Algebra and the Formal Semantics of GLASS
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Date
2005-09-13
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Abstract
In database world, it is common to translate a query language into an algebra for the purpose of precisely defining the formal semantics of a query language and doing query optimization later. In this paper, we examine the scenario of graphical XML query languages, focus on their expressive power and present the underlying algebra of our graphical XML query language. Compared with various previous works on XML algebra, our algebra supports not only traditional select, project and join operators but also swap and SQL-like group operators. To achieve the exactness in query representation, we use ORA-SS (Object-Relationship-Attribute model for Semi-Structured data), a semantic rich data model for XML including the information such as Key constraints, Functional dependencies and Relationship types which are lacked in DTD. With examples, we show how our graphical language solves the difficult points in representation and how it is translated into our algebra. Based on the translation, we use the algebra to define the formal semantics of GLASS.