Streaming XML Schema Validation for Relational Tree Encodings

Abstract

The Extensible Markup Language (XML) is a plain text format, widely used to store and exchange documents possessing a hierarchical structure. The wide-spread use of XML as a data storage and exchange format imposed an emerging need for storing XML documents in databases. Since there are mature relational database management systems available, an obvious approach is to transform the tree shaped XML documents into tables and store them inside the RDBMS.XML Schema is another W3C specification, allowing the description of structure and semantics of XML documents by means of regular expressions and context free grammars. The process of verifying whether an XML document fulfills a Schema definition is called validation.This diploma thesis introduces a new way of validating relationally encoded XML documents against XML Schema definitions.The proposed algorithm is based on the concept of deriving a regular expression. Hence, it is neither necessary to reconstruct the XML tree from its encoding, nor to build a finite state automaton from the XML Schema definition. Moreover, the encoded tree is read as a stream, i.e., exactly once, sequentially in document order.This thesis introduces guards, an amelioration of regular expressions which integrates information about the hierarchical structure of trees. The concept of derivation is augmented to make use of the pre/post enumeration and the enriched regular expressions.This diploma thesis comes with "http://www.ub.uni-konstanz.de/kops/volltexte/2004/1234/pdf/impl.tar.gz" an implementation of the proposed algorithm, written in the functional language Haskell.