I am quite new to both RDF and Redland, and so I managed to find a bug
straight away.
I have installed redland-1.0.4 using redland-bindings-1.0.4.1 and rasqal-0.9.12.
I am using redland through the Python bindings, which seems great.
With a mysql backend, the following script "corrupts" the backend:
import RDF
_options_string="""host='localhost',
user='repository', password='fishme',
database='repository'"""
storage = RDF.Storage(storage_name="mysql", name="fish",
options_string=_options_string + ", new='true'")
model = RDF.Model(storage)
#model = RDF.Model()
# A normal thing
subject = RDF.Uri("mailto:[EMAIL PROTECTED]")
predicate = RDF.Uri("http://soiland.no/likes";)
object = RDF.Node("Gaby")
model.append(RDF.Statement(subject, predicate, object))
# A weird one, using a Literal as a subject!
subject = object # ie. "Gaby"
object = RDF.Node("Stian")
model.append(RDF.Statement(subject, predicate, object))
# And this is a normal one again
subject = RDF.Uri("mailto:[EMAIL PROTECTED]")
predicate = RDF.Uri("http://soiland.no/kisses";)
object = RDF.Node("Gaby")
model.append(RDF.Statement(subject, predicate, object))
# Should now print 3 lines, or at least 2
for s in model:
print s
This will print out just *1* statement. As a fresh user it was kind of
difficult to understand what was wrong at first, but the I realized I
had added a Literal as a subject. Both subjects and predicates should
be RDF.Uri objects, not literals.
It seems that adding the illegal statement works fine, inspecting the
database manually yields all statements and literals, even #3.
However, when fetching things back, RDFlib will stop when coming to
the illegal statement #2. This is confirmed to be a problem in the C
backend by calling the functions Redland.librdf_stream_get_object and
librdf_stream_next manually.
Note that if you switch to the memory model (uncommented in this code)
everything works, even adding the illegal statement.
If you switch to the sqlite backend instead you'll get a SQL error instead:
: [EMAIL PROTECTED] ~;python problem.py
Traceback (most recent call last):
File "problem.py", line 22, in ?
model.append(RDF.Statement(subject, predicate, object))
File "/usr/lib/python2.4/site-packages/RDF.py", line 748, in append
self.add_statement(statement, context)
File "/usr/lib/python2.4/site-packages/RDF.py", line 732, in add_statement
statement._statement)
RDF.RedlandError: 'SQLite database fish SQL exec \'SELECT COUNT(*)
FROM triples WHERE =1 AND predicateUri=2 AND objectLiteral=2;\' failed
- near "=": syntax error (1)'
I guess if predicates and subjects can't be literals, this should be
enforced when creating or adding the statement.
But as this has worked for memory models and for adding to mysql
backends, the storage should be able to read back such stuff.
Btw, the _options_string is a bit weird, is there a nice way to use a
normal dict()?
--
Stian Søiland Any society that would give up a little
Manchester, UK liberty to gain a little security will
http://soiland.no/ deserve neither and lose both. [Franklin]
=/\=
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