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> -----Original Message----- > From: Subrahmanyam Allamaraju [mailto:subbu@b...] > Sent: Thursday, November 08, 2001 3:05 PM > To: Jens Jakob Andersen > Cc: lgrimaldi@n...; jens.jakob.andersen@p...; > xml-dev@l... > Subject: Re: Caught napping! > > > I don't see XML-DB proponents attempting to specify > the logical data model, the role of schema in such a model, query and > update semantics, what they mean, possible constraints (including > integrity), types (such as numbers and dates) and so on. In > the absence > of such a logical framework, the problem seems > ill-defined/under-specified to me. XML does not claim to be a general theory of data; it does not compete in that respect with the relational model, so it's not "ill-defined/under-specified". You're right about the "update semantics;" I assure you from working on the DOM specs that XML 1.0 is has a read-only orientation baked deep into it. Types, of course, are a well-known issue that is supported in the Schema layer on top of XML itself, and are admittedly still a bit bleeding edge. BUT XML is suitable for a particular class (a large one!) of problems where relationships are defined hierarchically -- "IS-A", "PART-OF", etc. and the "document", not the elements/attributes in it, is the basic unit of work. In this class of problems, integrity constraints and update semantics are not salient issues. In that class of problems, XML databases can be quite appropriate solutions because they do not force one to consider the logical-physical mapping: Native XML databases store data (either physically or via intermediate data structures that are invisible to the user) in essentially the same form that is seen by the end user, hence "database" modelling is essentially the same as "document" modelling as practiced by the SGML folks for some time. This has a cost in flexibility -- you don't get the benefits of data independence, such as ease of re-use of one physical database by multiple applications with different logical views -- but a lot of practical benefits in terms of performance, ease of mapping onto XML interface standards, lower cost of DB administration, etc.
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