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This is a cheat sheet for the DTDlanguage. It is a follow up to theXML Cheat Sheet and summarizesthis DTD Tutorial. There is also an XML Schema Cheat Sheet.

For reference this is the XML Specification (which also documentsDTD) and the version annotated by Tim Gray.

• A Document Type Definition (DTD) defines the legal building blocks of an XML document. It defines the document structure with a list of legal elements and attributes.
• A DTD can be internally defined e.g.

or externally defined e.g.

where the element-declarations are in filename.dtd

• A simple example of DTD element-declarations

This says that note contains 2 child elements and to and from are of type #PCDATA .

• A DTD for an XML document may contain the following building blocks

• elements
• attributes
• entities (e.g. character entities)
• PCDATA (parsed character data parsed for entities and markup)
• CDATA (character data that is not parsed)

DTD Elements

• An element is defined as

or

• category can be either EMPTY or ANY
• element-content can be any combination of #PCDATA or child elements
• child_element+ – one or more occurrences
• child_element* – zero or more occurrences
• child_element? – zero or one occurrences
• (a|b) – Either a or b (can be #PCDATA)
• a,b – a and then b in that order

DTD Attributes

• An attribute specified in a DTD takes the form

for example:

• attribute-type can be one of the following

• CDATA – character data
• (en1|en2|..) – one from an enumerated list
• ID – a unique id
• IDREF – the id of another element
• IDREFS – a list of other ids
• NMTOKEN – a valid XML name
• NMTOKENS – a list of valid XML names
• ENTITY – an entity
• ENTITIES – a list of entities
• NOTATION – a name of a notation
• xml: – a predefined xml value

• value – the default value of the attribute
• #REQUIRED – attribute is required but with no default
• #IMPLIED – attribute is optional and with no default
• #FIXED value – the attribute value is fixed

DTD Entities

• Entities are variables used to define shortcuts to standard text or special characters.
• Entities are declared in DTDs and can be declared internal e.g.

or external e.g.

• Entity references are references to entities and may be used inXML documents.
• An entity reference has three parts: an ampersand (&), an entity name, and a semicolon (;). e.g.