10 RDF Views: Relational Data as RDF

You can create and use RDF views over relational data in RDF Graph.

Relational data is viewed as virtual RDF triples using one of the two forms of RDB2RDF mapping described in W3C documents on Direct Mapping and R2RML mapping:

• R2RML: RDB to RDF Mapping Language, W3C Recommendation (http://www.w3.org/TR/r2rml/)

• A Direct Mapping of Relational Data to RDF, W3C Recommendation (http://www.w3.org/TR/rdb-direct-mapping/)

Note:

If you are using RDF Graph Server and Query UI application, then you can easily create an RDF view using the RDF View Wizard. You can also run SPARQL queries on the RDF view and visualize the query output. See RDF Views from Relational Data for more information.

This chapter explains the following topics:

• Why Use RDF Views on Relational Data?
  Using RDF views on relational data enables you to query relational data using SPARQL and integrate data available from different sources.
• API Support for RDF Views
  Subprograms are included in the SEM_APIS package for creating, dropping, and exporting (that is, materializing the content of) RDF views.
• Example: Using an RDF View Graph with Direct Mapping
  This section shows an example of using an RDF view graph with direct mapping.
• Combining Native RDF Data with Virtual RDB2RDF Data
  You can combine native triple data with virtual RDB2RDF triple data (from an RDF view graph) in a single SEM_MATCH query by means of the SERVICE keyword.