Re: native xml processing vs what Postgres and Oracle offer

From: paul c <>
Date: Mon, 10 Nov 2008 20:20:55 GMT
Message-ID: <HI0Sk.1561$xJ3.395_at_edtnps83>

whileone wrote:
> On Nov 10, 11:40 am, paul c <> wrote:

>> Suggest that it is more accurate to say that forums are typically
>> implemented with hierarchical techniques.  It would be even more
>> accurate to say that forums are inherently ordered, eg., by date & time
>> within topic.

> I'm not sure what you point was.

Forums are *not* inherently hierarchical. You can choose to present them that way, but it's not necessary and possibly misleading.

> Yes, forum "topic headings" are ordered by date and
> time. But each topic also has 0 or more child responses, and child
> responses might
> be responses to responses, rather than responses to topic headings.
> That's a tree
> (a root node with nested children). And a tree is a hierarchy. You
> do need all those
> parent/child relationships.

Believe that if you want but there is no guarantee in any forum I've ever seen that response n, quoting response n-1, has any relationship to say, response n-2, or vice-versa. It might be seen as some kind of graph but not necessarily a tree.

(Usenet rfc 1036 dictates a generated value called MESSAGE-ID. I gather that many html-based forums can't guarantee such an attribute, maybe that complicates them. RM doesn't say anything about generated attribute values, except indirectly in the Information Principle.)

> Using relations to model hierarchies is possible but tricky (Joe Celko
> has a good book).
> With XML and XPath it is a snap. "Relational Databases" like Oracle
> and Postgres and now Mysql_5.1 (it turns out)
> do now (also) support XPath queries over XML (hybrid systems where the
> XML is stored as big
> text blob....while new system functions khow how o forget all about
> and do XPath over those blobs). The how-its-done details are a
> little more straightforward with
> 'nativel XML' databases. But conceptually (from a client developer's
> point of view) it's all
> much the same. Hierarchical XML is better at hierarchies than
> relations.

Just an aside, I suspect that these relatively low-level programming gizmos result in implementations that are just as complicated as the rarely implemented TCLOSE relational operator. One reason I think TCLOSE is fundamental is that while a relation such as {Part#, Sub-Part#} is capable of the same information content as a tree, I believe that without something akin to TCLOSE, it is impossible to express certain constraints, such as preventing cycles. Received on Mon Nov 10 2008 - 21:20:55 CET

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