Bernadette Farias Lósio
Ana Carolina Salgado
ABSTRACT
XML has become the standard format for representing structured and semi-structured data on the Web. To describe the structure and content of XML data, several XML schema languages have been proposed. Although being very useful for validating XML documents, an XML schema is not suitable for tasks requiring knowledge about the semantics of the represented data. For such tasks it is better to use a conceptual schema. This paper presents an extension of the Entity Relationship (ER) model, called X-Entity, for conceptual modeling of XML schemas. We also present the process of converting a schema, defined in the XML Schema language, to an X-Entity schema. The conversion process is based on a set of rules that consider element declarations and type definitions and generates the corresponding conceptual elements. Such representation provides a cleaner description for XML schemas by focusing only on semantically relevant concepts. The X Entity model has been used in the context of a Web data integration system with the goal of providing a concise and semantic description for local schemas defined in XML Schema.
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Digital Library
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Index Terms
- Conceptual modeling of XML schemas
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Reviews
Vladan Jovanovic
A new conceptual modeling notation, X-Entity, is introduced in this paper. X-Entity, an extension of the entity relationship (ER) model, is suitable for representing Extensible Markup Language (XML) schemas. X-Entity model extensions include containment relationships, occurrence constraints for elements and attributes, and choice groups. The paper also presents an interesting algorithm for generating conceptual X-Entity schemas from XML schemas. A data model for an XML schema can be represented using traditional notations, such as ER, integration definition for function modeling (IDEF1X), or unified modeling language (UML). Furthermore, those same notations can be used to represent XML schema metamodels, so one might ask what is new here. What the X-Entity model offers is an independent representation of XML schema instances in a stylized manner, using an enriched conceptual version of the ER model. This is both an advantage and a drawback for X-Entity as a technology. It provides semantically richer descriptions than those produced using general purpose modeling notations, but to achieve this, users have to acquire yet another formalism. Among the apparent weaknesses of this formalism is a lack of direct support for hierarchy modeling, which is one of the core features of XML. While time will reveal the future of X-Entity, the proponents of this technology have yet to present a compelling case to attract potential users. Online Computing Reviews Service
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