Loading and Inferencing

Loading Data into RDF Server #

SemSpect is a Snapshot Explorer #

SemSpect is a snapshot RDF data explorer and querying tool. This means that SemSpect does not fetch data from a SPARQL endpoint on demand, but loads the specified list of RDF input data for which it generates special indices. If the input data changes, the index must also be recalculated.

RDF SemSpect indices are managed by derivo SemStore, a proprietary in-memory RDF store. SemStore uses low-memory index structures that have been specially developed and optimized for the efficient processing of SemSpect front-end requests. Parts of these index structures are based on a variant of the Bitmap Triple (BT) indices, which extend the compact triple data structure of the RDF compression format HDT.

Since the SemStore indices for a given set of RDF datasets are persisted on disk, the initialization of SemSpect is much faster at each subsequent startup. Whether a persistent index already exists for a particular input is decided by checking for each of the supplied input files whether it has changed (modified date and time of the file system) since the index was created.

How is RDF data interpreted in SemSpect? #

SemSpect is a RDF data explorer rather than a RDF schema explorer. The provided RDF schema is used to distinguish RDF classes from resources and properties between resources resp. between a resource and a literal. If the schema part is missing or ambiguous, SemSpect tries to assume a schema that is as plausible as possible using heuristics. As a guide, SemSpect proceeds as follows:

  • all resources from the namespaces rdf:, rdfs:, owl:, swrl:, and xsd: (such as owl:Class) are not considered as explorable resources

  • all properties from the namespaces rdf:, rdfs:, owl: (such as rdf:type, rdfs:subPropertyOf) are not considered for exploration

  • SemSpect converts RDF collections (rdf:List, rdf:Seq, rdf:Bag, rdf:Alt) into human-readable sequence values that are displayed alongside usual data and annotation property assertions

  • SemSpect will processes annotations on property assertions which have been reified according to RDF/OWL or specified in the Turtle-star format and shows them in the tabular view of resources or property assertions

Supported Inference #

SemSpect applies basic inference including:

  • RDFS (rdfs:domain, rdfs:range, rdfs:subClassOf, rdfs:subPropertyOf)
  • owl:equivalentProperty, owl:inverseOf, owl:SymmetricProperty

This means that the logical consequences of these axioms are computed and written into the SemStore indices at load time. When exploring a dataset in SemSpect, you will see the supplied input data enriched with the results of these derivations.