A Normal Form for XML Documents

Marcelo Arenas, Leonid Libkin

Research output: Contribution to journalArticlepeer-review


This article takes a first step towards the design and normalization theory for XML documents. We show that, like relational databases, XML documents may contain redundant information, and may be prone to update anomalies. Furthermore, such problems are caused by certain functional dependencies among paths in the document. Our goal is to find a way of converting an arbitrary DTD into a well-designed one, that avoids these problems. We first introduce the concept of a functional dependency for XML, and define its semantics via a relational representation of XML. We then define an XML normal form, XNF, that avoids update anomalies and redundancies. We study its properties, and show that XNF generalizes BCNF; we also discuss the relationship between XNF and normal forms for nested relations. Finally, we present a lossless algorithm for converting any DTD into one in XNF.
Original languageEnglish
Pages (from-to)195-232
Number of pages38
JournalACM Transactions on Database Systems
Issue number1
Publication statusPublished - Mar 2004


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