XML has been called everything from the technology that will revolutionise the Web to a nuisance. What's really the story?
XML--Extensible Markup Language--provides a way of marking up a document that reflects the structure of the information it contains. While HTML is concerned primarily with the way the document is presented (eg, that a certain array of information is to be presented in a table with a certain number of rows and columns), it doesn't say anything about the nature of the item in each cell. This makes it difficult to write a robust program to do anything with an HTML document apart from displaying it.
If you know that a table contains a list of products and column one holds the description and column two the price, that's fine. But what happens if the organisation producing the document adds a column to flag new items, and description and price end up in columns two and three? An XML document includes definitions (or references to external definitions) for the data it contains, so there's no requirement for the receiver to know or guess anything about the data.
And, as assistant professor John Hurst of Monash University's School of Computer Science and Software Engineering points out, it is relatively easy to restructure data expressed in XML. "It gives the user far more flexibility and choice...in that context, XML beats everything else hands down," he says.
