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XML Concepts : Page 3

XML is way of marking up data, adding metadata, and separating structure from formatting and style. Web pages are just one of many uses for XML.


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Metadata
Metadata is data about data. A key use of XML is to collect and work with metadata.

At its most basic level, XML is a metadata language. That is, it is a way of assigning information to pieces of data. The most obvious use of this is to identify a piece of data as a certain structural element. But this is just the beginning.

XML is about much more than marking up documents for use in a Web browser. XML is really about adding layers of information to your data, so that the data can be processed, used, and transferred between applications.



Metadata in HTML
If you've built a Web site, you've almost certainly worked with metadata. The keyword and description meta tags are simple uses of metadata. With these meta tags you can assign the document as a whole information about the general type of content it contains. This information doesn't display in a Web browser, but it does display in search engine results.

Another use of meta tags is to store information such as creator name and creation date. Some servers are structured to work with these meta tags, allowing you to sort by creation date or display based on creator name.

Going Further with XML
XML takes this basic idea much further. With XML, you can describe where you found your data, you can quantify, qualify, and further define it. You can then use this metadata to validate information, perform searches, set display constraints, or process other data.

Here's just a few examples:

  • XML initiatives are under way which will allow for digital signature verification and validated form submission. This could make it possible for forms, with signatures, to be submitted online and be legally binding.
  • XML initiatives are under way to help catalog Web content. Using metadata, the Web can be be indexed better and search more effectively.
  • XML is being used to transfer data, based on factors just as date entered, between unlike databases. The metadata is both a means to find the correct data bits and a common language of transfer between databases which do not speak each other's specific language.

The RDF Proposal
One W3C-blessed use of metadata which you may have heard about is a proposal called the Resource Description Framework, or RDF. RDF is an application of XML for making metadata machine-processable. It allows applications to exchange information about data automatically. This has implications in indexing, content rating, intellectual ownership, e-commerce, and privacy, among other things. The W3C says:

RDF with digital signature will be the key to building the "Web of Trust" for electronic commerce, collaboration, and other applications.





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