[sc34wg3] TMQL, State of Affairs

[Jan Algermissen]

On May 23, 2005, at 10:32 PM, Jan Algermissen wrote:



>
> On May 23, 2005, at 10:21 PM, Martin Bryan wrote:
>
>
>
>
>>  why yet another query language is needed, and why XQuery or
>> somehting based on the tried and tested ISO-standardized SQL  
>> approach would
>> not do just as well.
>>
>>
>>
>>
>
> Hi Martin,
>
> a query language is neccessarily defined in terms of an underlying  
> data model (data model in
> the sense that the relational model is a data model and not in the  
> sense 'domain model').
>
> Xquery is based on the DOM (XML heads correct me please), SQL is  
> based on the relational model
> (on relational calculus and relational algebra).
>
> Topic Maps [1] are a completely different data model so you need a  
> new query language.
>
>

Hmm...another way to say this is:

If you can apply relational algebra or calculus to a TMDM-style graph  
you can use SQL as
a TMDM query language. But yoou can't, because TMDM style topic maps  
are graphs and not
collections of relations.

Similar for XQuery, because XQuery operates on a tree and not on a  
graph.

HTH,

Jan




>
> Jan
>
> [1] TMDM (part of it) definitely is a data model and IMHO the RM  
> has allways been one, too
>     (though the current authors disagree with me on this).
>
>
>
>>
>>
>>
>>
>
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