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Re: XQuery and Hypertext (was Re: SGML on the Web

• To: mc@x... (Mike Champion)
• Subject: Re: XQuery and Hypertext (was Re: SGML on the Web
• From: John Cowan <jcowan@r...>
• Date: Thu, 10 Oct 2002 13:53:57 -0400 (EDT)
• Cc: xml-dev@l...
• In-reply-to: <KI53HFQGDLI74GFY4TPQLA7KJFCVU.3d9e0501@MChamp> from "Mike Champion" at Oct 04, 2002 05:15:45 PM

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@r...
banging their head against?  --Larry            http://www.ccil.org/~cowan

• References:
  • XQuery and Hypertext (was Re: SGML on the Web
    • From: Mike Champion <mc@x...>

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