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Re: [DM] BEA_004

From: Norman Walsh <Norman.Walsh@Sun.COM>
Date: Wed, 25 Feb 2004 10:55:53 -0500
To: public-qt-comments@w3.org
Message-id: <87eksji25y.fsf@nwalsh.com>
/ Daniela Florescu <danielaf@bea.com> was heard to say:
| Data model: editorial, minor
| section 2.2. mentions parent as an example of partial function.
| That's a wrong use of the mathematical concept of partial function.
| A partial function is undefined on a subset of the domain (and
| expected to raise
| errors on this subset), while the parent function does return values on
| all the nodes. It is true that sometimes the result is the empty
| sequence, but this
| doesn't make it a partial function.

I don't think the phrase "partial function" actually adds any value to
the explanation. I've reworded it as follows:

<p>There are some functions in the data model that return the empty sequence
to indicate that no value was available.
We use the occurrence indicators <emph>?</emph> or
<emph>*</emph> when specifying the return type of such functions.
For example, a node may have one parent node or no parent.
If the node argument has a parent, the
<function>parent</function> accessor returns a singleton sequence.  If the node
argument does not have a parent, it returns the empty sequence.
The signature of <function>parent</function> specifies that it returns
an empty sequence or a sequence containing one node:</p>

Please let me know if this satisfies your concern.

                                        Be seeing you,

Norman.Walsh@Sun.COM / XML Standards Architect / Sun Microsystems, Inc.
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Received on Wednesday, 25 February 2004 10:56:14 UTC

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