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

[Rick Jelliffe <rjelliffe@allette.com.au>]

Costello, Roger L. wrote:
> 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. 
>   
Better:   XML defines the notation of the markup and data in a document. 
XML specifies the syntax, not the semantics of the document.
> 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.
>   
OK
> 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.
>   
OK
> 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.
>   
Better: Markup that is concerned with annotating information, for 
example, with identifiers, is descriptive markup. The document may form 
a database which is independent of any particular application.
> 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.
>   
Better: Markup that is concerned with specifying  the recipe to be 
followed in order to achieve a result is algorithmic markup. XML 
documents are rarely of this kind, since programming languages are 
well-established with optimized syntax for programming. The main 
exception is XSLT, which allows some algorithmic features such as 
functions.

Cheers
Rick Jelliffe