The Virtuoso Sponger ("Sponger") is an RDF middleware layer (built into Virtuoso's SPARQL Processor, Web Content Crawler, and WebDAV RDF Sink Folder) that produces RDF instance data from non-RDF Data Sources (i.e., an RDFizer).
The Sponger is comprised of Cartridges that host Ontology Mappers and Metadata Extractors. The Ontology Mappers cover a wide range of shared ontologies, while the Metadata Extractors cover a wide range of (X)HTML, XML, XML Web Services, and Binary Files.
The production of RDF from RDF follows the sequence below:
- Metadata Extractor extracts metadata from data source (e.g., a web resource)
- Extracted Metadata is processed using one or more Ontology Mappers to produce RDF instance Data