This paper takes a rst 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 nd a way of converting an arbitrary DTD into a well-designed one, that avoids these problems. We rst introduce the concept of a functional dependency for XML, and de ne its semantics via a relational representation of XML. We then de ne an XML normal form, XNF, that avoids update anomalies and redundancies. We study its properties and show that it generalizes BCNF and a normal form for nested relations when those are appropriately coded as XML documents. Finally, we present a lossless algorithm for converting any DTD into one in XNF.

this paper, we extend XML DTDs with several classes of integrity constraints and investigate the complexity of reasoning about these constraints. The constraints range over keys, foreign keys, inverse constraints as well as ID constraints for capturing the semantics of object identities. They improve semantic specifications and provide a better reference mechanism for native XML applications. They are also useful in information exchange and data integration for preserving the semantics of data originating in relational and object-oriented databases. We establish complexity and axiomatization results for the (finite) implication problems associated with these constraints. In addition, we study implication of more general constraints, such as functional, inclusion and inverse constraints defined in terms of navigation paths

this paper. The proposal extends the key speci cation of XML Data by allowing one to specify keys in terms of XPath [24] expressions. There are a number of technical problems in connection with XPath. XPath is a relatively complex language in which one can not only move down the document tree, but also sideways or upwards, not to mention that predicates and functions can be embedded as well. The problem with XPath is that questions about equivalence or inclusion of XPath expressions are, as far as the authors are aware, unresolved; and these issues are importantifwewant to reason about keys as wedo in relational databases. Yet until we know how to determine the equivalence of XPath expressions, there is no general method of saying whether two such speci cations are equivalent. Another technical issue is value equality. XML Schema restricts equality to text, but the authors have encountered cases in whichkeys are not so restricted. See Section 7.1 for a more detailed discussion. However, the main reason for writing this paper is that none of the existing key proposals address the issue of hierarchical keys, which appear to be ubiquitous in hierarchically structured databases, especially in scienti c data formats. A top-level key may be used to identify components of a document, and within each component a secondary key is used to identify sub-components, and so on. Moreover, the authors believe that the use of keys for citing parts of a document is suciently important that it is appropriate to consider key speci cation independently of other proposals for constraining the structure of XML documents

U.C. San Diego

Abstract not found

XML specifications often consist of a type definition (typically, a DTD) and a set of integrity constraints. It has been shown previously that such specifications can be inconsistent, and thus it is often desirable to check consistency at compile-time. It is known that for general keys and foreign keys, and DTDs, the consistency problem is undecidable; however, it becomes NP-complete when all keys are one-attribute (unary), and tractable, if no foreign keys are used.

Comprehensive consistency management requires a strong mechanism for repair once inconsistencies have been detected. In this paper we present a repair framework for inconsistent distributed documents. The core piece of the framework is a new method for generating interactive repairs from full first order logic formulae that constrain these documents. We present a full implementation of the components in our repair framework, as well as their application to the UML and related heterogeneous documents such as EJB deployment descriptors. We describe how our approach can be used as an infrastructure for building higherlevel, domain specific frameworks and provide an overview of related work in the database and software development environment community.

In this article, we address the problem of how to extend the definition of functional dependencies (FDs) in incomplete relations to XML documents (called XFDs) using the well-known strong satisfaction approach.We propose a syntactic definition of strong XFD satisfaction in an XML document and then justify it by showing that, similar to the case in relational databases, for the case of simple paths, keys in XML are a special case of XFDs. We also propose a normal form for XML documents based on our definition of XFDs and provide a formal justification for it by proving that it is a necessary and sufficient condition for the elimination of redundancy in an XML document.

We present a technique for refining the design of relational storage for XML data based on XML key propagation. Three algorithms are presented: one checks whether a given functional dependency is propagated from XML keys via a predefined view; the others compute a minimum cover for all functional dependencies on a universal relation given XML keys. Experimental results show that these algorithms are efficient in practice. We also investigate the complexity of propagating other XML constraints to relations, and the effect of increasing the power of the transformation language. Computing XML key propagation is a first step toward establishing a connection between XML data and its relational representation at the semantic level.

We present a framework for publishing relational data in XML with respect to a fixed DTD. In data exchange on the Web, XML views of relational data are typically required to conform to a predefined DTD. The presence of recursion in a DTD as well as non-determinism makes it challenging to generate DTD-directed, efficient transformations.