XML design for relational storage

Abstract

Design principles for XML schemas that eliminate redundancies and avoid update anomalies have been studied recently. Several normal forms, generalizing those for relational databases, have been proposed. All of them, however, are based on the assumption of a native XML storage, while in practice most of XML data is stored in relational databases.In this paper we study XML design and normalization for relational storage of XML documents. To be able to relate and compare XML and relational designs, we use an information-theoretic framework that measures information content in relations and documents, with higher values corresponding to lower levels of redundancy. We show that most common relational storage schemes preserve the notion of being well-designed (i.e., anomalies-and redundancyfree). Thus, existing XML normal forms guarantee welldesigned relational storages as well. We further show that if this perfect option is not achievable, then a slight restriction on XML constraints guarantees a "second-best" relational design, according to possible values of the informationtheoretic measure. We finally consider an edge-based relational representation of XML documents, and show that while it has similar information-theoretic properties with other relational representations, it can behave significantly worse in terms of enforcing integrity constraints.

Normalization Theory for XML

“…The idea of the approach is that we measure the amount of redundancy in a design regardless of any query/update language for a data model. This approach, when applied to relational design, confirms our intuitive view of which designs are good [2,12], and then it can be applied in the case of XML to reason about XML designs for both native [2] and relational storage [13].…”

“…Theorem 5 (see [13]). An XML specification (D, F ) is well-designed for relational storage iff it is in XNF.…”

“…It is known [13] that XML functional dependencies F are translated into more general constraints over the inlined relational representation, more precisely, into a set Σ F of equality-generating dependencies. The inlining mapping also associates a position δ(p) of the relational representation with each position p in the XML document.…”

On Defining Keys for XML

“…A significant amount of data is being stored in XML either transformed from relational data and XML data(e.g.,in data publishing [3], data integration [4,5]) or created solely in XML format. Conversely, much data in XML is also being stored in relations [6,7,8]. The data * This research is supported with Australian Research Council(ARC) Discovery Project Fund and University President Scholarship(UPS).…”

Extracting a largest redundancy-free XML storage structure from an acyclic hypergraph in polynomial time

“…A recent study shows that designing XML documents for efficient retrieval and update can also guarantee well-designed relational storage structures for XML-enabled databases [13]. Thus, for both native XML databases and XML-enabled databases, designing XML documents for efficient retrieval and update is an appropriate focus for study.…”