[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Some random noise on rational type systems for XML
> I don't think you mean "the absence of a tuple". The relational model > has the vast edifice of "null" to support absent data in a cell of a > table, but it has never had any way of representing a missing or unknown > row. This depends on whether on not you are making what C.J Date calls the "Closed World" assumption about your relational database (which he prefers to). Thus the absence of a particular row in a relation is taken to imply the falsity of the predicate that relation represents. If your employee relation has no record for "Gary Stephenson", it is assumed to be true that I am _not_ an employee of yours. I think we often make this assumption implicitly about our databases, without properly appreciating the implications thereof for normalization etc. > An element with empty content is surely the parallel of a cell > containing a zero-length string in SQL. Users may use this with similar > semantic intent to omission of the element, but it's hard to see it as > an analog of SQL's NULL. And may the <deity_of_choice> be praised for that! > For my part, I have always thought that xsi:nil is an abomination. ditto SQL NULLs (imho) gary
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