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Tabular Expression of Criteria

IP.com Disclosure Number: IPCOM000062561D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 16K

Publishing Venue

IBM

Related People

Larner, A: AUTHOR

Abstract

In a system in which a user enters truth-functional combinations of criteria, the permissible sequence of application of truth-functional connectives may be constrained by allowing only one such operator to be prefixed (or suffixed) to any criterion in order to avoid syntactical complexity and so increase the usability, or 'friendliness', of the system. A criterion can be taken to comprise two expressions connected by some relational operator, and the truth-functional connectives envisaged are 'NOT', 'AND', and 'OR' (others, such as 'Exclusive OR' might also be considered). Typical relational operators are 'EQ' or '=' for equality, 'LT' or '<' for 'less than'; no restriction is placed on what other operators might be used.

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Tabular Expression of Criteria

In a system in which a user enters truth-functional combinations of criteria, the permissible sequence of application of truth-functional connectives may be constrained by allowing only one such operator to be prefixed (or suffixed) to any criterion in order to avoid syntactical complexity and so increase the usability, or 'friendliness', of the system. A criterion can be taken to comprise two expressions connected by some relational operator, and the truth-functional connectives envisaged are 'NOT', 'AND', and 'OR' (others, such as 'Exclusive OR' might also be considered). Typical relational operators are 'EQ' or '=' for equality, 'LT' or '<' for 'less than'; no restriction is placed on what other operators might be used. The restriction allows each criterion, along with its truth-functional connective, to be written in one line of a table. A collection of such criteria comprises an ordered list of lines, each criterion being a line comprising four elements, in sequence: a truth functional connective (including a 'blank' connective), a left expression, a relational operator, and a right expression. For example : *** height EQ 180 AND weight GT 220

OR age LT 30 As the user of such a rigidly formatted set of criteria is relieved of the necessity to control the application sequence of the connectives (for example, by using parentheses), it is necessary to define rules of sequence, which should themselves: (1) be easy to remember, (2) allow any truth-function of criteria to be expressed, and (3) minimize the amount of data entry by the user, in particular, the number of times a criterion is entered. That such definition of sequence is necessary is shown by the ambiguity of the above example, which might be interpreted in two ways: OEheight EQ 180 and either weight GT 220 or age LT 30 ('OR evaluated before 'AND') OEeither height EQ 180 and weight GT 220 or age LT 30 ('AND' evaluated before 'OR') It is known that either conjunctive normal form (CNF) or alternational normal form (ANF) is sufficient to ensure (2). CNF requires the set of criteria to be a conjunction of alternations of criteria or negations of criteria; ANF requires it to be an alternation of conjunctions. Either of these would require only four possible connectives to be entered in the first column of the tabulation; AND, AND- NOT, OR, and OR-NOT. The use of 'AND-NOT' or 'OR-NOT' is avoided by ensuring that if any relation operator is available, then its negation is also available (for example, inequality as well as equality, 'not less than' as well as 'less than'). The blank connective must be interpreted in some way, and it is both intuitively and theoretically correct to interpret it as conjunction (AND). Thus height EQ 180 weight GT 220 should be understood as height

EQ 180

AND weight GT 220 The theoretical correctness of this depends upon understanding an empty set of criteria to have the

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value TRUE. A single criterion (w...