On 24/08/12 16:24, Simon Helsen wrote:
Andy,
Although this is perhaps a matter of taste, I discussed this issue with a
few smart people here who all intuitively assumed that
unionDefaultGraph=true would automatically merge graphUri2 into the
default graph even if explicitly defined as in the following query:
FROM <graphUri1>
FROM NAMED <graphUri2>
Then I am clearly not a smart person.
Did you ask those people how to specify exactly
FROM <graphUri1>
FROM NAMED <graphUri2>
when the global unionDefaultGraph is set?
FROM and also including the union is a no-op anyway. It adds nothing as
the graph triples are already there
The unionDefaulGraph parameter should be treated as part of the query
semantics and you are simply overruling it with your implementation.
That there is a way to formulate the same semantics is irrelevant.
I think it is consistent - if you say what the default graph is in the
query, then it is that.
It adds
complexity when clients use FROM/FROM NAMED and defaultUnionGraph=true
Btw, the exact behavior of these clauses in the context of
defaultUnionGraph seems to be notably absent in the spec. That is too bad
The editor of this part of the SPARQL 1.0 spec created a careful balance
between different viewpoints. Having the default graph as the (fixed)
union was common but in many engines FROM* means nothing anyway. Other
people wanted web semantics (always read from the web). A third
community wanted "contexts". A fourth group wanted independent graphs.
All this switchable, namable union business is non-standard that's why
the URI of the union graph is <urn:x-arq:UnionGraph>.
What is relevant in the spec is that the dataset description is supposed
to be "complete".
So no FROM should mean empty graph regardless. That seemed unhelpful so
ARQ deviates.
But one FROM definitely does mean one graph.
Andy
There are bugs anyway - try asking for an explicitly named union with
the union flag on - it'll stackoverflow.
Simon
PS: my mail clients adds the sender automatically in cc. I agree that it
is annoying and will try to recall removing it, but at the same time, I
have had countless cases were you cc-ed me in exactly the same way.
Presumably because that's the way you send the email. "reply list" is
picking up cc's you included.
