On 10/09/13 17:57, "Dr. André Lanka" wrote:
Hi Andy,
thank you very much. I saw the example earlier but missed that it
perfectly matches my needs. *facepalm*
In general the approach works really fine. Yet, TDBGraphAssembler seems
to ignore the transaction framework. All is ok when I use the assembler
at the beginning of the code. But when I used the original datasets
transactional before, I get a TDBTransactionException (see below for
more details)
The call correctly reuses the underlying and already created dataset
graph (what is really great for us) but there seems to be no possibility
to force a transaction start.
Is this intended for some reason?
When you select individual graphs, there is no transaction control.
Transactions are per-dataset (the journal is per database).
Cross-database transactions would need either distribute transactions
(e.g. e.g. XA transactions) or multi-dataset logging.
Having all graphs in one DB is more usual.
You should be able to operate directly on the dataset the graph is in
transactionally, with care, if you ensure the system is MRSW (Multiple
reader OR Single Writer).
Andy
André
Code that fails:
ds1 = TDBFactory.createDataset(new Location("/var/tmp/namedTest1"));
ds1.begin(ReadWrite.READ);
ds1.end();
build = (Dataset) AssemblerUtils.build("/var/tmp/tdbNew.ttl",
"http://jena.hpl.hp.com/2005/11/Assembler#RDFDataset";);
StackTrace:
...
Caused by: com.hp.hpl.jena.tdb.transaction.TDBTransactionException: Not
in a transaction
at
com.hp.hpl.jena.tdb.transaction.DatasetGraphTransaction.get(DatasetGraphTransaction.java:104)
at
com.hp.hpl.jena.tdb.transaction.DatasetGraphTransaction.get(DatasetGraphTransaction.java:1)
at
com.hp.hpl.jena.sparql.core.DatasetGraphTrackActive.getDefaultGraph(DatasetGraphTrackActive.java:99)
at
com.hp.hpl.jena.sparql.core.DatasetImpl.getDefaultModel(DatasetImpl.java:103)
at
com.hp.hpl.jena.tdb.assembler.TDBGraphAssembler.open(TDBGraphAssembler.java:95)
at
com.hp.hpl.jena.tdb.assembler.TDBGraphAssembler.open(TDBGraphAssembler.java:1)
at
com.hp.hpl.jena.assembler.assemblers.AssemblerGroup$PlainAssemblerGroup.openBySpecificType(AssemblerGroup.java:130)
... 39 more
Turtle Definition:
@prefix tdb: <http://jena.hpl.hp.com/2008/tdb#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix ja: <http://jena.hpl.hp.com/2005/11/Assembler#> .
[] ja:loadClass "com.hp.hpl.jena.tdb.TDB" .
tdb:DatasetTDB rdfs:subClassOf ja:RDFDataset .
tdb:GraphTDB rdfs:subClassOf ja:Model .
# A dataset of one TDB-backed graph as the default graph and
# an in-memory graph as a named graph.
<#dataset> rdf:type ja:RDFDataset ;
ja:defaultGraph <#graph> ;
ja:namedGraph
[ ja:graphName <http://example.org/name1> ;
ja:graph <#graph2> ] ;
.
<#graph> rdf:type tdb:GraphTDB ;
tdb:location "/var/tmp/namedTest1" ;
.
<#graph2> rdf:type tdb:GraphTDB ;
tdb:location "/var/tmp/namedTest2" ;
On 10.09.2013 12:30, Andy Seaborne wrote:
Hello Jena community,
I'm looking for a possibility to SPARQL two different TDB backed
datasets within one query. The background is that I have a few TDB
stores (say A and B) and one special TDB store S containing a few
triples that I want to "share" with the other stores.
For instance I want to do something like this:
SELECT ?o WHERE { GRAPH <S> { ?s ?p ?o. } GRAPH <A> { ?s1 ?p1 ?o.} }
In addition, S needs to be writeable and the changes need to be promptly
visible for other queries. Even if I change A to B in the above example.
I know about named graphs but unfortunately they are no option in our
scenario. Could I do it by using assemblers? Or is there any other
possibility?
We use the current versions of Jena/ARQ/TDB in pure Java.
You can create a single dataset with graphs from different storages, the
your queries will look exactly as in your example.
This can be done in an assembler or in code.
Example:
http://jena.apache.org/documentation/tdb/assembler.html#mixed-datasets
Andy
