Attribute Definition Lists

1
Attribute Definition Lists

• Another part of the DTD

2
What are attributes?

• Element content can be represented as attribute
  value
• Example
• ltBOOKgt
• ltISBNgtA2345lt/ISBNgt
• ltTITLEgtGrapes of Wrathlt/TITLEgt
• lt/BOOKgt
• OR
• ltBOOK ISBNA2345gt
• ltTITLEgtGrapes of Wrathlt/TITLEgt
• lt/BOOKgt

3
Where are they declared?

• Attributes declared in the DTD
• If XML document has attributes, they must be in
  DTD for document to be valid
• lt!DOCTYPE root element
• lt!ELEMENT element-name(.)gt
• lt!ATTLIST element-name Attribute-Name
  Attribute-type default-declarationgt
• gt

4
Attribute Types

• These are reserved words
• Define the nature of the attribute value
• Fall into three categories
• String
• Attribute value can be any text string
• Enumerated
• Attribute value must be selected from a list of
  possible values
• Tokenized
• Attribute value must be a valid XML name

5
String type attributes

• Simplest form of attribute value
• Form of declaration
• Attribute-name CDATA
• Example
• lt!ATTLIST CUSTOMER CustID CDATA.gt

6
Enumerated type attributes

• Attribute values are restricted to a set of
  values (enumerated types)
• Example, a customer can only be of the type
  individual or corporate
• attribute-name (value1value2value3)
• CUSTOMER CustType (homebusiness)

7
Tokenized attribute types

• DTDs support following tokens
• ID (to create a unique identifier)
• IDREF (allow attribute to reference ID of another
  element)
• NMTOKEN (name token value restricted to valid XML
  name)
• NMTOKENS (list of name tokens separated by
  blanks)

8
Tokens ID

• lt!ATTLIST CUSTOMER CustID IDgt
• ltCUSTOMER CustIDA123gtMadhult/CUSTOMERgt
• ltCUSTOMER CustIDB721gtMikelt/CUSTOMERgt
• The DTD would not be valid if both CustIDs were
  the same

9
Token IDREF

• Refers to the ID attribute of another element
• Lets say that a CUSTOMER makes an ORDER
• lt!ATTLIST ORDER Orderby IDREFgt
• ltORDER OrderbyA123gtSquash23456lt/ORDERgt

10
Token IDREFS

• What happens if CUSTOMER has more than one order?
• lt! ATTLIST CUSTOMER Orders IDREFSgt
• ltCUSTOMER OrdersA123 B345 X390gtMadhult/CUSTOMERgt
  
• All the orders must be found in the ID attribute
  of ORDER

11
Token NMTOKEN

• Similar to String
• Ensures that value of an attribute is a valid XML
  name
• Main difference is that the string cannot contain
  blank spaces
• Can be used if you wanted the attribute value to
  be a single word

12
Default Declaration

• REQUIRED
• Attribute must appear with each occurrence of the
  element
• IMPLIED
• Attribute is optional for the element
• Default value
• Attribute is optional
• If no attribute value specified, it takes the
  default value
• FIXED Default value
• Attribute is optional
• If attribute value is specified, it must be
  default value

13
What do these mean?

• lt!ATTLIST CUSTOMER CustId ID REQUIREDgt
• lt!ATTLIST CUSTOMER CustAdd (SeattleRedmondBellev
  ue) IMPLIEDgt
• lt!ATTLIST ITEM ItemQty CDATA 1gt
• Note that FIXED cannot be used for attributes of
  the type ID (why?)