On Defining Keys for XML

Keys are an important part of any data model. In relational model, keys are well studied and are widely used. In recent years, XML has emerged as an widely used data representation and storage format in the world wide Web. The data centric approach of XML has necessitated the definition of integrity constraints for XML. XML key is regarded as one of those integrity constraints. In this paper, we define XML keys, specifically for the purpose of XML data transformation and integration with integrity constraints. In the proposal, we show how XML keys are defined on the XML document type definition (DTD) and are satisfied by the XML documents. We introduce the novel concept P-tuple (pair-wise tuple) that produces semantically correct tuples in the XML document during key satisfaction. Our definition for XML keys can also be extended to XML relative keys. Finally, we discuss how our proposal for XML keys has some advantages over other previous proposals and standards.