DTDs are described in the XML specification. If the validation is successful the document is said to be valid XML based on the particular DTD . If a DTD is not present and the parser does not encounter syntax errors parsing the file, the XML document is said to be well-formed . If errors are found, the document is not XML compliant. Let's consider an example.
Search engines spring up across the net to help find documents.
Search engines have a difficult time searching specific pieces of a document since HTML was designed to represent hierarchically how data should be presented, but not what data is being presented. Web applications spring up across the net to provide information and services . These services could be web pages that serve up important information about an organization or the structure of the organization. It could be weather information or travel advisories. It could be contact information for people.