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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."
http://www-306.ibm.com/software/data/ims/highlights/experform.html
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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