|2006-11-11 -||Version 0.91|
This is the specification of Modal RuleML 1.0.
Inspired by previous work on many-dimensional modal logic and multi-modal logic, Modal RuleML was first described in the 'Family' RuleML paper ('Family' RuleML slides), co-evolved with parallel efforts including Semantics of Business Vocabulary and Business Rules, and revised for Modal RuleML 1.0.
Modal RuleML 1.0 uses (modal-)relationship Atoms applying a modal relation
<Rel modal="http://ruleml.org/1.0/vocab/modal/logic#Operator"/>to an optional agent argument and a mandatory embedded proposition
<Atom per="instant" ...> . . . </Atom>(hence the relation is unary or binary, i.e. polyadic). Here, http://ruleml.org/1.0/vocab/modal/logic#Operator is a system of six reserved IRIs representing the modality of a logic (currently, alethic, deontic, epistemic, and doxastic) and an Operator (e.g., for alethic being Necessary or Possible). Moreover, per="instant" indicates the use of the inner atom 'per instantiation', so that free variables inside this embedded proposition can be quantified over from outside the modal relationship. The six logic#Operator pairs introduced are alethic#Necessary, alethic#Possible, deontic#Obligatory, deontic#Permitted, epistemic#Known, and doxastic#Believed. Each can be used polyadically in a unary, 'absolute' fashion, i.e. applied to the embedded proposition only, or in a binary, 'relativized' version, i.e. applied to an agent as well as to the embedded proposition. The modal relationships can be defined both by facts and rules. For example, the absolute "It is known that the material of the moon is rock" in Modal RuleML becomes the following unary epistemic#Known fact:
<Atom> <Rel modal="http://ruleml.org/1.0/vocab/modal/epistemic#Known"/> <Atom per="instant"> <Rel>material</Rel> <Ind>moon</Ind> <Ind>rock</Ind> </Atom> </Atom>This can be relativized to Mary, as in "It is known by Mary that the material of the moon is rock", which in Modal RuleML's polyadic formalization becomes the binary epistemic#Known fact:
<Atom> <Rel modal="http://ruleml.org/1.0/vocab/modal/epistemic#Known"/> <Ind>Mary</Ind> <Atom per="instant"> <Rel>material</Rel> <Ind>moon</Ind> <Ind>rock</Ind> </Atom> </Atom>In English this would of course be normally expressed as "Mary knows that the material of the moon is rock". The advantage of using relativizable modalities such as epistemic#Known polyadically rather than having both a unary and a binary version such as, respectively, epistemic#Known and epistemic#Knows is that it cuts the number of reserved IRIs in half.
Following the same principles, extensions of Modal RuleML 1.0 are expected to introduce further modalities such as for spatio-temporal structures. New modalities can initially be developed at RuleML-external IRIs ending with logic#Operator and on approval by the Modal Logic in RuleML Technical Group become added as RuleML-internal reserved IRIs. Note that the current release does not yet contain temporal logic, because of trade-offs between qualitative and quantitative treatments of time, the many temporal-logic varieties (starting with the pairs of temporal operators for the past and for the future), and ongoing related developments in Reaction RuleML (e.g., CEP RuleML) and LegalRuleML.
A methodology for extending defeasible logic with modality for RuleML is described in the Modal Defeasible Logic paper (Modal Defeasible Logic slides). An extension of the defeasible reasoner DR-DEVICE with a mechanism for expressing modal (e.g., deontic) logic operators is described in the Modal Defeasible Reasoner paper.
Various sample Modal RuleML documents have been prepared and maintained; some exemplify features of Modal RuleML and are useful didactically while others are mostly for testing puposes.
A suite of instructive examples for Modal RuleML has been developed at CombiningModalLogics.ruleml (cf. wiki history).
The schema specification of Version 1.0 has been created at http://ruleml.org/1.0/modal/modal.xsd
Work on this specification has been initially in collaboration with the EU's REWERSE Network of Excellence (modal and reactive logic), ongoing with OMG's SBVR Task Force (alethic and deontic logic), and recently with OASIS' LegalRuleML Technical Committee (deontic and defeasible logic).
Page Version: 2012-09-08
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