| Abstract | XML is a description format for encoding and exchange of structured data and documents
on the Web, which lacks a computation mechanism as well as expressiveness by not
allowing specification of domain knowledge, axioms, conditional relationships and con-
straints. Existing approaches to the removal of these limitations demand certain extensions
as well as integration of additional formalisms, which not only complicate their syntax and
semantics, but also their understanding.
With the aim of removal of these defects, XML Declarative Description (XDD)—an
expressive knowledge representation with precise, well-defined semantics and efficient
computation mechanisrn—employs XML’s nested tree structure as its underlying data
structure and Declarative Description theory as a framework to enhance its expressive
power. It enables direct representation of data items, encoded in XML-based application
markup languages, and extends their expressiveness by facilitation of simple means for
succinct and uniform expression of implicit information, integrity constraints, conditional
relationships and axioms. In addition, it allows their semantics to be determined directly,
and also provides efficient computation by means of Equivalent Transformation (ET).
Thus, with its simplicity, yet flexibility, generality and expressiveness, XDD embraces
those existing approaches and can serve as their foundation for representation and compu-
tation.
XDD can be applied to diverse areas including XML document manipulation, database
management, query formulation and evaluation as well as Semantic Web modeling and
programming.
Application of XDD to XML (document) database modeling allows the three compo-
nents of an XML database—an extensional database, an intensional database, and struc-
tural and integrity c0nstrain!s—to be formalized simply as an XDD description; its
semantics is a set of XML elements which are explicitly described by the extensional data-
base or implicitly derived from the database, based on the defined intensional database,
and which satisfy all the specified constraints. Thus, selective and complex queries,
regarding information satisfying certain criteria and possibly implicit in the database, for-
mulated as XDD descriptions, become expressible and computable. Moreover, since a
DTD or an XML Schema can be represented by a corresponding XDD description, it also
yields an algorithm for validation of document conformance‘ XDD thereby serves as an
effective and well-founded )G\/IL database framework with succinct representational and
operational uniformity, reasoning capabilities and deductive query supports.
The present XDD approach to modeling of Semantic Web resources and applications
demonstrates that every component of Semantic Web resources—constraints, ontologies
and contents—and of Semantic Web applications—applicati0n data, application rules and
queries/requests—can be represented uniformly as an XDD description. |