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   Re: [xml-dev] XML and the Relational Model [long]

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[Jeff Lowery]

> TPassin>
> > * When is it better to store data in an XML format than in a relational
> > format - no fuzzy generalities, but a real discussion, please!
> What I'm saying is that there is no "relational format", so to speak.
> are storage formats optimized for general relational operations, but that
> doesn't mean that other storage formats cannot support them.

Just sloppy language on my part, I know that "relational" does not mean a
storage format.  I did not really mean storage of bytes, but was thinking of
the logical (or conceptual, if you like) level.

For example, it is easy to model a two-level hierarchy in SQL, but it is
awkward to model (and query) a hierarchy of an indefinite number of levels.
So when the data model is deeply hierarchical, xml structures might have an

If the data model is sparse, xml may be much better than a table-like model.
Similarly when the contents of an element type may vary quite bit from one
instance to another.

On the other hand, if you create a well-normalized data model to begin
with - when that is practical - you could probably implement it either with
xml or with a relational database.  What are the differentiators between
going one way or the other?


Tom P


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