From: Richard Knapp (richfk_at_attglobal.net)
Date: Thu Jul 18 2002 - 12:49:14 CEST
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On Thu, 18 Jul 2002 17:44:22 +1000, Peter MATTHEWS wrote:
> At 18:27 10-07-02 -0400, Richard Knapp wrote:
> [snip]
> >Under Branch, there is a field of Node type however, Node is an Element not
> >an attribute.
>
> The fields shown under Branch are actually called "node names", i.e. the
> names of the Nodes which terminate/define each end of the Branch. These
> names are therefore properties of the Branch.
Are the names unique to the system? How will that be ensured? If IDs
are used, how will their uniqueness be ensured? If multiple files are
joined - a previously unrelated cave was connected - how will the
uniqueness transfer into the newly joined files?
> >The diagram shows a many-to-many relationship. How is this going to work?
>
> To be honest, as a "beginner" XML person I am not sure of the details. Can
> anyone else give an XML example? However, if two real-world things actually
> are related many-many, then XML needs to be able to handle it, somehow.
Only if they turn out to be true relationships. We are in the process
of discovering "entities", "fields", and "relationships". And there
is no guarantee that implementation will match design.
> Like with databases, I suspect you would just show or record one direction
> at a time, depending on what was the context of the file/document you were
> creating.
In XML, you can use IDREFS to indicate a list of IDs in an attribute.
However, attempting to work with IDs in a more basic circumstance
(Stations) proved very difficult. And again the requirement that IDs
are unique (document wide) is limiting, especially when you consider
joining files.
> For example, taking the case of say the two entities, People and
> Organisations, which have a many-many relationship: one Person can belong
> to many Organisations, and one Organisation can have many People as ...
These are model and design decisions. I could just as easily say
Organizations are made up of People and leave it at that. If I want
to find what organizations someone is in, I could scan the
Organizations for that person. Not efficient but it would work... Or
the other way around.
> In the diagram, I have shown [cavesystem] as the top of the hierarchy -
> [caves] are within [cavesystem], and [projects] are within [cavesystem].
So Cave and Project are at the same level, or can there be a project
within a cave as well? What if there is no cavesystem, I'm just
working on a cave (most likely scenario)? Wouldn't the highest level
be the document? (in XML, the root element - CaveXML; in RDBBS, the
database). From that can spawn a Project consisting of multiple caves
or a cave system with multiple caves and projects or a cave with
multiple projects or....
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