Cyc
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Cyc is an artificial intelligence project which attempts to assemble a comprehensive ontology and database of everyday common-sense knowledge, with the goal of enabling AI applications to perform human-like reasoning.
The project was started in 1984 by Doug Lenat as part of Microelectronics and Computer Technology Corporation. The name "Cyc" (from "encyclopedia", pronounced like psych) is a registered trademark owned by Cycorp, Inc. in Austin, Texas, a company run by Lenat and devoted to the development of Cyc. The original knowledge base is proprietary, but a smaller version of the knowledge base was released as OpenCyc under an open source license. More recently, ResearchCyc (an almost complete version of Cyc) has been made available to AI researchers under a research-purposes license.
Typical pieces of knowledge represented in the database are "Every tree is a plant" and "Plants die eventually". When asked whether trees die, the inference engine can draw the obvious conclusion and answers the question correctly. The Knowledge Base (KB) contains over a million human-defined assertions, rules or common sense ideas. These are formulated in the language CycL, which is based on predicate calculus and has a syntax similar to that of the Lisp programming language. CycL users pun that they are "cyclists".
Much of the current work on the Cyc project continues to be knowledge engineering, representing facts about the world by hand, and implementing efficient inference mechanisms on that knowledge. Increasingly, however, work at Cycorp involves giving the Cyc system the ability to communicate with end users in natural language, and to assist with the knowledge formation process via machine learning.
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Description of the database, terminology
The concept names in Cyc are known as constants. Constants start with "#$" and are case-sensitive. There are constants for:
- Individual items known as individuals, such as #$BillClinton or #$France.
- Collections, such as #$Tree-ThePlant (containing all trees) or #$EquivalenceRelation (containing all equivalence relations). A member of a collection is called an instance of that collection.
- Truth Functions which can be applied to one or more other concepts and return either true or false. For example #$siblings is the sibling relationship, true if the two arguments are siblings. By convention, truth function constants start with a lower-case letter. Truth functions may be broken down into logical connectives (such as #$and, #$or, #$not, #$implies), quantifiers (#$forAll, #$thereExists, etc.) and predicates.
- Functions, which produce new terms from given ones. For example, #$FruitFn, when provided with an argument describing a type (or collection) of plants, will return the collection of its fruits. By convention, function constants start with an upper-case letter and end with the string "Fn".
The most important predicates are #$isa and #$genls. The first one describes that one item is an instance of some collection, the second one that one collection is a subcollection of another one. Facts about concepts are asserted using certain CycL sentences. Predicates are written before their arguments, in parentheses:
(#$isa #$BillClinton #$UnitedStatesPresident)
"Bill Clinton belongs to the collection of U.S. presidents" and
(#$genls #$Tree-ThePlant #$Plant)
"All trees are plants".
(#$capitalCity #$France #$Paris)
"Paris is the capital of France."
Sentences can also contain variables, strings starting with "?". One important rule asserted about the #$isa predicate reads
(#$implies
(#$and
(#$isa ?OBJ ?SUBSET)
(#$genls ?SUBSET ?SUPERSET))
(#$isa ?OBJ ?SUPERSET))
with the interpretation "if OBJ is an instance of the collection SUBSET and SUBSET is a subcollection of SUPERSET, then OBJ is an instance of the collection SUPERSET". Another typical example is
(#$relationAllExists #$biologicalMother #$ChordataPhylum #$FemaleAnimal)
which means that for every instance of the collection #$ChordataPhylum (i.e. for every chordate), there exists a female animal (instance of #$FemaleAnimal) which is its mother (described by the predicate #$biologicalMother).
The knowledge base is divided into microtheories (Mt), collections of concepts and facts typically pertaining to one particular realm of knowledge. Unlike the knowledge base as a whole, each microtheory is required to be free from contradictions. Each microtheory has a name which is a regular constant; microtheory constants contain the string "Mt" by convention. An example is #$MathMt, the microtheory containing mathematical knowledge. The microtheories can inherit from each other and are organized in a hierarchy: one specialization of #$MathMt is #$GeometryGMt, the microtheory about geometry.
OpenCyc
The latest version of OpenCyc, 0.9, was released in February 2005. The knowledge base contains 47,000 concepts and 306,000 facts and can be browsed on the OpenCyc website. The first version of OpenCyc was released in May 2001 and contained only 6,000 concepts and 60,000 facts. The knowledge base is released under the LGPL. The CycL and SubL interpreter (the program that allows you to browse and edit the database as well as to draw inferences) is released free of charge, but only as a binary, without source code. That is, it is freeware, but not free software or open source software. It is available for GNU/Linux and for Windows.
ResearchCyc
Also in February 2005, Cycorp released ResearchCyc 1.0, a gratis (but not free or open source) version of Cyc aimed at the research community. ResearchCyc was in beta stage of development during all of 2004. ResearchCyc is 3 times larger than OpenCyc and includes a large lexicon, English parsing and generation tools, and Java based interfaces for knowledge editing and querying.
Criticisms of the Cyc Project
The Cyc project has been described as "one of the most controversial endeavours of the artificial intelligence history" (ISBN 0-201-87736-8, page 275 section 3.44), so it has inevitably garnered its share of criticism. These include:
- The complexity of the system - arguably necessitated by its encyclopædic ambitions - and the consequent difficulty in adding to the system by hand;
- Scaleability problems from widespread reification, especially as constants;
- Unsatisfactory treatment of the concept of substance and the related distinction between intrinsic and extrinsic properties;
- The lack of any meaningful benchmark or comparison for the efficiency of Cyc's inference engine; and
- The current incompleteness of the system in both breadth and depth and the related difficulty in measuring its completeness.
These issues have been debated in various fora since the inception of the project; Doug Lenat and others have published many arguments in its defence.
See also
External links
- Cyc.com homepage (http://www.cyc.com/)
- opencyc.org - several tutorials (http://www.opencyc.org/)
- research.cyc.com
- Servers that allow public browsing of the OpenCyc knowledge base (http://www.opencyc.org/public_servers)
- OpenCyc C API (http://www.ime.usp.br/~fr/opencyc/)
- Whatever happened to machines that think? 23 April 2005, New Scientist (http://www.newscientist.com/article.ns?id=mg18624961.700)de:Cyc