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   Re: [xml-dev] XQuery and Hypertext (was Re: [xml-dev] SGML on the Web

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Mike Champion scripsit:

> The key differentiator was that CODASYL ultimately
> relied on "pointers" (which I'm pretty sure are functionally much like
> hyperlinks, at least by analogy) to relate bits of information that did
> not fit into a hierarchy, 

Actually, the CODASYL model was about multi-hierarchies, with none
preferred.  Here's how you'd do the CODASYL model on a relational DBMS,
which is historically backward, but a lot more people understand RDBMSes.

Data is kept in objects like relational tables, except that the primary
key is always a generated unique ID.  (Implementationally, this was
an address.)

Then there would be linkage tables, potentially one per pair of tables,
with the fields <primary key 1>, <primary key 2>, <sort order>.  (This was
implemented as a linked list of primary-key-2s starting from the record
labeled by primary-key-1.)  All navigation must be done through these links.

What is the sound of Perl?  Is it not the       John Cowan
sound of a [Ww]all that people have stopped     jcowan@reutershealth.com
banging their head against?  --Larry            http://www.ccil.org/~cowan


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