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Subject: Uses for and classifications of attributes


As per a request from last week’s meeting:

 

Attributes are a way of attaching extra information to XML elements. Attributes are most important where one must make a principled distinction between content and metadata. This is especially common in document-oriented DTDs and schemas where content and metadata tend to have different properties:

 

 

Content

Metadata

Content handling by formatter

Shown by default

Hidden by default

Appropriate DITA base classes

Specialized from some body content element.

Specialized from an attribute or metadata element.

Can influence parent element’s formatting in CSS

Yes

No

Can have child elements

Yes

No

Can be safely discarded by processes that do not recognize it

Seldom

Usually

Explicitly defaultable in XML 1.0

No

Yes

 

Common types of attributes:

  • URLs (CDATA)
    • Semantically-oriented elements (e.g. employee records) may have references to other internal systems or related elements elsewhere
  • References to names defined elsewhere NMTOKENS
    • e.g. product names, SKUs, programming language keywords, etc.
  • Filtering attributes (NMTOKENS)
    • As per DITA 1.0
  • Title-like attributes (CDATA)
    • E.g. HTML’s “alt” attribute, DITA’s “navtitle” attribute.
  • Numeric attributes (NMTOKEN)
    • E.g. a picture’s optimal viewing width and height, the latitude and longitude of a location, the price of a product.
  • Categorization attributes (NMTOKEN)
    • For example, Docbook’s citebiblioid attribute allows the user to define the type of identifier that was used: “isbn”, “issn”, “libraryofcongress” etc.
    • In Docbook, an organization can be “consortium”, “corporate”, “not-for-profit” or “informal”
  • Formatting-oriented attributes (enumeration or NMTOKEN)
    • E.g. align left, align right, etc.
  • Repository identifiers (CDATA)
    • Repository may work at more granular level than file. Then repository identifiers could appear on any element.

 



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