Data, MetaData, and XML

In general, data structures are constructed with three kinds of information.

  1. The actual data in the various elements of the structure.
  2. The relationships between the various elements. (links , array position, etc.)
  3. The "MetaData".

MetaData is not as familiar as the other two so here is a brief introduction to the concept.

Working definition: MetaData is data which describes the nature of, or gives information about a datastructure.

Example: If the data structure is a book. The Data would be the text, chapter headings, title etc. The MetaData associated with the book might be the name of the publisher, the Library of Congress number of the book, or font used to print the book.

Operational Definition: The JDBC method getMetaData() returns information such as

What is XML?

 

XML is a set of rules for defining semantic tags that break a document into parts and identify the different parts of the document. It is a meta-markup language that defines a syntax used to define other domain-specific, semantic, structured markup languages.

Elliotte Rusty Harold - XML Bible

XML is ideal for large and complex documents. It not only lets you specify a vocabulary for the document, but also sets you specify the relations between elements. For example, if you're putting together a Web page of sales contacts, you can require that every econtact has a phone number and an e-mail address.

XML also provides a client-side include mechanism that can integrate date from muliple sources and display it as a single document.

Tim Bray was a prime mover in the development of X ML......Bray wanted the following:

  • a language simple enough for programmers to implement
  • a language not limited to U.S. English
  • documents easy for search engines to index
  • Elliotte Rusty Harold - XML Extensible Markup Language,
    Structuring Complex Content for the Web

 

A Simple XML document:

 

<?xml version="1.0" standalone="yes" ?>
< greeting>
      Hello World
</greeting>