RE: Introducing myself - SOA organised with RDF

Hi

>It is important to bear in mind that its best to think of RDF in terms
>of its abstract syntax, i.e. a graph of nodes, rather than the RDF/XML
>concrete syntax.  There are a number of systems around that will store
>significant numbers of RDF triples in a relational store.  We do one,
>Jena (http://jena.sourceforge.net) and there are others - sesame,
>mulgari, redland, etc.  I'd strongly suggest you take a look at these,
>or, if you really feel an XML database is the way to go - I'd like to
>understand why

Based on your recommendation I decided to give Jena a go. We installed a
Postgres on the Linux box we're using for persistence, and we've been able
to load up our database and make SPARQL queries on the graph. 

However my initial experiences with the response time of these SPARQL
queries is not all that convincing. It seems that using the Java API is very
fast, but has the drawback that it requires the queries to be
pre-programmed. That may be fine for specific types of standard requests,
but for the ability to quickly build and execute more tailormade requests we
really need to be able to use SPARQL. 

My test case is to make a SPARQL expression for immediate graph vicinity to
a specific node - an operation that is a must for jumping from node to node
through a graphical RDF-viewer like Welkin. This operation can be performed
in 10-15 seconds on my eXist XML database. The SPARQL-query I made for Jena
took 75 sec. to execute on the very same set of data. (This of course could
be because I am still a wannabe SPARQL programmer.)

So my question is: Is this an inherent problem of executing SPARQL, or do I
have look out for specific properties of the query complexity when I design
my queries. 

Here's another question: Is it at all possible using SPARQL to define a
query that will return a graph containing all nodes by forward-chaining from
a specific start node? It seems to me that SPARQL is similar to SQL in that
it does not have a "memory", that will enable me to remember visited nodes
in a graph. Also I am not aware of any recursive features I can use in my
queries. Or do I just need to go back and read some more?.....
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Received on Wednesday, 21 November 2007 22:18:29 UTC