Frequently Asked Questions

  1. What is CLIPS?
  2. Where Can I Get a Copy of CLIPS?
  3. What's New in Version 6.2 of CLIPS?
  4. Can CLIPS Be Redistributed? Are There Any Licensing Fees?
  5. What Forums Are Available For Answering Questions About CLIPS?
  6. Are There Any Sources Describing Applications Built Using CLIPS?
  7. Are There Any Textbooks Using CLIPS?
  8. Are There Any Special Versions of CLIPS?
  9. Can CLIPS be Integrated with C++ Code?
  10. Is a Dynamic Link Library Available for CLIPS?
  11. What are the Origins of CLIPS?
  12. Are There Any Languages Similar to CLIPS?
  13. What are the Future Plans for CLIPS?
  14. Can CLIPS be Used for Real Time Applications?
  15. Are There Any Examples of User Defined Functions Other Than the Ones in the Advanced Programming Guide?
  16. Does a Run-Time Program Generated Using the Constructs-To-C Command Run any Faster Than a Program Loaded Using the Load or Bload Commands?
  17. Is the CLIPS 6.X Architecture Manual Available?
  18. Are Consulting/Training Services Available for CLIPS?
  1. What is CLIPS?

    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. Created in 1985, CLIPS is now widely used throughout the government, industry, and academia. Its key features are:

  2. Where Can I Get a Copy of CLIPS?

    CLIPS executables, documentation, source code, and examples can be downloaded from the Download Page of the CLIPS Project on SourceForge.

  3. What's New in Version 6.2 of CLIPS?
  4. Can CLIPS Be Redistributed? Are There Any Licensing Fees?

    Copies of CLIPS executables, documentation, and source code downloaded from the CLIPS Project on SourceForge are subject to the following license agreement:

    Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY RIGHTS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, OR ANY SPECIAL INDIRECT OR CONSEQUENTIAL DAMAGES, OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

  5. What Forums Are Available For Answering Questions About CLIPS?
  6. Are There Any Sources Describing Applications Built Using CLIPS?

    There are a number of sources describing applications built using CLIPS:

  7. Are There Any Textbooks Using CLIPS?

    Expert Systems: Principles and Programming, 4th Edition, by Giarratano and Riley (ISBN 0-534-38447-1), comes with a CD-ROM containing CLIPS 6.22 executables, source code, and documentation. The first half of the book is theory oriented and the second half covers rule-based, procedural, and object-oriented programming using CLIPS. For more information, contact Course Technology.

    Introduction To Expert Systems, 3rd Edition, by Jackson (ISBN 0-201-87686-8), contains numerous CLIPS examples and exercises throughout the book. For more information, contact Addison Wesley.

    The Engineering of Knowledge-based Systems: Theory and Practice, by Gonzalez and Dankel (ISBN 0132 769 409), comes with an MS-DOS executable of version 5.1 of CLIPS. The use of CLIPS isn't integrated throughout the book, but there is a 25 page appendix that describes the fundamentals of using the CLIPS executable bundled with the book. For more information, contact Prentice Hall.

  8. Are There Any Special Versions of CLIPS?
  9. Can CLIPS be Integrated with C++ Code?

    Yes. Version 6.1 and later can be compiled with either an ANSI C or C++ compiler. However, the CLIPS source code only uses features that are available in both the ANSI C and C++ standards. Since the object extensions of C++ are not part of the ANSI C standard, they are not utilized in the CLIPS source code. CLIPS 6.3 comes with starter projects which demonstrate how to build a C++ library.

    The clipsmm library is a C++ interface to CLIPS.

  10. Is a Dynamic Link Library Available for CLIPS?

    There are several DLLs available for use with CLIPS:

  11. What are the Origins of CLIPS?

    The origins of CLIPS date back to 1984 at NASA's Johnson Space Center. At this time, the Artificial Intelligence Section 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.

    The Artificial Intelligence Section felt that the use of a conventional language, such as C, would eliminate most of these problems. 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 1985. Particular attention was given to making the tool compatible with expert systems under development at that time. 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.

    In the mid 1990s the focus of the Artifical Intelligence Section (now the Software Technology Branch) shifted away from expert system technology. The principle developers subsequently left NASA. CLIPS is now maintained independently from NASA as public domain software by one of the original program authors. The first public domain release of CLIPS, version 6.1 in 1998, removed support for older non-ANSI C Compilers and added support for C++ compilers. Commands to profile the time spent in constructs and user-defined functions were also added. Version 6.2, released in the Spring of 2002, added support for multiple environments into which programs can be loaded and improved Windows XP and MacOS development interfaces.

  12. Are There Any Languages Similar to CLIPS?

    CLIPS is an interesting example of technology transfer between the government and private sectors. Syntactically, CLIPS traces its origins to Inference's ART which traced the origins of its rule-based language to OPS5. Later, CLIPS was used by Inference to develop ART-IM (which later became ARTEnterprise, by The Haley Enterprise to develop Eclipse (which later became HaleyRules), and by Production Systems Technology to develop CLIPS/R2. Other languages, such as Jess, adopted syntax similar to ART and CLIPS. This has created a family of tools that share the same basic syntax for the definition of rules. While the features and capabilities of these tools has diverged sufficiently that porting an application taking full advantage of a tool's complete feature set is non-trivial, it's still possible if one uses a restricted subset of features to write portable programs that will run with few if any simple changes.

  13. What are the Future Plans for CLIPS?

    Version 6.3 will target rule performance, improved integration with other languages (such as C++, .NET, and Java), and examples for common use cases. Version 6.4 will target unicode support.

  14. Can CLIPS be Used for Real Time Applications?

    Yes and no. It depends on what you mean by a real time application.

    If you want guaranteed response time, then the answer is no. Generally speaking, the more robust the pattern matching capabilities of a tool, the more difficult it is to guarantee real time response.

    If you need built-in functionality that allows you reason about events as they occur over time, then the answer is no. Many tools designed for real time applications provide features that allow you (among other things) to schedule rules to be checked at a particular time or on a particular time interval, specify how long data is valid, determine trends in data (such as whether it's increasing or decreasing), and synchronize the execution of tasks. In addition, some tools provide extensive facilities for the "non AI" related aspects of developing a real time application such as the graphical interface, simulation, and data acquisition. It's possible to use CLIPS to reason about events as they occur over time--It's just not a built-in feature. You can, for example, add an additional slot to facts which stores their creation time and then use rules which reason based on the contents of this slot.

    If by real time you mean that the application is able to keep up with the data as it is received, then the answer is maybe. Almost all expert system tools can keep up with a real time system that only requires decisions to be made in minutes/hours/days. Response time tends to become an issue only when large amounts of data are being processed or decisions are required in seconds or fractions of a second.

    CLIPS is based on the Rete pattern matching algorithm. The efficiency of this algorithm is based on the assumption that data changes slowly over time (e.g. a single rule firing affects < 5% of all facts). This assumption would appear to fail miserably for monitoring applications (as well as other applications where rapid data change can occur). If, for example, you have 100 facts representing various sensor values and the sensor values change every second, you have very rapid data changes (assuming you don't have thousands and thousands of facts of other types). It's often possible to comply with the Rete assumption by preprocessing data. For example, if a sensor value changes from 10 to 10.1 and this change is not significant, then it's not necessary to retract the old fact and assert a new fact with the changed sensor value. Another preprocessing approach would be to convert numeric values to symbolic values such as low, nominal, and high and then to retract the old fact and assert a new one only if the symbolic value changed. The major drawback to this approach is that you generally have to write C code to preprocess the data and keep track of pointers to facts so that facts can later be retracted by the preprocessor--Of course if you're dealing with real-time data, you're probably writing some C code anyway.

  15. Are There Any Examples of User Defined Functions Other Than the Ones in the Advanced Programming Guide?

    Virtually all of the system defined functions that come ready to use with CLIPS utilize the same programming interface that you have to use to define your own functions. Look through files in the CLIPS source code such as bmathfun.c, iofun.c, miscfun.c, prdctfun.c, emathfun.c, filecom.c, and multifun.c for examples.

  16. Does a Run-Time Program Generated Using the Constructs-To-C Command Run any Faster Than a Program Loaded Using the Load or Bload Commands?

    A run-time program will not run any faster than a program loaded using the load or bload commands. The constructs-to-c command used to generate a run-time program creates files containing the C data structures that would dynamically be allocated if the load or bload command was used. With the exception of some initialization routines, the constructs-to-c command does not generate any executable code. The primary benefits of creating a run-time program are: applications can be delivered as a single executable file; loading constructs as part of an executable is faster than loading them from an text or binary file; the CLIPS portion of the run-time program is smaller because the code needed to parse constructs can be discarded; and less memory is required to represent your program's constructs since memory for them is statically rather than dynamically allocated.

  17. Is the CLIPS 6.X Architecture Manual Available?

    There are no plans to write a 6.X Architecture Manual. Copies of the CLIPS 5.1 Architecture Manual are still bundled with the CLIPS documentation.

  18. Are Consulting/Training Services Available for CLIPS?

    Inquiries about consulting, training, or other employment opportunities can be sent to gdrworkYYYY@swbell.net or clipsYYYY@swbell.net where YYYY is the current year (for example, 2008).

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Last Update January 25, 2008 Gary Riley