clips(1) an expert system programming language


clips [ file.clp ]


CLIPS is a productive development and delivery expert system tool which provides a complete environment for the construction of rule and/or object based expert systems. CLIPS is being used by numerous users throughout the public and private community including: all NASA sites and branches of the military, numerous federal bureaus, government contractors, universities, and many companies. The key features of CLIPS are:

Knowledge Representation
CLIPS provides a cohesive tool for handling a wide variety of knowledge with support for three different programming paradigms: rule-based, object-oriented and procedural. Rule-based programming allows knowledge to be represented as heuristics, or "rules of thumb," which specify a set of actions to be performed for a given situation. Object-oriented programming allows complex systems to be modeled as modular components (which can be easily reused to model other systems or to create new components). The procedural programming capabilities provided by CLIPS are similar to capabilities found in languages such as C, Pascal, Ada, and LISP.

CLIPS is written in C for portability and speed and has been installed on many different computers without code changes. Computers on which CLIPS has been tested include an IBM PC running DOS and Windows 95 and a Macintosh running MacOS and Mach. CLIPS can be ported to any system which has an ANSI compliant C compiler. CLIPS comes with all source code which can be modified or tailored to meet a user's specific needs.

CLIPS can be embedded within procedural code, called as a subroutine, and integrated with languages such as C, FORTRAN and ADA. CLIPS can be easily extended by a user through the use of several well-defined protocols.

Interactive Development
The standard version of CLIPS provides an interactive, text oriented development environment, including debugging aids, on-line help, and an integrated editor. Interfaces providing features such as pulldown menus, integrated editors, and multiple windows have been developed for the Macintosh, Windows 95, and X Window environments.


CLIPS includes a number of features to support the verification and validation of expert systems including support for modular design and partitioning of a knowledge base, static and dynamic constraint checking of slot values and function arguments, and semantic analysis of rule patterns to determine if inconsistencies could prevent a rule from firing or generate an error.

Fully Documented
CLIPS comes with extensive documentation including a Reference Manual and a User's Guide. (provided in the Debian clips-doc package)


The help for the CLIPS interpreter, type in (help) once the interpreter is run it to read it.


CLIPS is old software so bugs are not unheard of.


The origins of the C Language Integrated Production System (CLIPS) date back to 1984 at NASA's Johnson Space Center. At this time, the Artificial Intelligence Section (later the Software Technology Branch, Client/Server Systems Branch, and now the Information Technology Office) had developed over a dozen prototype expert systems applications using state-of-the-art hardware and software. However, despite extensive demonstrations of the potential of expert systems, few of these applications were put into regular use. This failure to provide expert systems technology within NASA's operational computing constraints could largely be traced to the use of LISP as the base language for nearly all expert system software tools at that time. In particular, three problems hindered the use of LISP based expert system tools within NASA: the low availability of LISP on a wide variety of conventional computers, the high cost of state-of-the-art LISP tools and hardware, and the poor integration of LISP with other languages (making embedded applications difficult).

The Artificial Intelligence Section felt that the use of a conventional language, such as C, would eliminate most of these problems, and initially looked to the expert system tool vendors to provide an expert system tool written using a conventional language. Although a number of tool vendors started converting their tools to run in C, the cost of each tool was still very high, most were restricted to a small variety of computers, and the projected availability times were discouraging. To meet all of its needs in a timely and cost effective manner, it became evident that the Artificial Intelligence Section would have to develop its own C based expert system tool.

The prototype version of CLIPS was developed in the spring of 1985 in a little over two months. Particular attention was given to making the tool compatible with expert systems under development at that time by the Artificial Intelligence Section. Thus, the syntax of CLIPS was made to very closely resemble the syntax of a subset of the ART expert system tool developed by Inference Corporation. Although originally modelled from ART, CLIPS was developed entirely without assistance from Inference or access to the ART source code.

The original intent for CLIPS was to gain useful insight and knowledge about the construction of expert system tools and to lay the groundwork for the construction of a replacement tool for the commercial tools currently being used. Version 1.0 demonstrated the feasibility of the project concept. After additional development, it became apparent that CLIPS would be a low cost expert system tool ideal for the purposes of training. Another year of development and internal use went into CLIPS improving its portability, performance, functionality, and supporting documentation. Version 3.0 of CLIPS was made available to groups outside of NASA in the summer of 1986.

Further enhancements transformed CLIPS from a training tool into a tool useful for the development and delivery of expert systems as well. Versions 4.0 and 4.1 of CLIPS, released respectively in the summer and fall of 1987, featured greatly improved performance, external language integration, and delivery capabilities. Version 4.2 of CLIPS, released in the summer of 1988, was a complete rewrite of

CLIPS for code modularity. Also included with this release were an architecture manual providing a detailed description of the CLIPS software architecture and a utility program for aiding in the verification and validation of rule-based programs. Version 4.3 of CLIPS, released in the summer of 1989, added still more functionality.

Originally, the primary representation methodology in CLIPS was a forward chaining rule language based on the Rete algorithm (hence the Production System part of the CLIPS acronym). Version 5.0 of CLIPS, released in the spring of 1991, introduced two new programming paradigms: procedural programming (as found in languages such as C and Ada;) and object-oriented programming (as found in languages such as the Common Lisp Object System and Smalltalk). The object-oriented programming language provided within CLIPS is called the CLIPS Object-Oriented Language (COOL). Version 5.1 of CLIPS, released in the fall of 1991, was primarily a software maintenance upgrade required to support the newly developed and/or enhanced X Window, MS-DOS, and Macintosh interfaces. Version 6.0, released in the Spring of 1993, added fully integrated object/rule pattern matching and support features for rule-based software engineering. Version 6.1, released in the Summer of 1998, added C++ compatibility and functions for profiling performance.

Because of its portability, extensibility, capabilities, and low-cost, CLIPS has received widespread acceptance throughout the government, industry, and academia. The development of CLIPS has helped to improve the ability to deliver expert system technology throughout the public and private sectors for a wide range of applications and diverse computing environments. CLIPS is being used by over 5,000 users throughout the public and private community including: all NASA sites and branches of the military, numerous federal bureaus, government contractors, universities, and many private companies.

CLIPS is now maintained as public domain software by the main program authors who no longer work for NASA.

There have appeared also derivative works from CLIPS like:

The Java Expert System Shell, which provides a CLIPS interpreter for the Java programming language.

A fuzzy extension of CLIPS.

CLIPS A version of CLIPS using backward chains.


As with any large project, CLIPS is the result of the efforts of numerous people. The primary contributors have been: Robert Savely, previous branch chief of the STB and now chief scientist of advanced software technology at JSC, who conceived the project and provided overall direction and support; Chris Culbert, current chief of the Information Technology Office, who managed the project, wrote the original CLIPS Reference Manual, and designed the original version of CRSV; Gary Riley, who designed and developed the rule-based portion of

CLIPS , coauthored the CLIPS Reference Manual and CLIPS Architecture Manual, and developed the Macintosh interface for CLIPS ; Brian Donnell, who designed and developed the CLIPS Object Oriented Language (COOL), coauthored the CLIPS Reference Manual and CLIPS Architecture Manual, and developed the previous MS-DOS interfaces for CLIPS ; Bebe Ly, who was responsible for maintenance and enhancements to CRSV and is now responsible for developing the X Window interface for CLIPS; Chris Ortiz, who developed the Windows 3.1 interface for CLIPS; Dr. Joseph Giarratano of the University of Houston-Clear Lake, who wrote the CLIPS User's Guide; and Frank Lopez, who designed and developed CLIPS version 1.0 and wrote the CLIPS 1.0 User's Guide.

Many other individuals contributed to the design, development, review, and general support of CLIPS, including: Jack Aldridge, Carla Armstrong, Paul Baffes, Ann Baker, Stephen Baudendistel, Les Berke, Tom Blinn, Marlon Boarnet, Dan Bochsler, Bob Brown, Barry Cameron, Tim Cleghorn, Major Paul Condit, Major Steve Cross, Andy Cunningham, Dan Danley, Mark Engelberg, Kirt Fields, Ken Freeman, Kevin Greiner, Ervin Grice, Sharon Hecht, Patti Herrick, Mark Hoffman, Grace Hua, Gordon Johnson, Phillip Johnston, Sam Juliano, Ed Lineberry, Bowen Loftin, Linda Martin, Daniel McCoy, Terry McGregor, Becky McGuire, Scott Meadows, C. J. Melebeck, Paul Mitchell, Steve Mueller, Bill Paseman, Cynthia Rathjen, Eric Raymond, Reza Razavipour, Marsha Renals, Monica Rua, Tim Saito, Gregg Swietek, Eric Taylor, James Villarreal, Lui Wang, Bob Way, Jim Wescott, Charlie Wheeler, and Wes White.


This manpage was made by Javier Fernandez-Sanguino <[email protected]> for Debian GNU/Linux (but may be used by others)