• To: www-xml-schema-comments@w..., xml-dev@l...
• Subject: nillable keyrefs in XSD
• From: ari@c... (K. Ari Krupnikov)
• Date: 21 Feb 2003 17:01:50 +0000
• User-agent: Gnus/5.0808 (Gnus v5.8.8) Emacs/20.7

As far as I understand, keyrefs in XSD must always point to a valid
key in the instance document; there is no parallel to a C null pointer
or an SQL NULL foreign key, IOW, one cannot say, "this element *may*,
point to another element, but is not required to".

It seems that I can model this SQL in XSD:
FOO INTEGER NOT NULL REFERENCES BAR.BAZ

but not this:
FOO INTEGER NULL REFERENCES BAR.BAZ

Ari.

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