On 04/02/11 23:04, Tim Harsch wrote:
I noticed some code in Fuseki that will throw error if a query
contains FROM/FROM NAMED clauses. I think it makes sense given it is
Sparql 1.1 SOH protocol and since you specify the dataset in your
call you can't do it in the FROM/FROM NAMED clauses too. But, does
that mean that Fuseki will never deprecate Joseki since in order to
query multiple data sets you would need FROM/FROM NAMED clauses in
the query and only Joseki would support that? Or will/does Fuseki
support standard Sparql endpoint semantics as well?
Fuseki provides the ability to publish and update datasets on the web.
Mostly it's one dataset (and the current command line only handled one
dataset but internally it looks up any incoming request and directs it
to the right dataset).
That's one feature Joseki currently has that Fuseki has not expose. Yet.
The reason you get an error if you use FROM/FROM NAMED is because it's
publishing a dataset. Normally FROM/FROM NAMED means load (using HTTP
GET) the graphs named, create a dataset and query it. That's what the
/sparql service (joseki:ProcessorSPARQL) does. It offers a general
purpose query service, which is not offering query over a dataset but
enables the loading of graphs into a dataset. Some people use
sparql.org/sparql for this - not that I can guarantee it's up and
running.
Fuseki is running like joseki:ProcessorSPARQL_FixedDS. This standard
SPARQl behaviour - in fact, most other systems only offer this behaviour
because they provide access to the data stored behind them.
It can be a bit expensive and opens up certain issues of reducing
service to other datasets by hitting the server with work to load data.
By the way, Joseki has a built in 50K triple limit on any data it
loads to reduce accidents. There's no reason why another service
couldn't be added to Fuseki to do that.
GRAPH is the SPARQL keyword to pick one graph in the dataset.
It would be possible to enable the other behaviour of FROM/FROM NAMED
for TDB:
http://openjena.org/wiki/TDB/DynamicDatasets
which is useful for the effect of default graph (select a few from many,
merge and query, except it does not actually merge the data) and GRAPH ?g.
And you can do the FROM/FROM NAMED thing with the ARQ command line tools.
Andy
