A posting from Mike Dean (Chair, Joint US/EU ad hoc Agent Markup Language Committee) announces the release of a new DAML+OIL 'semantic [ontology] markup language' specification which includes support for XML Schema Part 2: Datatypes and provides enhanced documentation. The DARPA Agent Markup Language (DAML) "is being developed as an extension to XML and the Resource Description Framework (RDF). The latest release of the language (DAML+OIL) provides a rich set of constructs with which to create ontologies and to markup information so that it is machine readable and understandable." The reference description document characterizes DAML+OIL as "a semantic markup language for Web resources. It builds on earlier W3C standards such as RDF and RDF Schema, and extends these languages with richer modelling primitives. DAML+OIL provides modelling primitives commonly found in frame-based languages. The language has a clean and well defined semantics. A DAML+OIL knowledge base is a collection of RDF triples. DAML+OIL prescribes a specific meaning for triples that use the DAML+OIL vocabulary. The model-theoretic semantics specifies exactly which triples are assigned a specific meaning, and what this meaning is. DAML+OIL only provides a semantic interpretation for those parts of an RDF graph that instantiate the schema defined in daml+oil.daml. Any additional RDF statements, resulting in additional RDF triples are perfectly allowed, but DAML+OIL is silent on the semantic consequences (or lack thereof) of such additional triples." The new '(March 2001)' version of DAML+OIL support documents include the revised language specification, a revised example ontology, the W3C "XSD" datatype definitions set used in the above example, an annotated version of the example ontology, systematic reference description of all the language elements, an explanation of the changes from DAML+OIL (December 2000), revised Model-Theoretic Semantics, and a revised Axiomatic Semantics.

On the datatypes extension: The idea behind DAML+OIL (March 2001) is to extend DAML+OIL (December 2000) with arbitrary datatypes from the XML Schema type system (http://www.w3.org/TR/xmlschema-2/#typesystem), while still retaining the desirable properties of the ontology language, in particular its (relative) simplicity and its well defined semantics. This is achieved by maintaining a clear separation between instances of "object" classes (those defined using our ontology language) and instances of datatypes (defined using the XML Schema type system). In particular, it is assumed that the domain of interpretation of object classes is disjoint from the domain of interpretation of datatypes, so that an instance of an object class (e.g., Leo the Lion) can never have the same interpretation as a value of a datatype (e.g., the integer 5), and that the set of object properties (which map individuals to individuals) is disjoint from the set of datatype properties (which map individuals to datatype values)... the disjointness of the datatype and object domains means that no object can ever be an instance of both an object class and a datatype. However, instances of an object class can be associated with instances of datatypes (data values) via datatype properties. For example, Leo the Lion may be associated with the integer value 5 via the age property. Moreover, we have extend the language so that we can constrain the cardinality and range of datatype properties (both globally and locally) with datatypes. This allows us, for example, to assert that all Animals are associated with a nonNegativeInteger via the age property. The proposal is to add new classes "daml:Class" and "daml:Datatype"; instances of the former are object classes while instances of the latter are datatypes. Similarly, we have the classes "daml:ObjectProperty" and "DatatypeProperty", instances of which are object and datatype properties respectively...