SEQUEL- A structured English query language

Shawn.W潇

322

16页

4次

2022-11-01

免费下载

SEQUEL: A STRUCIURED ~NGLISH QUERY LANGUAGE

Donald D. Chamberlin

Raymond F. Boyce

IBM Research Laboratory

San Jose, California

ABSTRACT: In this paper we present the data manipulation facility for a

structured English query language (SEQUEL) which can be used for accessing

data in an integrated relational data base. Without resorting to the concepts

of bound variables and quantifiers SEQUEL identifies a set of simple opera-

ticns on tabular structures, which can be shown to be of equivalent power to

the first order predicate calculus. A SECUEL user is presented with a consis-

tent set of keyword English templates which reflect how people use tables to

obtain information. Moreover, the SEQUEL user is able to conpose these basic

templates in a structured manner in order to form more complex queries.

SEQUEL is intended as a data base sublanguage for both the professional pro-

grammer and the more infrequent data base user.

Ccmputing Reviews Categories : 3.5, 3.7, 4.2

~ey Words and Phrases: Query Languages

Data Base Management Systems

Information Retrieval

Data Manipulation Languages

249

SEQUEL

INTRODUCTION

As ccnputer systems become more advanced we see a gradual evolution

from pDocedural to declarative problem specification. There are two major

reasons for this evolution. First, a means must be found to lower software

costs among professional programmers. The costs of program creation, main-

tenance, and modification have been rising very rapidly. The concepts of

struct~ired programming (1,2) have been introduced in order to sinplify pro-

gramming and reduce the cost of software. Secondly, there is an increasing

need to bring the non-professional user into effective CuL,t~nication with

a formatted data base. Mudq of the success of the cc~puter industry depends

• on developing a class of users other than trained cc~puter specialists.

The work on the Structu~d English Query Language (SEQUEL), presented

in this paper, is consistent with the trend to declarative problem speci-

fication. It attempts to identify the basic functions that are required by

data base users and to develop a simple and consistent set of rules for

applying these functions to data. These rules are intended to simplify pro-

gramming for the professional and to make data base interaction available to

a new class of users.

A brief discussion of this new class of users is in order here. There

are sane users whose interaction with a ccnlouter is so infrequent or unstruc-

tured that the user is unwilling to learn a query language. For these users,

natural language or menu selection (3,4) seem to be the most viable alter-

natives. However, there is also a large class of users who, while they are

not computer specialists, would be willing to learn to interact with a com-

puter in a reasonably high-level, non-procedural query language. Examples

of such users are accountants, engineers, architects, and urban planners.

It is for this class of users that SEQUEL is intended. For this reason,

SEQUEL emphasizes simple data struct~es and operations.

In a series of papers, E. F. Codd (5-9) has introduced the relational

nDdel of data, which appears to be the simplest possible general-purpose data

structure, and which provides a maxinun degree of data independence. In this

paper we deal only with normalized relations,'which can be viewed as tables

of n columns and a varying number of rows, as illustrated in Figure i.

~4P i NAME SAL MGR DEPT.

I ~4ITH i0000 JC~ES TOY

JONES 12000 ANDERSON FURNI~JRE

i LEE i0000 THCMAS APPLIANCES

Figure i.

Relation describing enployees.

In addition to introducing the relational data structure, Codd has de-

fined a language (9) which allows for the accessing or referencing of data

250

S~EL

in relational format. This language and similar ones (COLARD (i0), RIL (ii))

are based on the first-order predicate calculus. Queries in these languages

typically require:

I. ~he user to define extra variables which have as values rows or portions

of rows of a relation, and

2. The user to state the query using Boolean expressions and universal and

existential quantifiers.

Knuth (12) has shown that the majority of statements in FORTRAN are

rather simple. We believe this is also true of queries to a data base. Pre-

viously, we have presented a data sublanguage called SQUARE (13, 14), which

provides a simple and straightforward mechanism for referencing data in tables.

SQUARE enables the user to describe data selection in terms of set-oriented

table look-ups rather than in a row-at-a-time fashion. This makes possible

the elimination of quantifiers and the elimination of explicit linking terms

used to correlate information frcmn several tables. Therefore, the S~3ARE

user does not need the r~athematical scphistication of the predicate calculus

to make relatively simple references to tables. However, it has been shown

(14) that the SQUARE language is complete, i.e., any query e~qoressible in

the predicate calculus is expressible in SQUARE.

In this paper we attempt to sunnarize the important points of the SQUARE

work and to report on subsequent work to develop a notation more familiar to

tmtrained users than the concise mathematical notation of SQUARE. In devel-

oping this new syntax we have attenloted to keep in mind the notions of top-

down structured programming, the need for a linear notation, and the

need.

for

readable prograns that are easy to maintain and modify. The resulting syntax

can best be described as a block-structured ~glish keyword syntax.

S~MARY C~ SCUARE

In this section, the major features of the SQUARE query language will be

reviewed by a series of examples. A more precise definition of these features

can be found elsewhere (13). In the following sections, the query facilities

of SEQUEL will be introduced and applied to the same set of examples, among

others.

All exmqples of this and later sections are drawn frcm a data base des-

cribing the operation of a department store, and consisting of five tables:

~4P (NAME, DEPT, MGR, SAL, CEMM)

SALES (DEPT, ITS4, VOL)

SUPPLY (SjPpr7~, ITS4, VOL)

IEC (DEPT, FiOOR)

CLass (zn~, TYPE)

25]

of 16

免费下载

文档被以下合辑收录

精品研究报告/论文推荐（共44篇）

精选高品质研究报告和具有里程碑意义的论文供大家参考、学习，持续更新……

文档被以下合辑收录

相关文档

评论