Hi Hendrik
I second that; And I also add that sometimes stuff should not be joined at
all, but resolved in two different queries. I know, D2R isn't suited for
connecting at two databases at once, but if it could tell when to JOIN,
when to use the same FROM and when to join things from memory, it would be
great.
Cheers,
--
diogo patrão
On Wed, Apr 3, 2013 at 10:17 PM, Hendrik Adler <hen.ad...@gmail.com> wrote:
> Hi,
>
> I am new to this forum and run into a problem. I would like to map a rdf
> schema to a view in a PostgreSQL-database.
> Problem is that the query that d2rq generates is extremely slow.
>
> This is the sparql-query:
> select ?time ?value where
> {
> ?a <uri:sensor:value> ?value.
> ?a <uri:sensor:timestamp> ?time.
> FILTER (?time < '2012-01-06T08:00:00'^^xsd:dateTime && ?time >
> '2012-01-06T00:00:00'^^xsd:dateTime) }
>
> And this the generated SQL Code:
> DISTINCT SELECT ...... FROM "v1" AS "T1_v1", "v1" AS "T2_v1" WHERE (....)
>
> FROM "v1" AS "T1_v1", "v1" AS "T2_v1" leads to a really bad performance,
> because PostgreSQL joins view v1 with itself by nesting loops.
> I think it happens because the view generates the measured values from a
> denormalized table, where 3600 values are stored per one column using
> arrays.
> (for better performance and saving storage space)
>
>
> That is why it would great to have a simple query in the form:
> DISTINCT SELECT ...... FROM "v1" WHERE (....)
>
> Is there a way to use just one Table after the "from" to avoid selfjoins
> or must I adapt the code? I start the server (version 0.8.1) with the
> "fast" option.
>
> Many Thanks
> Hendrik
>
> That is my ttl-config:
>
> # D2RQ Namespace
> @prefix d2rq: <http://www.wiwiss.fu-berlin.de/suhl/bizer/D2RQ/0.1#>
> .
> # Namespace of the ontology
> @prefix : <uri:sensor:measure> .
> #@prefix : <:measurement> .
> # Namespace of the mapping file; does not appear in mapped data
> @prefix map: <file:///Users/d2r/example.ttl#> .
>
>
> # Other namespaces
> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
> @prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
> @prefix jdbc: <http://d2rq.org/terms/jdbc/> .
> @prefix sens: <urn:measurement:> .
>
> @prefix db: <> .
> @prefix vocab: <vocab/> .
> @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
>
> map:Configuration a d2rq:Configuration;
> d2rq:useAllOptimizations true.
>
> map:database a d2rq:Database;
> d2rq:jdbcDSN "jdbc:postgresql://192.168.0.181/measured-data";
> d2rq:jdbcDriver "org.postgresql.Driver";
> d2rq:username "abc";
> d2rq:password "123";
> jdbc:autoReconnect "true";
> jdbc:zeroDateTimeBehavior "convertToNull";
> .
>
> # Table measuredvalues
> map:measuredvalues a d2rq:ClassMap;
> d2rq:dataStorage map:database;
> d2rq:class :measuredvalues;
> d2rq:uriPattern "
> http://example.org/lineItems/sensorid@@v1.sensorid@@-@@v1.timestamp@@";;
> .
>
> map:measuredvaluetimestamp a d2rq:PropertyBridge;
> d2rq:belongsToClassMap map:measuredvalues;
> d2rq:column "v1.timestamp";
> d2rq:datatype xsd:dateTime;
> d2rq:property :timestamp;
> .
>
> map:measuredvalue_2_value a d2rq:PropertyBridge;
> d2rq:belongsToClassMap map:measuredvalues;
> d2rq:column "v1.value";
> d2rq:datatype xsd:double;
> d2rq:property :value;
> .
>
> map:measuredvaluesensorid a d2rq:PropertyBridge;
> d2rq:belongsToClassMap map:measuredvalues;
> d2rq:column "v1.sensorid";
> d2rq:datatype xsd:integer;
> d2rq:property :sensorid;
> .
>
>
>
>
>
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