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OPS5

Language type:

L - Rule-based or logical

Description:

OPS5 is a production rule programming language for AI research and building expert systems. The OPS family of rule-based systems culminated with OPS5, which has been widely used for AI instruction and application development.
An OPS5 program consists of a set of production rules. Each rule has a precedent, or set of conditions which govern application of the rule, and an antecedent which define actions to take upon triggering the rule. OPS5 supports both forward-chaining and backward-chaining control models.
Data in the OPS5 model is handled as a set of global state variables and records which can be modified by the rules. Production rules reside in "production memory", while data values reside in "working memory". Primitive data types are numbers and symbols (symbols also serve as strings). OPS5 is weakly typed, like Lisp: variables are not declared to have a particular type, but can hold any type of data placed in them. Working memory contains objects that bear attributes: these attributes can hold primitive data values, vectors, or references to other objects.
OPS5 has been largely superseded by newer expert-system shells (such as CLIPS) and rule-based languages (such as OPS83).
The first version of OPS5 was coded in Lisp. Later versions were written in C for speed. Both commercial and free academic editions of OPS5 existed during the 1980s. Free implementations of OPS5 (C and Lisp) are supposedly available. Documentation on the language is not easily available on the net.

Origin:

Charles Forgy et al, 1977.

See Also:

Lisp    Prolog   

Remarks:

The syntax and semantics of OPS5 are highly specialized for the task of writing rule-based systems that model real-world situations. The division of the programming model into "production" and "working" memory was based on cognitive psychology frameworks of human thought processes: long-term memory is equated to domain knowledge and corresponds to production rules, and short-term memory is equated to facts about the situation at hand and corresponds to objects in working memory.
In any OPS5 program, the toughest part is ensuring that the right domain-specific rule is applied to the working memory at the right moment. OPS5 supports various grouping and priority schemes to allow the programmer to guide the execution of rules; applying these facilities can be tricky.

Date:

Last updated 12/22/97

Sample code:

; An OPS5 program that implements a model of
; rock climbers, from exercise solutions of 
; "Expert Systems Programming in OPS5"
(literalize rock-climber
    age       ; young or old
    style     ; timid or bold
)

(p old-not-bold
    (rock-climber ^age old ^style <> bold)
--->
    (write (crlf) that is plausible))

(p bold-not-old
    (rock-climber ^age <> old ^style bold)
--->
    (write (crlf) that is quite possible))

(p error::old-and-bold
    (rock-climber ^age old ^style bold)
--->
    (write (crlf) There are no old, bold rock climbers))

(make rock-climber ^age young ^style bold)

Descriptions in this dictionary are ©1997-99 Neal Ziring. Some examples copyright of their respective authors. Some technologies and languages are trademarked. Permission to copy descriptions is granted as long as authorship credit is preserved.

Comments on this dictionary, corrections and suggestions, are all welcome. Please use email, the address is ziring@home.com