RE: [xml-dev] What is declarative XML? (And what's not)

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,

I'd like for us to nail down exactly what we mean by "descriptive markup" and "algorithmic markup." Here's a stab at it:


1. XML documents just contain markup and data. There are no semantics in XML documents. An XML document is just syntax.

 
2. A software application can be written to perform specific, repeatable actions when it encounters markup in an XML instance document. Stated differently, applications can be written to add a layer of semantics on top of the XML syntax.


3. When creating an XML vocabulary, it is common practice to write prose that specifies semantics for the XML vocabulary. Then software applications can be written to implement the semantics specified by the prose.


4. Sometimes the prose just assigns a definition to each element and attribute in the XML vocabulary. Software applications that implement these semantics "understands" the XML vocabulary. These applications don't execute any actions when given an XML instance document, beyond simply informing itself. For these applications the markup is purely informational or descriptive. 

    For applications faithful to the semantics 
    specified by the prose, the XML vocabulary 
    is descriptive markup.


5. Sometimes the prose associates actions to each element and attribute in the XML vocabulary. Software applications that implement these semantics will execute the actions when given an XML instance document. For these applications the markup represents instructions or prescriptions. 

    For applications faithful to the semantics 
    specified by the prose, the XML vocabulary 
    is algorithmic markup.


I'm sure that these can be expressed more clearly. I welcome your suggestions.

/Roger