XML DECLARATIVE DESCRIPTION WITH FIRST‐ORDER LOGICAL CONSTRAINTS

The expressive power of XML Declarative Description (XDD), a unified XML‐based representation language for the Knowledge Grid, is enhanced by a well‐defined mechanism for modeling arbitrary XML first‐order logical constraints (FLCs)—a special kind of constraints comprising XML expressions and logical symbols. The resulting knowledge representation can uniformly express explicit and implicit information, ontologies, axioms as well as integrity, structural and FLCs. It facilitates direct use of ordinary XML elements as its basic language component and semantic units, and formally defines XML clauses for modeling advanced complex statements. It achieves sound, efficient, and flexible computation or inference by means of the Equivalent Transformation (ET) paradigm—a new computational model based on semantic preserving transformations. Basic ET computational rules for reasoning with XDD descriptions with FLCs are also presented. Due to its well‐founded mechanism and expressiveness, employment of the proposed representation and computation framework to model a knowledge grid and its services not only enables direct representation of knowledge bases described by such emerging Semantic Web ontology languages as RDF(S) and OWL, but also offers additional descriptive facilities by allowing expression of and reasoning with rules, relationships, and constraints. Moreover, in order to provide machine‐interpretable descriptions of knowledge grid services, standard service description languages, e.g., WSDL, UDDI, OWL‐S and WSMO are employed and extended with facilities to define additional service relationships, constraints, and composition rules.