Oracle 10g Release 2 / Oracle 11g offers a robust, scalable, secure platform to store RDF and OWL data. It allows efficient storage, loading and querying of semantic data. Queries are enhanced by adding relationships (ontologies) to data and evaluated on the basis of semantics. Data storage is in the form of RDF triples (Subject, Predicate, Object) and can scale up to millions of triples. The triples stored in the semantic data store are modeled as a graphed structure. All the data is stored in a single central schema allowing access to users for loading and querying data.
The Subject and Object are modeled as nodes, while the predicates are denoted by links in the graphed structure. Nodes are stored and efficiently reused when required. An RDF triple in the semantic store has a subject (start node), predicate (relationship), object (end node), which comprises a link. A new link is created on inserting a new triple and nodes are reused if similar nodes already exists.
New object types are defined to manage Semantic Data viz. SDO_RDF_TRIPLE and SDO_RDF_TRIPLE_S. The former stores the references to the data and the latter holds the actual data content. The nodes (Subject, Object) are stored in the RDF_NODE$ table, which can be further broken down into START_NODE_ID and END_NODE_ID. The RDF_LINKS$ table stores the record for the link whenever a new triple is inserted. Blank nodes may also be inserted as a part of any triple, which are stored in the RDF_BLANK_NODE$. An RDF model stores references to all the RDF data in the database and can be created by executing the sem_apis.create_sem_model procedure.
Get started with semantic data management on Windows XP and configure semantic web technology support in Oracle 11g Release 1.
This article gives an overview of semantic data storage, however to get additional in-depth information on Semantic Data support in Oracle, here are some useful links:
References: RDF support in Oracle (.pdf)
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