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RE: Another "Against the Grain" column on XML
- From: Michael Rys <mrys@m...>
- To: Michael Champion <mike.champion@s...>,xml-dev <xml-dev@l...>
- Date: Tue, 07 Aug 2001 23:28:38 -0700
Title: Message
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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
Michael
'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?
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