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Re: Introducing myself - SOA organised with RDF

From: Ignazio Palmisano <ignazio.palmisano@googlemail.com>
Date: Thu, 22 Nov 2007 11:42:37 +0000
Message-ID: <6a61afdc0711220342q5bf7cb12ge9260fcd66e3e979@mail.gmail.com>
To: semantic-web@w3.org
2007/11/21, Frank Carvalho <dko4342@vip.cybercity.dk>:
>
>
>
> 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?.....



If I got your point, you want ways to hop from a node to another node in the
proximity, say A is your node, you want node B such that:
A someproperty B

In this case it may be faster to use the Jena API instead of SPARQL: once
you get A in some way, you call A.listProperties() to have all statements
with A as subject (including those referring to B). More specialized
requests, such as list the properties with a specific predicate, are easy as
well.
HTh,
I.


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Received on Friday, 23 November 2007 12:20:33 UTC

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