[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
In XML there are three (not two) syntactic devices that people have at various times asserted have some connection to the absence of a tuple in the relational model. XML has: 1. Omission of an optional element. 2. Presence of an element having the attribute xsi:nil 3. Presence of an element having empty content. SQL does make a distinction between omission and NULL in some contexts (e.g. an UPDATE statement) but not in others (e.g. a rowset). -----Original Message----- From: Jeff Lowery [mailto:Jeff.Lowery@c...] Sent: Tuesday, May 06, 2003 3:45 PM To: 'Amelia A.Lewis'; xml-dev@l... Subject: RE: Some random noise on rational type systems for XML > The SQL people > encountered this, and found a solution, which made them > heretics in the > eyes of the relational true believers. The problem is that > whenever you > have a thing that has a value, it is often useful to be able to say > "don't know" "not specified" "undefined" "null" or "nil". W3C XML > Schema introduces a mechanism for this. So, umm, why? XML > already has > a way to say nothing. Say nothing. The empty string. No data. Not > specified. I would say "data is undefined" and "data does not exist" are two different things. SQL treats NULL different from an empty string. For XML, null would seem not to be necessary for numbers, since 'empty' would not necessarily be interpreted as zero. > Heh. But this is already too long, and besides, I *enjoy* > cliff-hangers, so let's just Tune In Next Week for Another > Bland Episode Spring: the silly season. ----------------------------------------------------------------- The xml-dev list is sponsored by XML.org <http://www.xml.org>, an initiative of OASIS <http://www.oasis-open.org> The list archives are at http://lists.xml.org/archives/xml-dev/ To subscribe or unsubscribe from this list use the subscription manager: <http://lists.xml.org/ob/adm.pl>
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