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CLIPS 30th Anniversary

This year is the 30th anniversary of the creation of CLIPS. Its wikipedia entry contains enough factoids to have earned it this banner:

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.

Since I’ve been involved with the software longer than anyone else, I’ll add my recollections on the veracity of each of the sentences in the wikipedia summary starting with the first:

CLIPS is a public domain software tool for building expert systems.

True. The versions of CLIPS developed while I was at NASA were distributed through COSMIC, but the versions I’ve developed after leaving NASA have been released as public domain software.

The name is an acronym for “C Language Integrated Production System.”

True. The I in CLIPS was sometimes erroneously stated to stand for Inference or Intelligent.

The syntax and name was inspired by Charles Forgy’s OPS (“Official Production System,” although there was nothing really official about it).

With regards to syntax, this is completely false. The only inspiration involved in the early syntax of CLIPS was to avoid reinventing the wheel. At the time, we were using ART for developing expert systems, so CLIPS replicated the ART syntax supporting the primary set of features we used. So credit for the core syntax used by CLIPS goes to ART, not OPS.

As for the name, there’s a definite truthiness to CLIPS being inspired by OPS (since both contain Production System in their acronym), but I think this misses the mark on the significance of CLIPS. The real impetus behind CLIPS was having a tool written in a conventional programming language that could be more easily integrated into operational environments. So the “C Language Integrated” portion of the acronym is more important than the “Production System” portion. Naming it CLIRL (C Language Integrated Rule Language) would have been as appropriately descriptive as CLIPS, but just wouldn’t roll off the tongue as easily. I don’t recall being involved in any discussions about the name, however, so the only person who can definitively answer questions about its inspiration is Robert Savely, my boss at NASA who conceived the project. Next time I see him, I’ll have to ask how he decided on the name.

Oddly, the most important legacy handed down to CLIPS from the OPS languages developed by Dr. Forgy, the Rete algorithm, is not even mentioned in the article.

The first versions of CLIPS were developed starting in 1985 at NASA-Johnson Space Center (as an alternative for existing system ART*Inference) until the mid-1990s when the development group's responsibilities ceased to focus on expert system technology.

Mostly true. The first version of CLIPS was developed in Spring of 1985 by Frank Lopez, but it wasn’t originally developed as an alternative to ART. Initially, it was developed to gain insight into the development of rule-based languages. After additional development it became apparent that CLIPS could be used as a training tool, and then later as an alternative to languages such as ART. Development on CLIPS at NASA did end in the mid-1990s, which is one of the reasons I ended up leaving NASA in 1996.

The original name of the project was NASA’s AI Language (NAIL).

Possibly or somewhat true, but also an example of why specific words need to be chosen to convey precise meaning. The source for this statement may be Frank’s website that uses the words “first proposed name” rather than “original name.” I have no doubt that NAIL was proposed as a name for the project as Frank states, but to be the original name of the project as the wikipedia article claims implies that at some point NAIL was selected, but then subsequently changed to CLIPS. Yes, this is splitting hairs, but I’m not the one who flagged the article for lack of citation.

On a different note, this is an odd bit of information to include as part of a brief description of a programming language.

CLIPS is probably the most widely used expert system tool.

Fifteen to twenty-five years ago I think you could make a reasonable argument for this claim, but today I think you could only claim that CLIPS is widely used.

On SourceForge CLIPS had around 30,000 downloads in 2014 (which could roughly be split to around half for executables and half for source code, documentation, and example programs). That places it in the top ten downloads on SourceForge for artificial intelligence software.

On the Stack Overflow question forum, there are 165 questions with the clips tags, 101 with the jess tag, and 80 with the jrules tag. On the other hand, the drools tag is associated with 1,546 questions. That makes a pretty strong argument that Drools is now more widely used than CLIPS.

CLIPS incorporates a complete object-oriented language (hence the acronym COOL) for writing expert systems.

True, although this sentence might lead one to believe that the acronym COOL stands for Complete Object-Oriented Language rather than CLIPS Object-Oriented Language.

CLIPS itself is written in C, extensions can be written in C, and CLIPS can be called from C.

True. CLIPS has also been integrated with many other languages including C++, .NET, Java, Perl, and Python.

Its user interface closely resembles that of the programming language Lisp.

True, but it could be more precisely stated that the CLIPS user interface is a read-eval-print loop.

COOL combines the programming paradigms of procedural, object oriented and logical (theorem proving) languages.

False. This sentence ignores the terminology used in the CLIPS Reference Manuals. I suppose this would be OK if you were comparing two or more languages that used different terminology for similar features, but that’s not the case here. CLIPS supports three programming paradigms: rule-based, object-oriented, and procedural. The documentation never refers to the procedural paradigm as being part of COOL and there’s no mention at all of a logical (theorem proving) paradigm.

A language with a similar approach is Planner, which also combines traits of logical languages like Prolog with the capabilities of procedural and OO-languages like C++.

Huh? How is Planner a good example of a language that takes a similar approach? Jess, JRules, and Drools are far better examples since they combine a forward chaining rule engine (much more similar to CLIPS than Prolog) with an object-oriented language.

And that’s it. No more sentences left for a thumbs up or thumbs down.

Yosemite Olaf