XML in the World of (Object-)Relational Database Systems

XML is universally recognized as the standard for interchange and deviceindependent representation of information. On the other hand, XML is recently understood as a new approach to data modelling 3 A well-formed XML document or a set of documents is an XML database and the associated DTD or schema specified in the language XML Schema is its database schema. Implementation of a system enabling us to store and query XML documents efficiently is developed today in different ways. We do not discuss here native storage solution, i.e. a DBMS dedicated to manage XML data collections. A more practical possible solution can be found in storing XML data in (object-)relational DBMS. Moreover, this approach enables to provide XML with missing database mechanisms (e.g. indexes, transactions, multi-user access, etc.). Currently there is a relatively large number of works devoted to storing XML data, including the special architectures like PDOM, CMS, XML Servers, XML Query Engines, etc. We refer reader to Bourret for their comprehensive overview. Our contribution is a summarization of recent XML storage techniques based on today’s (object-)relational database technologies, their comparing and evaluation. We also present own algorithm for mapping XML Schema structures to object-relational (OR) schema. A more comprehensive discussion can be found in Mlynkova and Pokorny. For transferring the data between XML documents and (O)R structures so-called mapping methods are of a great importance. A basic classification of existing mapping methods includes the following three classes:

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