Document Type Definitions

• A DTD is a set of rules for correctly formed documents of a particular type
  • Describes the valid attributes for each element type
  • Describes the valid child elements for each element type
• Valid child elements are described by an ELEMENT rule

  <!ELEMENT items (item*)>
  

• The items element can have 0 or more item elements
• Definition of an item node

  <! ELEMENT item (product, quantity)>

• Children of the item node must be a product node followed by a quantity node