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RE: Another "Against the Grain" column on XML

Title: Message
First that document is not called algebra anymore (mainly because it describes the formal semantics). Second however, the operations are closed over the data model.
As to the popularity of XML vs relational data the points I normally make is that XML is good at representing more structured data (Ok, NF^2 systems can do this as well), semistructured data and finally combine both markup with data. The relational model itself is limited or is currently being extended into these directions (NF^2 extensions to SQL, optional columns).
I always like proof by authority though.... :-)
Best regards
'Originally, I understood [algebra] to mean a set of operations that are closed over some type. That is, every operation in X Algebra operates on zero or more values of type X and returns a value of type X...Over what is the XML Query Algebra closed? Nobody has ever given me an answer that makes sense (apart from the occasional, honest "I don't know").'
Uhh, anyone wanna try to refute that?
'[D]ue to their horrendous complexity and inflexibility, databases and DBMSs relying on the hierarchical model became obsolete  in the 80's, at least technologically. SQL DBMSs based ... on the simpler relational data model, based on predicate logic and set mathematics proved superior. ...What is the justification, then, for choosing a more complex, discredited data model for data exchange, when a majority of commonly used DBMSs employ a simpler, sounder and, thus, superior data model?'
Pascal thinks of this as the knockout punch against XML.  I think the XML advocate's response is: Codd demonstrated that the relational model is simpler to, and more powerful than, the network/hierarchical data model as a universal theory of data. Codd clearly won the "great debate" in the 1970s, but 25 years later the  skill of effectively designing properly normalized relational databases remains is a rare and valuable one, even though most of us learned the rudiments in school. Hierarchies may be unsuitable as a general, formal theory of data, but they are an easy and convenient way for humans to organize concepts (see Herbert Simon's "The Architecture of Complexity' essay) and for which effective metaphors abound (e.g., computer filesystems, formal organizations, etc.).  So, the relational model is a great formalism, but the hierarchical XML model is a convenient, intuitive, and "formal-enough" alternative.    What are some other reasons why the XML hierarchical data model is popular long after Codd discredited it as a theory of data?
Finally, 'Ironically, many of these technologies are created as "standards", purportedly to simplify and to maximize communication and integration, but the plethora of different, ad-hoc, often multiple standards achieves just the opposite.' 
Ouch, he's got us there!
Anyway, it's gotta be more interesting to think about this stuff than to debate ISO some more, eh?