The history of the databases is closely related to the data models and database systems. Everyone knows the path to their formation, the CODASYL recommendation, the main stages of development, which actually followed through hierarchical network and relational way of mesh data models. Longer carry the '90s and the new millennium marks the achievements. Progress is slowed down, but not stopped. Upon receipt of the object-oriented approach, the next higher step was the inclusion of XML languages and technologies.
In 1999, Tim Berners-Lee – the founder of WWW - has presented his latest idea of the Semantic Web agenda. It brought with it the ubiquity of XML languages and simultaneously published the first databases based on XML documents. The XML database management systems are basically not or do not typically store data in XML structures (to avoid unnecessary waste of space due to the lengthy XML document). The situation here is similar to a typical ANSI database architecture: again, not the physical but the logical database structure has changed.
For querying XML documents, the W3C consortium created a working group and two recommendation: the XPath and the XQuery language were born, these are based on a common data model from version 2.0. The reason of proliferation of XML-based databases, is that today not the users but software's (B2B) are producing and processing automatically and semi-automatically messages / queries. In this picture, the XML is well suited as a tool for data exchange. XQuery and XPath-based solutions to meet such requirements is much better than the SQL-based systems, in which data must be transferred to the transformation process is costly.
The purpose of this book means description of this world and demonstration of the use of XML in databases. The book does not aim to solve the problems of the storage of XML documents, just concentrate on the application approach. Complex methods exist for storing XML documents, a number of experimental systems exist which are beyond the scope of this book.
However, review of the structural design of the different approaches and the advantages and disadvantages of a new XML document in the book must part, because this is the point where you should learn about the various opportunities offered by these techniques in order to be able to work effectively document structure. In addition, we present validation, because a database is not simply a collection of data, but also help formulate complex rules to monitor the constraints on the stored data. To do this, we will also use standard technologies.