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From: hidders@REMOVE.THIS.uia.ua.ac.be (Jan Hidders)
Newsgroups: comp.databases.theory
Subject: Re: database design method
Followup-To: comp.databases.theory
Date: 11 Nov 2002 19:15:58 +0100
Organization: University of Antwerp
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Paul Vernon wrote:
>
>True, but would your tree tuple example be the best way of implementing a
>tree data-structure anyway?

Implementing? This is the logical level we are talking about, so a better
word would be "modelling" or "representing" and it should IMO be up to the
user if this is how he or she wants to represent that data that way or not.

>> >What would a valid value of Tree look like?
>> >
>> >{"NodeA:Value1", ("NodeB:Value2", ("", {}) )}
>>
>> Yeah, something like that.
>
>So
>     ("", {})
>and therefore
>    {}
>would be valid values of that type? Doesn't look quite right to me.

That's why I said "something like that". :-) If you want to be precise it
should be for example:

  ( node-value : "book",
    subtrees : { ( node-value : "chapter1", subtrees : {} ),
                 ( node-value : "chapter2", subtrees : {} ) } )

and in this value the following nested values would also belong to the type:

   ( node-value : "chapter1", subtrees: {} )

   ( node-value : "chapter2", subtrees: {} )

Note that his example is a bit artificial because the chapters are more
likely to be list then a set, but that is besides the point.

-- Jan Hidders