Specifying scope of uniqueness in XML Schemas?

Henry S. Thompson ht at cogsci.ed.ac.uk
Mon Jan 3 17:29:59 GMT 2000

Roger Costello <costello at mitre.org> writes:

> In section 3.7 of the XML Schema spec it talks about the mechanism for
> indicating uniqueness (of elements, attributes, or combinations
> thereof).  It says that you can specify uniqueness within a region, or
> over the entire document:
> "Constraints can be specified to have document-wide scope or to hold
> within the scope of particular elements."
> Can someone explain to me how you indicate the scope of a constraint?  I
> am guessing that it is with the selector element, but I am not sure. 

Sorry this isn't clearer:  The scope is indicated by where the
declaration goes:  if I put a <key> element within an element
declaration for an element named 'foo', then the uniqueness and
ubiquity constraints obtain within each <foo>...</foo> in a document.

The <selector> tells you which elements WITHIN each <foo> must have keys.

  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht at cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/

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