Query operations are a key element in comunica for query evaluation. These operations are based on SPARQL Algebra, and use the TypeScript types provided by SPARQLAlgebra.js.
@comunica/bus-query-operation is the bus on which actors can subscribe to perform certain query operations.
@comunica/actor-query-operation-quadpattern is for instance responsible for evaluating quad patterns.
Operations take a certain operation as input, together with an optional context.
The output is a
BindingsStream, a set of variable names that occur in the bindings stream and optional metadata.
The input context and output metadata are optional hashes that can contain additional information that can help certain actors.
We describe all currently available context and metadata entries hereafter.
||A list of source objects and their type, e.g.
Currently supported types are
hypermedia (for TPF and similar variants),
hdt (for a local HDT file) and
file (for a local turtle file).
||The available Hydra search forms on a certain page.|
||An estimate of the total number of items in a collection.|