- From: Ignazio Palmisano <ignazio.palmisano@googlemail.com>
- Date: Thu, 22 Nov 2007 11:42:37 +0000
- To: semantic-web@w3.org
- Message-ID: <6a61afdc0711220342q5bf7cb12ge9260fcd66e3e979@mail.gmail.com>
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. -- > View this message in context: > http://www.nabble.com/Introducing-myself---SOA-organised-with-RDF-tf4263503.html#a13887039 > Sent from the w3.org - semantic-web mailing list archive at Nabble.com. > > >
Received on Friday, 23 November 2007 12:20:33 UTC