The Virtuoso Sponger is the Linked Data middleware component of
Virtuoso that generates Linked Data from a variety of data sources,
supporting a wide variety of data representation and serialization
formats. The sponger is transparently integrated into Virtuoso's
SPARQL Query Processor where it delivers URI de-referencing within
SPARQL query patterns, across disparate data spaces. It also
delivers configurable smart HTTP caching services. Optionally, it
can be used by the Virtuoso Content
Crawler to periodically populate and replenish data within the
native RDF Quad Store.
The sponger is a fully fledged HTTP proxy service that is also
directly accessible via SOAP or REST interfaces.
As depicted below, OpenLink's broad portfolio of
Linked-Data-aware products supports a number of routes for creating
or consuming Linked Data. The Sponger provides a key platform for
developers to generate quality data meshes from unstructured or
semi-structured data sources.
Figure 16.96. OpenLink Linked
Data generation options
Architecturally, the Sponger is comprised of a number of
Cartridges two types of cartridges: Extractor and Meta Cartridges.
Extractor Cartridges focus on data extraction and transformation
services while the Meta Cartridges provide lookups and joins across
other linked data spaces and Web 2.0 APIs. Both cartridge types are
themselves comprised of a data extractors and RDF Schema/Ontology
Cartridges are is highly customizable. Custom cartridges can be
developed using any language supported by the Virtuoso Server
Extensions API enabling structured linked data generation from
resource types not available in the default Sponger Cartridge
collection bundled -- as part of the Virtuoso Cartridges VAD package .
Figure 16.97. Virtuoso metadata
extraction & RDF structured data generation