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Errors when using the --why option

From: Andrea Perego <andrea.perego@uninsubria.it>
Date: Thu, 15 Mar 2007 16:49:03 +0100
Message-ID: <45F96AEF.2060308@uninsubria.it>
To: public-cwm-talk@w3.org

Dear all,

I'm new to the mailing list and I would like to report a problem I
encountered when trying to obtain a proof from Cwm.

We are working on a rule-based mechanism for controlling the access to
resources owned by social network participants. Very briefly, the idea
is that access rules denote authorized users by using constraints on the
type, trust level, and depth of relationships. For this purpose, we
adopted the PAW approach and, in particular, we use N3 to express access
rules and the assertions on the existing relationships, whereas Cwm is
in charge of computing and verifying proofs.

We are currently implementing such system, but we found some problems in
using the --why option in Cwm. More precisely, if I run

  python cwm.py socrates.n3 --think

all works fine, and Cwm returns:

#Processed by Id: cwm.py,v 1.164 2004/10/28 17:41:59 timbl Exp
        #    using base file:/users/perego/public_html/cwm/socrates.n3

#  Notation3 generation by
#       notation3.py,v 1.166 2004/10/28 17:41:59 timbl Exp

#   Base was: file:/users/perego/public_html/cwm/socrates.n3
     @prefix : <socrates#> .
     @prefix soc: <#> .

     @forAll soc:who .

    :socrates     a :Man,
                :Mortal .
        soc:who     a :Man .

        }     <http://www.w3.org/2000/10/swap/log#implies> {soc:who
a :Mortal .
        } .


However, if I run

  python cwm-1.0.0/cwm.py socrates.n3 --think --why

here is the result:

#Processed by Id: cwm.py,v 1.164 2004/10/28 17:41:59 timbl Exp
        #    using base file:/users/perego/public_html/cwm/socrates.n3
     @@@@@@@ Proof of {} is <swap.why.FormulaReason instance at 0x824ba0c>
     @@@@@@ notation3  167 loading
file:/users/perego/public_html/cwm/socrates.n3 None {}
        Now: 169 None <swap.why.FormulaReason instance at 0x824ba0c> {}
            We have a reason for {{2}:: {who type Man} implies {who type
Mortal}} of <swap.why.BecauseOfRule instance at 0x82a070c> with bindings
{who: socrates}
        Traceback (most recent call last):
  File "cwm-1.0.0/cwm.py", line 650, in ?
  File "cwm-1.0.0/cwm.py", line 523, in doCommand
    workingContext = workingContext.collector.explanation()
  File "/users/perego/public_html/cwm/cwm-1.0.0/swap/why.py", line 128,
in explanation
  File "/users/perego/public_html/cwm/cwm-1.0.0/swap/why.py", line 141,
in explain
    ko.add(subj=me, pred=reason.gives, obj=self.formula, why=dontAsk)
  File "/users/perego/public_html/cwm/cwm-1.0.0/swap/llyn.py", line 299,
in add
    assert not isinstance(obj, Formula) or obj.canonical is obj, "obj
Should be closed"+`obj`
AssertionError: obj Should be closed{3}

With other examples, Cwm returns not an "AssertionError" but a
"NameError" ("NameError: global name 'Error' is not defined").

I've also tried to use different version of Python, but I couldn't solve
this problem. Currently I'm using Python 2.4.3 under Linux and 2.4.4
under W2K.

Could anybody help?



Andrea Perego
Dipartimento di Informatica e Comunicazione
Universita` degli Studi dell'Insubria
Via Mazzini, 5 - 21100 Varese, Italy
Received on Friday, 16 March 2007 08:37:32 UTC

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