Terminology: Data Format versus Document Format ... and ...Extensible F

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

Hi Folks,

In his latest blog [1] James Clark makes these distinctions: 

   (1) A format for data versus a format for documents

   (2) A format that is extensible versus a format that is generalized


I want to be sure that I fully understand these terms. Here's what I think they mean:

-------------------------------------------
FORMAT FOR DATA VERSUS FORMAT FOR DOCUMENTS
-------------------------------------------

A "format for data" is a syntax that deals exclusively with fully structured data.

A "format for documents" is a syntax that deals with both fully structured data and semi-structured data (mixed content).

Example: 
    
    - JSON is a format for data. 
    - XML (and Micro XML) is a format for documents.


-------------------------------------------
EXTENSIBLE FORMAT VERSUS GENERALIZED FORMAT
-------------------------------------------

A format is "extensible" if it is a markup language which allows new markup (elements and attributes) to be added to the language.

A format is "generalized" if it is a markup language which does not have predefined tag names with built-in semantics. A format that is generalized is a meta markup language. 

Example: 

    - HTML is extensible but not generalized. 
    - XML (and Meta XML) is both extensible and generalized.


Is my understanding correct? Do the above definitions completely and correctly capture the distinctions?

/Roger

[1] http://blog.jclark.com/2010/12/more-on-microxml.html