PSN provides sufficient expressive power to define a wide range of data models. One salient feature is the availability of the "labeled tuple" which is the mathematical

counterpart of an ADP "record" and simplifies the definition

of most data models. This section provides an informal summary of PSN; more detail may be found in [HARDSla]

The essence of PSN is the recursive definition of the

positional set, S:

S := [x(l)@p(l), x(2)@p(2), ..., x(n)@p(n)]

where

* the p{ i) are called position identifiers and must be

atoms, that is, either numbers or character strings.

The p(i)'s need not be unique.

* the x(i) are el ements and may be either atoms or

themselves posirional sets.

The mathematical object S, above, is a mathematical set of

ordered pairs. Vie surround it with square brackets rather

than braces for reasons discussed below. For convenience,

the construction "x(i)(sp(i)" is called a "duplex". Duplexes

may appear in any order in the written representation of a positional set.

An example of a positional set (abbreviated as "p-set")

in which all of the elements are atoms is:

[JONES0NAME, 25 0AGE, UMD(?SCHOOL, BA(?DEGREE]

Here the elements are JONES, 25, UMD, and BA. The

position_identif ier s (pids) are NAME, AGE, SCHOOL, and DEGREE. An example of a p-set in which some of the elements

are themselves p-sets is the p-set "STUDENT":

3 -
[[ [ [JfeMI, JONES0LAST, JOHN0FIRST](a# ](3NAME, 25@AGE,

[ [UMDC^SCHOOL, BA0DEGREE,

[ [CMSC410@COURSE, B(3GRADE ]@# , [CMSC420(§COURSE, A0GRADE ]@# ] @CURRIC]@# ] @ED_HIST](§# , [ [S(3MI , SMITHgLAST, SCCTTlsFIRST ] 0NAME, 29 @ AGE , [ [UNC0SCHOOL, PHD(oDEGREE,

[ [CMSC6200COURSE, A@GRABE ]@#

[CMSC6300COURSE, A0GRADE ]0#

[CMSC79S0COURSE, A0GRADE ]@#

[CMSC720 0COURSE, B0GRAEE ]0? ] @CURRIC]0? j 0ED_HIST]@# J The symbol 4 denotes the null position identifier. Given in

tabular form with the position identifiers as column

headers, the p-set above looks like;

STUDENT

NAME AGE ED_HIST

FIRST MI LAST SCHOOL DE GREE CURRIC

COURSE GRADE

JOHN J JONES 25 UMD BA CMSC410 B

CMSC420 A

SCOTT S SMITH 29 UNC PHD CMSC620 A

CMSC630 A

CMSC798 A

CMSC720 B

The PSP described here has print operations that display psets in tabular form as well as the formal bracketed notation; both forms are shov/n above.

PSN allows the data modeler to use and m.anipulate a number of objects similar to traditional m.athemat ical objects. The p— sets representing the classical set, the ordered pair, the sequence, and the labeled tuple are shown in

the table below. As mentioned above, the square brackets

are used to surround p-sets so the braces can be used to

surround classical sets (i.e., sets in which all the pids

are '*#") . Ihe PSP will accept mathematical objects in either the traditional notation or PSN. All traditional expressions are converted to PSN. The mathematical underpinning is explained in detail in [HARBSla]

-4-
OBJECT TRADITIONAL

REPRESENTATION

POSITIONAL SET

NOTATION

CLASSICAL

SET

SEQUENCE <a( 1 ) ,a ( 2 ) t

• * • t a(n)> [ a( 1 )$1 , a ( 2 ) 02 , . . . , a ( n) @n]

ORDERED (a,b) [ a01 , b02

]

PAIR

2-ELEMENT <a,b> Ca01,b02]

SEQUENCE

The labeled tuple is an important concept found in most

data models and the basis for the relational model:

C( 1 ) C( 2 ) ... C( n)

a(l) a(2) ... a(n)

The C( i) are column-headings and a(j) are atomic elements;

this is represented in PSN as

[a(l )0C(1 ),a(2)0C(2), . .

. ,a(n)0C(n)]

Following is an example of a relational database expressed first in the tabular form of [ZL0075], then in PSN

using the relational formulation given in [KARD7S].

Tabular form:

SALES DEPARTMENT ITEM

STATIONERY

HOUSEHOLD

STATIONERY

COSMETICS

TOY

TOY

TOY

COSMETICS

STATIONERY

HARDWARE

DISH

PEN

PENCIL

LIPSTICK

PEN

PENCIL

INK

PERFUME

PEN

INK
TYPE ITEM COLOR SIZE

DISH WHITE M

LIPSTICK RED L

PERFUME WHITE L

PEN GREEN S

PENCIL BLUE M

INK GREEN L

INK BLUE S

PENCIL RED L

PENCIL BLUE L

In PSN form, the set of relation occurrences, REL-OCC, is:

[ [SALES® REL_NAME, [ [STATIONERY^DEPARTMENT , DISH@ITEM ] @#

[HOUSEHOLDGDEPARTMENT, PEN(§ITEM ] §# ,

[ HARDWARE (2DEPARTM ENT, INK@ITEM ] @ RELATION ] 0# , [TYPE0REL_NAME, [ [DISH0I TEM , WHITE 0COLOR, M@S I ZE ] 0#

[LIPSTICK0ITEM, RED0COLOR, L0SIZE]0#

[PENCIL0ITEM, BLUE0COLOR, L0SIZE]0# ] 0RELATION ] 0#

]
3 . AN OVERVIEW OF THE POSITIONAL SET PROCESSOR

The Positional Set Processor (PSP) is a collection of

37 commands (see Table 1). These commands are operations on

positional sets; most commands take p-sets as input and produce p-sets as output. They are not intended to comprise a

convenient high level query language.

The development of the PSP is part of an experimental

project and the collection of commands has been modified as

the Data Model Processor (DMP) design has proceeded. V^e began v/ith a basic set of Classical Set Operations (such as

union, intersection) that, when applied to positional sets,

are analogous to the traditional set operations. The

Utility Operations (such as print, copy) provide additional

capabilities needed for use in an interactive environment.

Tlie Positional Set Operations provide the user with the

basic database funcrions--retr ieving , updating, adding, and

deleting. The operation "CREATE" is the most important

operation and is analogous to the relational DBMS operations

"Retrieve" in QUEL or "SELECT" in SQL. There are also

operations to return the (classical) set of elements, return

the (classical) set of po sition_identi f ier s for a p-set, and

distribute a posi tion_identi f ier over a classical set. TEMPLATE, POPULATE, and CONFORM were designed specifically for

use by the various DMP roles.

Since some data models (e.g., CODASYL ) require the

manipulation of sequences, the Sequence Operations were added to allow manipulation of sequences as a special form of

p- sets . We will not attempt to fully describe all

mands in this paper, but w'ill concen

group, the Positional Set Operations. A

tion of the ccminands ( including both s can be found in "The Positional Set Proc

es of the use of th

[KOLL82 ]

:he PSP com-

[HARDSlbJ and exampl

given in [K0LL81] and

trate on the cen tral

complete desc ripyn tax and s emant ic s

essor User' s Ma n ual"

e PSP by th e DMP are

- 7 -
TABLE 1 PSP COMMANDS

Classical Set Operations

IN Intersection

UN Union

RC Relative Complement

SY Symmetric Difference

CD Cardinal ity

Positional Set Operations

CR Create

RG Range

FR Freeze

ST Start

RL Release

TH Thaw

Extended Positional Set Operation

BR Break

RK Recur se

TMP Tempi ate

POP Populate

CNF Conform

Sequence Ope rations

SQ CAT Concatenate sequence

SQ EXC Extract by contents

SQ EXI Extract: by index

SC FLC Flush by contents

SQ lAC Insert after content

SQ lAI Index after index

SQ IBC Insert before conten

SQ_RPC Replace element

Utility Oper ations - Non-predicat

CP Copy

DE Delete

NS Null set

. PT Put

EN Enter

PN Print names

PS Print set

Utility Oper ations - Predicates

CS Classical set

EC Equal

I SIN Is in

NL Null

NN Not null

SB Sub set

- 8 -
4 . POSITIONAL SET OPERATIONS

The Positional Set Operations (CREATE, RANGE, FREEZE,

START, RELEASE, and THAW) allow traversal of p-sets and generation of new p-sets based on a specified condition. In

this section we will discuss "range variables" and the "dot

operator" and will then describe the commands.

Rang e Variables

Range variables ( rv) allow access to p-sets. The name

"range variable" is taken from ALPHA [C0DD71 ] and QUEL

[STON76], but the concept is more general here. Unlike (normalized) relations, p-sets may be nested to any depth. The

range variables provide a mechanism for accessing nested

structures as well as first normal form relations.

Each rv is associated with a particular p-set. That

is, the declaration of a range variable enables that variable to take on, one- at- a- time and in no particular order,

the values of the elements of a p-set. If X is a variable

ranging over the p-set P, then "print all X" would print all

the elements of P. The qualification, "X = <value>" is TRUE

iff 9X (X P AND X = <value>). Thus, "print all X where

<condition>" would print those elements of P which satisfy

< condition> .

The association between the p-set and the rv is established with the RANGE command and (unlike QUEL) remains in

effect until cleared by the RL or ST command ( see below)

Dot Operator

The dot operator, often used without formal definition,

has been a mainstay for several relational languages (e.g.

QUEL, SEQUEL2), as it is quite useful in designing query

languages with substantial expressive power. It is also a

rotational device to simultaneously allow traversal of a set

and access to (elements of) tuples within the set. Since

both the tuples and the sets can be represented as p-sets, a more precise definition of the dot operator expression can

be given in PSN.

Let X range over the p-set P. At any particular time,

X is a pseudon^^m for a tuple T that is an element of P. The

construction: "X.ATT" refers to the element at pid ATT contained in the tuple T. "Print all X.ATT" would print all

the values, Y, such that Y@ATT is an element of an elem.ent

of P. That is:

"X.ATT = <value>" is TRUE iff

- 9 -
dY (Y(sATT i T AND T ( P AND Y = <value>).

For example, consider the <condition>;

X.AGE = 21

as evaluated for a particular value of X ( ie . , some elemen

of P). The <condition> is TRUE if "21@AGE" is an element o

X ( ie . , an element of an element of P). Similarly, the

< cond ition>

X.AGE > '30'

returns TRUE if there exists an M such that "M0AGE" is an

element of X and M > '30'.

Command s on Range Variables

The START (ST) command initializes the global range

variable by deleting all range variable associations.

The RANGE (RG) command declares and associates a range

variable with a p-set. It has two forms;

RG <rv> IS <p-set name>

or

RG <rvl> IS <rv2> . <pid>

For example, the command:

RG X IS STUDENT

declares "X" a range variable and associates it with the

p-set named "STUDENT". The rv "X" ranges over the duplexes

of the p-set "STUDENT".

The command form to declare and associate an rv with a p-set element (that is itself a p-set) is somewhat more complex. The dot operator indicates that the <pid> is at

the next level of nesting within the p-set or p-set element

associated with < rv2 > . For example, the command;

RG Y IS X.ED_HIST

declares "Y " a range variable and associates it with the

element X w'hich has pid "ED_HIST". "ED_HIST" is at the next

level of nesting within the p-set over which "X" ranges,

that is, "STUDENT".

-10 -

Hi

ft-
Declaring one range variable in terms of another implies a relationship between range variables that is important for the semantics of the CREATE command; this is an

ancestor relationship. If X is an rv and appears in an RG

statement

RG X IS <p-set name>

then X has no ancestors. If Z is an rv and appears in a statement

RG Z IS Y.<pid>

then Y is both an ancestor and the parent of Z., All of Y's

ancestors are also ancestors of Z. In the example:

RG X IS STUDENT

RG Y IS X.ED_HIST

RG Z IS Y.CURRIC

"X " has no ancestors; "X" is an ancestor of "Y" and "Z" and

the parent of "Y"; "Y

is an ancestor and the parent of "Z".

The RELEASE (RL) command, which has the form:

RL <rv>

removes the association between the specified rv and a pset

The FREEZE ( FR ) command binds the rv to one duplex of

the p-set for which the specified <condition> is true. This

means that the rv no longer ranges over the entire p-set,

but indicates only one duplex. The form of the FREEZE command is:

FR <rv> WHERE <condition>

The rv must have been previously associated with a p-set using an RG command. The <condition> is a pr ed icate-- an expression involving comparison operators, boolean operators,

and parentheses, that returns "true" or "false". For example, the command:

FR X WHERE "X.AGE = *29’"

indicates that the rv "X" ranges over the duplexes in the

p-set with v/hich it is associated. Wlien a duplex that satisfies the condition (that the value of the elem.ent associated with the pid "AGE" is '29') is found, the value of the

rv "X" is then frozen at (i.e. bound to) that duplex. If

the condition is never satisfied, the rv remains free.

- 11 -
If an rv is frozen with the FREEZE command, all of its

ancestors will be frozen also. For example, if the unfrozen

rv ' s "X", "Y", and "Z" are associated with the p-sets "STUDENT”, "X.ED_HIST", and "Y.CURRIC", respectively, the comm^and ; FR Z WHERE " Z . COURSE= ' CMSC798 ' "

will not only freeze "Z" at a duplex in the p—set element

"Y.CURRIC" v/nich has 'CMSC798' as the value of the element

associated with the pid "COURSE", but will also freeze "Y

and "X" at the duplexes which are their values when the condition on "Z" is satisfied.

Note that when more than one duplex satisfies the condition, the choice of a duplex is impl smientation-dependent

and cannot be anticipated or controlled by the user. The

capability to traverse the p-set, successively freezing on

each duplex that satisfies the condition, is an option.

The THAW (TH) ccm.mand , which removes the FREEZE binding, has the form:

TH <rv>

\^7hen an rv is thawed, any frozen descendants are also

thawed; ancestors are not affected. Thus in general, the

"TH X" command is not the reciprocal of the " FR X" command.

The CREATE Command

The PSP CREATE ( CR ) command is analogous to SELECT in

the SEQUEL language of SYSTEM R [ASTR76] or RETRIEVE in the

QUEL language of INGRES [STON76]. How’ever, unlike SEQUEL

and QUEL, the PSP allov/s nested relations. In relational

jargon, this means that first normal form (INF) is not required. The CREATE command builds a new p-set having (1)

the specified attributes from the original p-set(s) and (2)

the duplexes which satisfy a given condition. It has the

form

CR P V7ITH < attribute- list> WHERE <condition>

The <condition> has the same form and meaning for the CREATE

command as for the FREEZE command. 'The < attribute- list> defines the structure of the new p-set by identifying its

pids. Syntactically, it is a list of < terra> '

and

< ass ig nmen t> ' s . A <term> specifies which pids are to be

taken from which p-sets; the basic form is:

"

< rv> .

pid> "

- 12 -
The < assignment> has the form:

"<pid> := <phrase> "

This allows the user to specify a pid for the nev/ p-set

which is not related to a previously defined p-set and to

assign a value for its element. The <phrasc> may be an arithmetic expression, a value, or a basic <term>. To rename

the pid in the new p-set, this form of the <assignment> is

used ; "<pid> := <rv>.<pid>"

An example of the CR command using our sample database

is

RG X IS STUDENT

RG Y IS X.ED_HIST

RG Z IS Y.CURRIC

CR NEV'JSET WITH "X . NAME , X . AGE , CLASS := '1981',

TRANSCRIPT := Y.CURRIC" WHERE "Y. DEGREE = 'PHD' i (Z. COURSE = 'CMSC498' & Z . GRADE = 'A')"

In the "WHERE" clause, "1 " is the logical "OR" operator and

"Sc" is the logical "AND" operator. The p-set "NEWSET" will

have the pids "NAME", "AGE", "CLASS", and "TRANSCRIPT".

"NAME" and"AGE" will be the same as in "STUDENT", and "TRANSCRIPT" will be the same as "CURRIC" in "STUDENT" (only the

pid name is different) . Each duplex will have the new pid

"CLASS" v/hich has the element value '1981'. The duplexes

chosen from "STUDENT" are those v/hich have 'PHD' as the

value of "DEGREE" or that have a duplex in "CURRIC" wit

'CMSC498' as the value of "COURSE" and 'A' as the value o

"GRADE". The ansv/er to this query, given the p— set "STUDENT" of section 2, would be:

PSN form:

[[[S@MI, SMITH @LAST, SCOTT @FI RST ] @NAME, 29(?AGE, 1981t2ciASS,

[ [CMSC6200COURSE, A0GRADE ](2# , [CMSC63G&COURSE, AiSGRADE ]y# , [CMSC79S(§COURSE, AGGRADE ]e# , [CMSC720(3COURSE, DEGRADE ]0# J ^TRANSCRIPT ] 0# ]

- 13 -
Tabular form:

NEWSET

NAME AGE CLASS

LAST FIRST MI

TRANSCRIPT

COURSE GRADE

SMITH SCOTT S 29 1981 CMSC620 A

CMSC630 A

CMSC798 A

CMSC720 B

Notice the similarity in the QUEL equivalent of this

CREATE statement:

RETRIEVE INTO NEWSET

(AGE=X. AGE , M\ME=X. NAME, TRANSCRIPT =Y . CUT.RIC , CIi\SS= "1 981 ")

WHERE Y. DEGREE="PHD" OR

( Z.COURSE="CMSC498 " AND Z . GRADE =

" A"

Since the PSP was designed to contain the functionality

of the relational operators, it is appropriate to discuss

how the relational operarors (i.e. PROJECT, SELECT, and

JOIN) as well as p-set operators can be expressed in terms

of the CREATE command. A_n informal discussion and some examples are given here.

A PROJECT can be represented as a CR with no' <condition> , with the effecc that each duplex of the original pset is selected, but only the pids specified in the

attribute- list are copied. For example,

RG X IS STUDENT

CR AGES WITH "X.AGE"

creates the p-set "AGES" which is a classical set containing

all the elements with pid "AGE" in the p-set "STUDENT".

PS N f o rm :

[[25 (SAGE J (3# , [ 2 9 (SAGE ] 0 # ]

- 14 -
Tabular form:

AGES

AGE

25

29

A slightly more complicated example is a PROJECT involving a nested pid

RG X IS STUDENT

RG Y IS X.ED__HIST

CR SCHOOLS WITH "Y. SCHOOL"

This creates the p-set

all elements with the

the p-set "STUDENT",

eliminated, since a p-

"SCHOOLS", a classical set

pid "SCHOOL" at the "ED_HIST

Any duplicate duplexes are,

set is a mathematical set.

containina

" level o

of course.

PSN form:

[[UMD(5SCH00L]@# , [UNC 0 SCHOOL ]@^tt ]

Tabular form:

SCHOOLS

SCHOOL

UMD

UNC

A SELECT can be expressed as a CR which copies each duplex of a p-set that satisfies a condition. For example,

RG X IS STUDENT

RG Y IS X.ED_HIST

CR DOCTORS WITH "X . NAME , X . AGE , X . ED_HI ST " VvHERE

"Y. DEGREE='PHD '

This creates a p-set "DOCTORS" having the same srructure as

the original p-set "STUDENT" but a subset of the original

duplexes-- those that satisfy the condition that 'PHD' is the

value of the element with pid "DEGREE" at the "ED_HIST" level .

-15 -

;i

4-1
PSN form:

C[[S@MI, SMITH@LAST, SCOTT (3FIRST ] 0NAME, 29@AGE,

[ [UNC@SCHOOL, PHD13DEGREE,

[ [CMSC620C^COURSE, A0GRADE ]@# , [CMSC6300COURSE, A0GRADE

[CMSC79S0COURSE, A0GRADE ]0#

[CMSC7200COURSE, B0GRADEJ0# ]@CURRIC]@# ]0ED_HIST]0^^ ]

Tabular form:

DOCTORS

NAME AGE

FIRST MI LAST

ED HIST

SCPiOOL DEGREE CURRIC

COURSE GRADE

SCOTT S SMITH 29 UNC PHD CMSC620 A

CMSC630 A

CMSC798 A

CMSC720 B

A JOIN can be expressed as a CR which concatenates duplexes from two p-sets, based on a condition that links the

p-sets through some pids that presumably have the same

domain. For example, given the p-set "ADDRESS":

PSN form:

[[ [S0MI, SMITK0LAST, SCOTT0FIRST ] 0PERSON , RALE IGH 0CITY , NC@STATE]0#

[ [J0MI, JONES0LAST, JOHN0FIRST]0PERSON, PITTSBURGH 0CITY, PA0STATE]@

Tabular form:

ADDRESS

PERSON CITY STATE

FIRST MI LAST

SCOTT S SMITH RALEIGH NC

JOHN J JONES PITTSBURGH PA

- 16 -
Tb.e PSP cominands:

RG X IS STUDENT

RG S IS ADDRESS

CR COMPLETE VJITH "X . NAME , X . AGE , X . ED_H I ST , S . C ITY, S . STATE " WHERE "X. NAME=S . PERSON"

create the p-set "COMPLETE" which consists of all concatenations of a duplex from "STUDENT" and a duplex from "A.DDRESS"

containing the same value of the elements corresponding to

pid "NAME" in "STUDENT" and pid "PERSON" in "ADDRESS". The

answer to this query, given the example "STUDENT" database,

is : PSN form:

[[ [J@MI, JONES0LAST, JOHN0FIRST](3NAME, 25 0AGE,

[ [UMD0SCHOOL, BA0DEGREE,

[ [CMSC4100COURSE, B0GRADE ]@#

[ CMSC420 0COURSE , A0GRADE ] 0# ] 0CURRIC ] 0# ] 0ED_H 1ST

PITTSBURGH 0CITY, PA0STATE]0#

[ [S0MI, SMITH0LAST, SCOTT 0FIRST ] 0NAME , 290AGE,

[ [UNC0SCHOOL, PHD0DEGREE,

[ [CMSC6200COURSE, A0GRADE ]0#

[CMSC6300COURSE, A0GRADE ]0#

[CMSC7980COURSE, A0GRADE ]0#

[CMSC720 0COURSE, B0GRADE J0# ] 0CURRIC]0# ] 0ED_HIST,

RALEIGH0CITY, NC0STATE]0#

]

Tabular form:

COMPLETE

NAME AGE ED__HIST CITY STATE

FIRST MI LAST SCHOOL DEGREE CURRIC

COURSE GRADE

JOHN J JONES 25 UMD BA CMSC410 B PITTSBURGH PA

CMSC420 A

SCOTT S SMITH 29 UNC PHD CMSC620 A RALEIGH NC

CMSC630 A

CMSC798 A

CMSC720 B

-17 -
5 CONCLUDING REMARI^S

The first version of the PSP is operational in an experimental environment. The system is quite slow and only

works with very small databases; so far, little v/ork has

been done on performance improvement. This section

discusses the success of the design and our plans for the

future

The PS P and Data Models

As mentioned earlier, the PSP is intended to be used as

a tool for studying DBMS’s, not as a DBMS itself. It has no

data definition facility, nor any restrictions on database

design, as would exist in a commercial DBMS that implemients

a particular data m^odel . However, unlike most tools, the

PSP has a tremendously powerful query facility. Consequently, iz. is useful to compare the expressive capabilities of

the PSP to those of various data models.

Th query language of the PSP may be viewed as an extension of relational query languages. Range variables,

similar to those in QUEL, enable referencing of attributes

in a relation. The basic data retrieval and manipulation

command, CREATE, is analogous to SELECT in SYSTEM R. However, the PSP has somie important features that extend its expressive pov/er beyond that of currenr relational systems.

* It allows nesting of all kinds of m.athematical objects within one another: sets, sequences, relations, or any other structures definable in PSN.

* There are no intrinsic normal forms. Normal forms

are restrictions on the original mathematical concept of a relation. The proliferation of normal

forms as anomalies or limitations are discovered in

each new one suggesrs that normalization is not

v/orth the sacrifice of the power of the mathematical

definition of "relation".

* The database may contain nested hierarchical structures that can be referenced with r el ational- like

command s

* Nodes from different subtrees can be specified in

the same query.

Thus, the PSP combines concepts from several data models and

serves as a powerful underpinning for the Bata Model Processor and as a basis for the study of future database management systems.

- 18 -
Future Directions

Project efforts in the next year are directed toward

applications of the Data Model Processor to such areas as

data model mappings, commercial DBMS validation, evaluation

of data model specifications, and query language translation. A paper on the DMP [KOLL82] is forthcoming. Work

will also be done on improving the efficiency and expressive

power of the PSP, so that it will be a more effective and

efficient tool. Some of our plans are discussed below.

Another version of the PSP, based on the same users

manual, but using an integer set processor (ISP), may be implemented. This would be similar to a previous implementation described in [HARD76]. The ISP has the potential to

perform set operations rapidly on rather large classical

sets of positive integers represented by bit strings. A revised bit- string technique has been developed by Gallagher

[GALL81]. By mapping p-sets onto the integers (using an

element table and the Cauchy-Cantor technique), the power of

an ISP can be used to implement p-sets.

Measurement and predictive performance modeling techniques may be used to direct the further developm.ent of the

prototype PSP. A new predictive model that handles both recursive routines and multiple concurrent processes may be

designed, implemented, and used to gather data on the execution of the major routines of the PSP. Eased on the

results, a model, similar to [DEUT78], that predicts performance for the prototype may be attempted . The model v/ould

be validated by checking predictions against actual performance in test cases, then the model would be used to forecast performance in an operational environment. Modification and optimization efforts would concentrate on the PS?

routines that the model shows to be problem areas.

The expressive power of the PSP will

modifications to some of the commands and

tional features for creating and accessing

will be specified.

be increased by

operators. A*ddinested structures

We will be examining the relationship between the PSP

and other work on semantics, abstract data modeling, and

functional languages. We are trying to incorporate some

ideas from functional languages [BACK80] but this is just

beg inning

- 19 -
6 AC KN OW LE DGEM ENT S

A major part of the design work on the PSP and DMP has

been done by Drs . M. Roll and G. Sockut . The implementation

(and some design) has been carried out by these part-time

and student programmers: Edwin J. Beller, Charles Haas,

Jerald Herstein, Thomasin Kirkendall, Anthony Marriott,

Joseph Naputi, Steven Norman, Sabrina Saunders, Michael

Shon, Cr is tine Shuey, and George Ski liman.

7. REFERENCES

ASTR76 Astrahan, M. M., et al . , "System R: Relational

Approach to Database Management", ACM Transactions

on Database Svstems, Vol . 1, No. 2, June 1976, pp

97-137.

BACKS0 Backus, J. , "Can Programming Be Liberated from the

von Neumann Style? A Functional Style and Its

Algebra of Programs" , Communications of the ACM , Vol. 21, No. 8, August 1978, pp . 613-641.

C ODD 71

DEUT78

Codd, E. F., "A Data Base Sublanguage Founded on

the Relational Calculus", Proceed ing s of the 19 71

ACM- S IGF IDET Workshop on Data Description , Access , and Control , Nov. 1971, ACM, New York, 1971, pp

35—68

Deutsch, D

Techniaues

Model ing and Measur emenor Evaluation of Desian Alternarives

in the im.Dl emen tar ion Da tabas< Manaa ement

Soft’ware, ITiS Special Publication 500-49, 19/8.

GALL81 Gallagher, L. , "Comiputer Im.pl ementation of an Integer Set Algebra" , N'BS Special Publication ( in

preparation), 1981.

- 20 -
HARD76

. HARD78

HARDSla

HARDSlb

JONE78

K0LL81

KOLL82

KURA76

STON76

ZL0075

Hardgrave, W. T. , "A Technique for Implementing a Set Processor", Con ference on Data ; Abstraction , Definition, and Structure, ACM, N.Y., 1976, pp

8-94.

Hardgrave, W. T. , "The Relational Model: A Reformulation of Some Mathematical Aspects Using Positional Set Notation", IFSM T.R. No. 25, University

of Maryland, 1978.

Hardgrave, V^/ . T. , "Positional Set Notation", to

appear in Advances in Database Manag ement , Vol . Heyden and Son, New York, 1981.

Hardgrave, W. T. , et al ."The Positional Set Processor User's Manual", NBSIR (in preparation),

1981 . Jones, C. B. and D. Bjorner (eds.)

The Vienna

Development Me thod : The Meta-Lang uag

, SpringerVerlag, New York, 1978.

Koll, Matthew, "Data Model Processor User's Manual", NBSIR (in preparation). National Bureau of

Standards, Washington, D. C., 1981.

Koll, Hatthev; B., Hardgrave, W. Terry, and Sandra

B. Salazar, "Data Model Processing", submitted to

NCC, Houston, Texas, May, 1982.

Kur atov/ski , K. and A. Mostowski , Set Theory , North-Holland Publishers, New York, 1976.

Stonebraker, M., E. Wong, et . al .

"The Design and

Implementation of INGRES" , ACM Transactions on

Database Systems , Vol. 1, No. 3, September 1976,

pp . 189-222.

Zloof, M.M., "Query-By-Exampl e" , Proceed ing s of

the’ AFIPS National Computer Conference Vol . 44,

AFIPS Press, Montvale, N.J. (May 1975) pp

431-438.

- 21 -
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NBS-n4A I REV. 2 -ec) U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

SHEET (See instructions)

REPORT NO.

NBS-IR-81-2302 Nov. 30, 1981

4. TITLE AND SUBTITLE

The Positional Set Processor: A Tool for Data Modeling

5. AUTHOR(S)

W. Terry Hardgrave, Sandra B. Salazar

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZiP)

Institute for Computer Sciences & Technology

Data Management & Programming Languages Division

National Bureau of S tandards/DoC/Bldg . 225, Room A265

Washington, DC 20234

10.

SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography nr litpraturesurvev. mention it here)

The Positional Set Processor (PSP) is aj

software tool for manipulating mathematical objects such as sets, sequences, ordered pairs, etc.

The PSP serves as the underpinning for a Data

Model Processor (DMP), an experimental system for

emulating commercial and prototype database

management systems. The PSP also provides a

mathematical basis for semantic specification and

interpretation of database operations. hbile its

powerful query facilities mtake the PSP itself appear to be a database management system, it has no

explicit concept of data definition, no access , control, no integrity control, etc. Tne authors

prefer to view the PSP as a tool for specifying

and building database management system.s. This

paper reviev;s the m.athemat ical formalism, Posi- | tional Set Notation, end describes the design of'

the Positional Set Processor.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize oniy proper names; and separate key words by semicolons)

databases, software tool, DBMS, database management systems

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

Unlimited For Official Distribution. Do Not Release to NTIS

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

22

15. Price

iy

Order From National Technical Information Service (NTIS). Springfield, VA. 22161

uscomm-dc 60o-per
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