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Loops in Decision Tables

IP.com Disclosure Number: IPCOM000079327D
Original Publication Date: 1973-Jun-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 71K

Publishing Venue

IBM

Related People

Sharman, GCH: AUTHOR

Abstract

It has been demonstrated that decision tables may be used to represent structures of tests which frequently appear in computer programs. IBM Technical Disclosure Bulletin, Vol. 14, No. 12, May 1972, pages 3747 and 3748. Here it is shown that loops may also be represented, and that decision tables may form elements of structured programs.

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Loops in Decision Tables

It has been demonstrated that decision tables may be used to represent structures of tests which frequently appear in computer programs. IBM Technical Disclosure Bulletin, Vol. 14, No. 12, May 1972, pages 3747 and 3748. Here it is shown that loops may also be represented, and that decision tables may form elements of structured programs.

The transfer of control out of a decision table may be interpreted in a number of ways. Fig. 1 illustrates a simple interpretation in which the exit from each column of the decision table is out of the table. The scope of the decision table is thus the same as that of a PL/1 DO-group containing a nest of IF statements. This is a structure commonly employed in so-called "structured programs", i.e., it represents a block having one entry and one exit and composed only of simple structures.

This type of decision table may be generalized to represent DO-Loops as well as DO-groups, by the use of a special action statement. This is referred to as the "END" statement. The effect of this statement is to cause control to return to beginning of the decision table on exit from a given column. With this device, conventional count loops and WHILE loops can be represented by decision tables. Examples are given in Figs. 2 and 3.

A major advantage of this notation is that it may be used to represent valid program structures, which cannot be represented by conventional loops in a simple way. These structures are those in...