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   Re: [xml-dev] Designing XML to Support Information Evolution

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On May 19, 2004, at 10:37 AM, Dare Obasanjo wrote:

> Hierarchical databases failed for a reason.

Just to be pedantic, the hierarchical model failed, hierarchical 
databases are still chugging along.  IMS (a hierarchical DBMS that is 
the meanest, nastiest, ugliest mainframe dinosaur) still quietly 
manages an awfully big chunk of the world's data:  "More than 
ninety-percent of the Fortune 1000 companies use IMS. IMS serves 200 
million end users, managing over 15 billion Gigabytes of production 
data and processing over 50 billion transactions every day."

  25 years or so ago, Codd conclusively demonstrated the superiority of 
the relational model, but  the world seems to keep reinventing 
hierarchical databases, AKA post-relational DBMS, Object-Relational 
RDBMS with an XML column type, native XML DBMS, even OODBMS (note that 
Progress has given ObjectStore new life since they bought Excelon, 
presumably because it has a lucrative niche). This happens because an 
awful lot of real-world relationships are hierarchical -- "contains / 
part-of", "parent / descendent", "manages / managed-by" .... -- and it 
is pragmatic to use tools that natively understand hierarchy to deal 
with them.  Likewise, lots of things are intrinsically ordered (time 
being the obvious one) and as best I understand it, temporal 
relationships are one of the weaker aspects of the relational model 
even in theory, nevermind practice; again, XML treats order as a 
first-class citizen and is often a pragmatic tool.


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