moved from Rulesystem_Arrangement_Framework
This page was initiated by the rule system classification breakout session at the First F2F. See RifRafKickoffScribeNotes. Thanks to PascalHitzler for scribing.
Suggested discriminators for a rule systems ontology
(updated by ChrisWelty, 1/31/06)
FOL vs. other semantics: several languages & systems use non first-order semantics for evaluating rule bodies and heads, examples of these non first-order extensions are:
open (FO) vs. closed vs. hybrid: closed world systems take as false any ground assertion that is not known to be true. Some systems allow for specific closure axioms to be stated about parts of or the entire KB.
monotonic (FO) vs. non-monotonic: non-monotonic systems allow for retraction of existing assertions. In some cases, this includes ground assertions assumed false in a closed world.
forward chaining/backward chaining/hybrid: Generally these are control strategies for performing rule-based inference, however there are subtle semantic consequences to each when combined with other non-FO extensions.
procedural vs. declarative: Rules are generally declarative, I assume what was meant here is the availability (or not) in a rule of procedures (expressed in some programming language) that perform computations (such as doing arithmetic) that are difficult or impossible to express in logic
decidability: Whether or not there are inference procedures for the language that will terminate in all cases.
complexity: The complexity class of the inference procedures. Generally this is the worst-case complexity, however most algorithms can be optimized for certain cases. Rule systems can be classified by their complexity classes.
modality: The standard modalities are alethic (possible/necessary), doxastic (belief), deontic (obligation), and temporal (time). There are potentially many others as, generally speaking, modalities are expressed as quantifiers over possible worlds. Some rulesystems may provide modal operators.
intentionality: Intentionality is generally understood to be "aboutness", that is the relation between a mental object and something in the world the mental object denotes. If we take rules to be expressions of mental objects, I presume what is meant here is something along the lines of documentation, that better conveys the intent behind the formal expression of the rule.