# Re: some minor issues in the 2nd edition documents

From: Michael Schneider <schneid@fzi.de>
Date: Thu, 27 Sep 2012 01:23:15 +0200
Message-ID: <50638E63.1060006@fzi.de>
To: Boris Motik <boris.motik@cs.ox.ac.uk>

Hi Boris!

Am 27.09.2012 00:51, schrieb Boris Motik:

>> 01) RDF Mapping: Table 11 on parsing object property expressions has now an extended condition: "OPE(_:x) = \epsilon". While I don't see an immediate problem with this condition, I don't understand why it has been introduced. In comparison, for class expressions, AFAICT, there are never any conditions on the root blank nodes. I believe it is stated elsewhere, that blank nodes for expressions must not be reused, so this condition seems redundant to me. But there may well be a reason for it.
>>
>
> If OPE(_:x) is not equal to \epsilon, then matching this pattern would redefine OPE(_:x) and we certainly don't want that.

But then, why isn't there a similar condition for the mappings of
/class/ expressions? For example, the mapping rule for class complement
expressions in Table 13 states

If G contains this pattern...

_:x rdf:type owl:Class .
_:x owl:complementOf y .
(*)    { CE(y) ≠ ε }

...then CE(_:x) is set to this class expression.

ObjectComplementOf( CE(y) )

Why isn't the condition at (*) not replaced by

(**)   { CE(_:x) = ε and CE(y) ≠ ε }

? Looks to me like being basically the same problem, or do I miss something?

Cheers,
Michael

Received on Wednesday, 26 September 2012 23:23:41 UTC

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