DTD

Attributes vs. Elements:

attributes

elements

represent atomic data represent structured data

usually represent properties of object represent parts of object

can represent relationships (ID/IDREF types) can represent relationships by including one element into another

often represent data that is less important, or data about data

may appear only once on an element my appear many times inside another element

appears at no guaranteed order, as a set may be required to appear in specified order

cannot be "extended" by adding sub-attributes can be extended by adding sub-elements

must have unique name within an element There can be several elements with the same name inside another element

values are often short and simple values can be long

make document concise make document verbose

cannot contain <![CDATA[ blocks. can contain <![CDATA[ blocks.

cannot have external parsed entities as a value can have external parsed entities as a value

can have external unparsed entities or notations as a value (if declared of ENTITY, ENTITIES, NOTATION type) no?

All below was written with DTDs in mind

can be validated to have enumerated values (from a list) cannot

can be validated to have unique values cannot

can have default values cannot

References:

1. Beginning XML. David Hunter, Curt Cagle, Dave Gibbons, Nikola Ozu, Jon Pinnock, Paul Spencer. Wrox Press Ltd.

2.When Should I Use Elements, and When Should I Use Attributes?
http://www.oasis-open.org/cover/elementsAndAttrs.html

3. The Attribute/Text Conundrum. "Document-Centric" vs. "Data-Centric"
http://www.xmleverywhere.com/newsletters/20000525.htm

Quotes:
"Elements and attributes are both containers for information. Many times the choice between an element and an attribute seems very arbitrary, almost matter of style. While the choice may indeed be arbitrary in some cases, the 'typical' roles of elements and attributes and the different types of content models and constraints these two containers support may tip the scales in one direction or the other."
http://www.devguy.com/fp/XML/dtd.htm

"Use attributes when you can, and elements when you have to
Advantages:
· Makes the document easier to process using SAX or the DOM
· Makes documents smaller and therefore documents can be processed more efficiently
This rule is fairly self-explanatory. Not everyone is convinced that this is the best way. Arguments against attributes usually assert that elements are easier for humans to read. However, attributes lead to significant performance improvements when processing is involved. The advantages of attributes can not be ignored if scalability is a priority."
http://www.xmleverywhere.com/tips/designTips.html

attributes	elements
represent atomic data	represent structured data
usually represent properties of object	represent parts of object
can represent relationships (ID/IDREF types)	can represent relationships by including one element into another
often represent data that is less important, or data about data
may appear only once on an element	my appear many times inside another element
appears at no guaranteed order, as a set	may be required to appear in specified order
cannot be "extended" by adding sub-attributes	can be extended by adding sub-elements
must have unique name within an element	There can be several elements with the same name inside another element
values are often short and simple	values can be long
make document concise	make document verbose
cannot contain <![CDATA[ blocks.	can contain <![CDATA[ blocks.
cannot have external parsed entities as a value	can have external parsed entities as a value
can have external unparsed entities or notations as a value (if declared of ENTITY, ENTITIES, NOTATION type)	no?
All below was written with DTDs in mind
can be validated to have enumerated values (from a list)	cannot
can be validated to have unique values	cannot
can have default values	cannot

References: 1. Beginning XML. David Hunter, Curt Cagle, Dave Gibbons, Nikola Ozu, Jon Pinnock, Paul Spencer. Wrox Press Ltd. 2.When Should I Use Elements, and When Should I Use Attributes? http://www.oasis-open.org/cover/elementsAndAttrs.html 3. The Attribute/Text Conundrum. "Document-Centric" vs. "Data-Centric" http://www.xmleverywhere.com/newsletters/20000525.htm
Quotes: "Elements and attributes are both containers for information. Many times the choice between an element and an attribute seems very arbitrary, almost matter of style. While the choice may indeed be arbitrary in some cases, the 'typical' roles of elements and attributes and the different types of content models and constraints these two containers support may tip the scales in one direction or the other." http://www.devguy.com/fp/XML/dtd.htm
"Use attributes when you can, and elements when you have to Advantages: · Makes the document easier to process using SAX or the DOM · Makes documents smaller and therefore documents can be processed more efficiently This rule is fairly self-explanatory. Not everyone is convinced that this is the best way. Arguments against attributes usually assert that elements are easier for humans to read. However, attributes lead to significant performance improvements when processing is involved. The advantages of attributes can not be ignored if scalability is a priority." http://www.xmleverywhere.com/tips/designTips.html