In this paper, we present a data and an execution model that allow for efficient storage and retrieval of XML documents in a relational database. The data model is strictly based on the notion of binary associations: by decomposing XML documents into small, flexible and semantically homogeneous units we are able to exploit the performance potential of vertical fragmentation. Moreover, our approach provides clear and intuitive semantics, which facilitates the definition of a declarative query algebra. Our experimental results with large collections of XML documents demonstrate the effectiveness of the techniques proposed.

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Benchmarks belong to the very standard repertory of tools deployed in database development. Assessing the capabilities of a system, analyzing actual and potential bottlenecks, and, naturally, comparing the pros and cons of different systems architectures have become indispensable tasks as databases management systems grow in complexity and capacity. In the course of the development of XML databases the need for a benchmark framework has become more and more evident: a great many different ways to store XML data have been suggested in the past, each with its genuine advantages, disadvantages and consequences that propagate through the layers of a complex database system and need to be carefully considered. The different storage schemes render the query characteristics of the data variably different. However, no conclusive methodology for assessing these differences is available to date.In this paper, we outline desiderata for a benchmark for XML databases drawing from our own experience of developing an XML repository, involvement in the definition of the standard query language, and experience with standard benchmarks for relational databases.

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