XML and Web Databases

This chapter focuses on Web technologies and how they impact databases. The extensible Markup Language (XML) is perhaps one of the best known of these, and definitely the one that has had the greatest impact on databases today. A markup language is a way of indicating, in a document, any items of interest, including items such as headings, paragraph boundaries, and highlighted concepts. XML provides great flexibility in structuring information—the syntax itself imposes few restrictions and permits the complete individualization of each element occurrence. To be able to understand an XML document, one needs to know what the structure of the document is and what tags it contains. Such information about the structure of each document type is stated in a Document Type Definition. The first section of this chapter presents an overview of XML, and in the second section explores some database design issues that are specific to XML. Most databases today are accessed across the Web, so it is important to understand the impact of this context. An overview of Web technologies is given in the third section, followed by a description of the architecture of databases in websites. XML has become a very popular way to represent data and transfer it between systems. XML also underlies many important Web technologies, and therefore is important when we consider the use of databases in the context of the Web.