- From: Eric Prud'hommeaux <eric@w3.org>
- Date: Tue, 2 Aug 2005 12:47:11 -0400
- To: Tim Berners-Lee <timbl@w3.org>
- Cc: public-rdf-dawg-comments@w3.org, Yosi Scharf <syosi@mit.edu>, Dan Connolly <connolly@w3.org>
- Message-ID: <20050802164711.GA8529@w3.org>
On Tue, Aug 02, 2005 at 11:27:24AM -0400, Tim Berners-Lee wrote: > > The current last call draft states, > > "A value disjunction that encounters a type error on only one branch > will return the result of evaluating the other branch." > > This seems to be a bug: inconsistent with the logic one would expect. > It is inconsistent with the general rule that the disjunction of > false with x is x for all x. The disjunction of false with a type > error is therefore a type error. If not, the type error is masked. > > Example in english: An alarm should fire if either ?smokeDetected or > the ?temperature is above 40. Suppose the ?smokeDetected is false > and the temperature is (because of a bug) bound to something which > can't be compared to 40 without a type error. The result should be > that the alarm is a type error. Instead, with the wording above, the > alarm is suppressed. I tried making this concrete, but found it supporting the spec's current wording. DATA: @prefix : <asdf> . :detector :temp \"314\"^^:degreesK ; :smokeDetects 1 . *note* degreesK is not known by this SPARQL engine and therefor is not known to be numeric and therefor throws a type error at the > operator. QUERY: PREFIX : <asdf> SELECT ?smokeDetected ?temperature WHERE { :detector :smokeDetects ?smokeDetected . :detector :temp ?temperature . FILTER (?temperature > 40 || ?smokeDetected) } RESULTS: under current semantics: [] fire:eek [] . if the type error passes through the disjunction there are no results. Does this clarify the effect of || masking type errors? Is this effect now acceptable? Would you like clarifying wording in the spec? > Yosi Scharf found also that this rule for union means that de > Morgan's laws don't hold properly, making the compilation and > optimization of queries more difficult or impossible. > > Tim Berners-Lee > MIT/CSAIL/DIG -- -eric office: +81.466.49.1170 W3C, Keio Research Institute at SFC, Shonan Fujisawa Campus, Keio University, 5322 Endo, Fujisawa, Kanagawa 252-8520 JAPAN +1.617.258.5741 NE43-344, MIT, Cambridge, MA 02144 USA cell: +81.90.6533.3882 (eric@w3.org) Feel free to forward this message to any list for any purpose other than email address distribution.
Received on Tuesday, 2 August 2005 16:47:18 UTC