RE: XML and the Relational Model (was Re: A standar
I think we can try to answer what advantages do XML provide when we try to use it for DB applications? I will initiate it with my opinions.. (a) XML schemas provide union types and recursive types, which are convenient.. union types: for example, we can say that book has title or ISBN no. recursive types: we can say part in turn contains other parts. Union types help us understand more semantics of data, recursive types allow us to define recursive operators like "//" if we try to write a recursive query in SQL 99, it is quite difficult. So in general I will say XML provides structures which might be convenient for our applications.. (b) XML also allows us various ways of representing relationships: like parent-child, IDREF, or foreign keys. Each representation might be "convenient" for the user for different applications.. (c) As someone mentioned before, try for a federated DB to use relational as the unified view of the different sources, it gets so difficult to do so, because relational does not give us flexibility... XML might give some more flexibility needed for our application.. (d) Consider the case where data stored in our DB includes structured portion as well as semi-structured (text) portion.. for example, for each employee, you store attributes like his DofB, salary etc, and also, we have a column where we want a description of the person, which could be in XML.. I hope there are applications which require (d).. best regards - murali.
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