What is XML or Extensible Markup Language?
XML (eXtensible Markup Language) is a less complex, more concise dialect of the larger more complex SGML (Standard Generalized Markup Language). In the simplest terms XML uses syntax tags to identify various types of data in a file. For example: XML makes it very easy for various programs to extract data because the tags conform to particular models. Above we see a data model with 7 elements: Client (parent element), contains 6 nested elements: name, street, city, state, zip and phone. Name: XML-aware programs know this field holds the name of a person or company. Street: This field will hold a street address. City: Here it will find the city. State: The abbreviated 2-letter state code. Zip: The 5-digit zip code. Phone: And the phone. To define the data model or content of each of the elements a DTD (Document Type Definition) can be used. A DTD is one way to define the structure or tree of an XML document. A DCD (Document Content Description), DDML (Document Definition Markup Language)
