What Is XML?

Extensible Markup Language (XML) is a markup language for documents containing structured information. It is a simplified version of Standard Generalized Markup Language (SGML). XML has become an industry standard for delivering content on the Internet. Because it provides a facility to define new tags, XML is also extensible.Like HTML, XML uses tags to describe content. However, rather than focusing on the presentation of content, the tags in XML describe the meaning and hierarchical structure of data. This functionality allows for the sophisticated data types that are required for efficient data interchange between different programs and systems. Further, because XML enables separation of content and presentation, the content, or data, is portable across heterogeneous systems.

The XML syntax uses matching start and end tags to mark up information. Information delimited by tags is called an element. Elements can also have attributes that are defined in the form of name-value pairs.

The syntactic meaning associated with the tags of an XML document is defined in a Document Type Definition (DTD). A DTD describes the elements and attributes that are valid in an XML document, and the contexts in which they are valid. In other words, a DTD specifies which tags are allowed within certain other tags, and which tags and attributes are optional.

Schemas are a recent development in XML specifications and are intended to supersede DTDs. They describe XML documents with more flexibility and detail than DTDs do. The schema specification, currently under development, is a product of the World Wide Web Consortium (W3C) and is intended to address many limitations of DTDs.

Note: In this version of WebLogic Server, the final version of the schema specification is not supported. Therefore, the schema support in this version should be considered experimental; it should not be used in a production environment.

Why Use XML?

An industry typically uses data exchange methods that are meaningful and specific to that industry. With the advent of e-commerce, businesses conduct an increasing number of relationships with a variety of industries and, therefore, must develop expert knowledge of the various protocols used by those industries for electronic communication.The extensibility of XML makes it a very effective tool for standardizing the format of data interchange among various industries. For example, when message brokers and workflow engines must coordinate transactions among multiple industries or departments within an enterprise, they can use XML to combine data from disparate sources into a format that is understandable by all parties.