Got bored by the relational database? Switch to a RDF store!

Got bored by the relational database? Switch to a RDF store! Fabrizio Giudici Tidalwave s.a.s.

Who I am ● Java consultant since 1996 ● Senior architect ● Java instructor for Sun since 1998 ● Member of the NetBeans Dream Team ● Technical Writer, Blogger at Java.Net, DZone ● http://weblogs.java.net/blog/fabriziogiudici/ ● http://www.tidalwave.it/people

Where I am using RDF stores http://bluemarine.tidalwave.it

Agenda ● Why the RDBMs? ● RDBMs issues ● The Semantic Model ● OpenSesame and Elmo ● A few code samples ● Conclusion

RDBMs are everywhere

What do we expect from a RDBM? ● Persistence ● Reliability ● Transactions ● Integrability ● Manageability

Lack of cohesion ● Do we really need a RDBM for those things? ● No, we don't – Persistence and transactions are good – The specific relational schema is evil ● RDBMs sell those stuff in a single package

ER-OO impedance ● Entity-Relationship is different than OO – Primary keys – No inheritance – No behaviour – Normalization rules – Relationship through external keys

ORMs ● Tools to minimize the ER-OO impedance ● Java has got a standard API: JPA – Hibernate, TopLink, EclipseLink, OpenJPA – Tries to abstract the database à la Java ● Good, but the RDBM has still to be designed ● And maintained

Can we get rid of the relational database?

The Semantic Model ● Semantic Technology != Semantic Web ● RDF: Resource Description Framework ● “Triples” are the atomic information item ● Subject / predicate / object – Java / is-a / programming-language – Fabrizio / is-member-of / NetBeans Dream Team – Verona / is-part-of / Veneto – Verona / has-plate / “VR”

The Semantic Model ● The subject is a resource ● The predicate is a property ● The object is a value ● A value is a resource or a primitive type ● Resources, properties identified by URL/URN – Just a naming scheme – Not necessarily web-related

Formal representation ● RDF is not related to XML ● XML is just one of the way to represent RDF – XML-RDF, unfortunately referred to as RDF ● Notation 3 (N3), another popular representation – Much more human-readable ● Other formats exist ● RDF representation is often referred to as “serialization”

(XML-)RDF is near to you ● RSS/RDF ● Dublin Core ● XMP by Adobe

Compared to RDBMs ● There's no fixed schema – Everything is a triple – “AAA slogan”: Anyone can say Anything about Any topic ● Adding new data types is adding triples – No need to add / alter tables – Maintainance is just updating data ● Databases can be distributed (federations) – Can be merged by just copying triples together

What about performance? ● Not as optimized as SQL ● There's no spread knowledge about tuning as for SQL ● Some missing parts – E.g. Sesame still misses select count(*)

OpenSesame, Elmo ● Popular Java infrastructure for RDF – FLOSS – http://www.openrdf.org ● Elmo providers JPA-like operations – Annotations – Specific API or even subset of JPA

A simple code example import org.openrdf.elmo.annotations.rdf; @rdf(GeoVocabulary.URI_GEO_LOCATION) public class GeoLocation { @rdf("http://www.w3.org/2003/01/geo/wgs84_pos#lat") private Double latitude; @rdf("http://www.w3.org/2003/01/geo/wgs84_pos#long") private Double longitude; @rdf("http://www.w3.org/2003/01/geo/wgs84_pos#alt") private Double altitude; @rdf("http://www.tidalwave.it/rdf/geo/2009/02/22#code") private String code; } ● Note the use of standard ontologies

A simple code example ● Declare persistent classes in META-INF/org.openrdf.elmo.concepts ● Choose a store – Memory – Memory backed by file – Database (transactional) Repository repository = new SailRepository( new MemoryStore(new File("/tmp/RDFStore"))); repository.initialize(); ElmoModule module = new ElmoModule(); SesameManagerFactory factory = new SesameManagerFactory(module, repository); SesameManager em = factory.createElmoManager();

Use as JPA EntityManager em.getTransaction().begin(); GeoLocation genova = new GeoLocation(); genova.setLatitude(45.0); genova.setLongitude(9.0); genova.setCode("GE"); em.persist(genova); em.getTransaction().commit();

Queries ● There are specific query languages ● SPARQL is one of the most popular ● Similar to SQL, but triples in place of tables PREFIX wgs84: <http://www.w3.org/2003/01/geo/wgs84_pos#> SELECT ?location WHERE { ?location wgs84:lat ?lat }

Running a query em.getTransaction().begin(); String queryString = "PREFIX wgs84: <http://www.w3.org/2003/01/geo/wgs84_pos#>n" + "SELECT ?location WHERE n" + " {n" + " ?location a ?type.n" + " ?location wgs84:lat ?latn" + " }"; final ElmoQuery query = em.createQuery(queryString). setType("type", GeoLocation.class). setParameter("lat", 45.0); final List<GeoLocation> result = query.getResultList(); for (GeoLocation l : result) { System.err.println(l); } em.getTransaction().commit();

Scratching the surface ● Elmo is powerful ● Supports advanced constructs – Objects with “multiple personality” – Mixins

Open issues ● OpenSesame doesn't support all databases ● Lack of experience – Programming skills – Maintainance – Tuning – Managerial culture ● Not widespread ● Performance?

Conclusion ● RDBMs are mainstream, but old ● They lead to rigid schemata, don't fit the OO ● It's possible to use something different ● RDF stores can be a viable alternative Fabrizio.Giudici@tidalwave.it

Got bored by the relational database? Switch to a RDF store!

by benfante on Oct 26, 2009

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Got bored by the relational database? Switch to a RDF store! — Presentation Transcript