Cyc

Cyc is a large general ontology.

The main Cyc ontology is commercial, but there is a research license, and no longer maintained OpenCyc. OpenCyc 4.0 can be downloaded on GitHub.

Design

Cyc is divided in modules called microtheories. A microtheory contains assertions (same as axioms in SUMO#).

Assertions within a microtheory need to be consistent with each other, but they can be inconsistent with other microtheories.

For instance, to run a query about whether the planet Earth is able to run a marathon, one has to choose microtheories UniverseDataMt and SportsMt.

Mt : (MtUnionFn UniverseDataMt SportsMt)
EL Query :
(not
  (behaviorCapable PlanetEarth Marathon doneBy))

CycL

Quotes from Panton et al. (2006)

Cyc is written in a language called CycL.

Based on first-order predicate logic

[CycL] is essentially an augmented version of first-order predicate calculus (FOPC). All of the FOPC connectives, such as and, or, and implies are present, as are the quantifiers. One crucial extension was the ability to handle default reasoning; aside from intrinsically definitional information (e.g. “All dogs are mammals”), there are few general statements one can make about the world that cannot have exceptions [, such as] “Dogs have four legs”.

5 truth values

CycL contains five possible truth values: monotonically false, default false, unknown, default true, and monotonically true.

Default logic

Default assertions can be overridden by new knowledge, whether it comes from a person using Cyc or is derived by Cyc’s own inference engine. Instead of using only a single support or line of reasoning to determine if an assertion is true or false, Cyc’s inference engine uses argumentation. This is the process of weighing various arguments, pro and con, to arrive at a truth value for the assertion.

Differences between Cyc and SUMO

Cyc has been around since 1984, and has inspired other ontologies and knowledge bases. SUMO# (released in 2000) is very similar to Cyc. Since there is already a long zettel about SUMO#, I’ll just list some things in which Cyc is different.

Modules and consistency

Cyc is subdivided in microtheories. SUMO is also modular, with an upper ontology, mid-level ontology and domain ontologies. But Cyc doesn’t require all microtheories to be consistent with each other, whereas the whole SUMO is consistent.

For example, a microtheory could describe a fictional world, and that wouldn’t be consistent with others that describe the real world.

Syntax

Prefixes

Cyc prefixes everything with #$. I seriously don’t understand why. It seems to be literally everything. (source):

CYC® constants are referred to with the prefix #$ (read “hash-dollar”). These characters are sometimes omitted in documents describing CycL, and they may be omitted by certain interface tools. But in these CYC® Documentation pages, the policy will be to use the “#$" prefix when referring to CYC® constants.

Arity of functions and predicates

In SUMO, the arity of a function or predicate is expressed by it being an instance of a class, e.g. (instance homeAddress BinaryPredicate).

Cyc has also the same classes {Unary,Binary,…}{Predicate,Fn}. In addition, functions and predicates use a predicate arity to express arity, e.g. (#$arity #$spouse 2)

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