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In the proposed data model for XML databases, an XML element is directly represented as a ground (variable-free) XML expression--a generalization of an XML element by incorporation of variables for representation of implicit information and enhancement of its expressive power--while a collection of XML documents as a set of ground expressions, each describing an XML element in the documents. Relationships among elements in the collection as well as integrity constraints are formalized as XML clauses. An XML database, consisting of: (i) a document collection (or an extensional database), (ii) a set of relationships (or an intensional database) and (iii) a set of integrity constraints, is therefore modeled as an XML declarative description comprising a set of ground XML expressions and XML clauses. Its semantics is a set of ground XML expressions, which are explicitly described by the extensional database or implicitly derived from the intensional database and satisfy all the specified set of constraints.

This appendix gives a brief overview of the XML language and the reasons why it has been chosen as a file exchange format for IEC 61499 library elements, for example, for exchanging function block definitions between engineering support systems and other IEC 61499 compliant applications.

In various application, it may be necessary to obtain XML representation from data maintained in relational databases. This paper presents a language called XML/SQL which is aimed at the specification of XML documents extracted from the results of relational queries. XML/SQL allows the creation of documents of arbitrary structure regardless of the structure of the relational data source. Further, XML/SQL is a declarative language, i.e., no procedural specification of the result is required.

Summary: An XML document type definition (DTD) is provided for the description of taxonomic relationships between organisms. Two XSL stylesheets for the graphical presentation of simple taxonomic trees are also provided. Availability: The DTD and stylesheets along with sample files are available at http://www.albany.edu/~gilmr/pubxml/. Contact: gilmr@cnsvax.albany.edu

XML is just becoming a standard for document processing and interchange on the Internet. In this context, XML's DTD structuring mechanism is especially important. This paper addresses, among others, the problem of integration of several DTDs by introducing a grammar based model for XML based on so called xtrees and xschemes. Although it can be shown that we can always find a DTD describing the intersection of the languages defined by two arbitrarily given DTDs, the same is not true for the union. This result shows that pure DTDs are not sufficient for schema integration. The paper presents a solution to this problem by introducing and investigating a generalized model based on so called s-xschemes. Using these s-xschemes we can obtain additional information about XML documents belonging to certain classes, thus enabling computation and transformation of information more specifically.

XML data are expected to be widely used in Web information systems and EC/EDI applications. Such applications usually use a large number of XML data. First, we must allow users to retrieve only necessary portions of XML data by specifying search conditions to flexibly describe such applications. Second, we must allow users to combine XML data from different sources. To this end, we will provide a query language for XML data tentatively called XQL. We have designed XQL, keeping in mind its continuity with database standards such as SQL and OQL although we don't stick to its strict conformity. In this paper, we describe the requirements for a query language for XML data and explain the functionality of XQL including XML version of database operators such as select, joint, sort, grouping, union, and view definition. We make brief comments on the implementation and semantics.

The problem that XML formally governs syntax only but not semantics has been recognized as a serious barrier for XML-Based data integration and the extension of current Web to the semantic Web. To address this problem, the XML Semantics Definition Language (XSDL) is proposed to explicitly express the XML author's intended meaning and a model-theoretic semantics for XML. In this way, the XML becomes a sub-language of RDF (resource description framework) in expressivity and the XML data can be semantics-preserving transformed to the RDF data. The semantic validity and entailment problem of XML documents are further provided and they are reduced to the knowledge base unsatisfiability problem in description logic language SHOIN�∆