Query Operations
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.
Context Entries
Name | Related Actors | Description |
---|---|---|
sources |
@comunica/actor-rdf-resolve-quad-pattern-qpf |
A list of source objects and their type, e.g. { type: 'hypermedia', value: 'http://fragments.dbpedia.org/2016-04/en'} |
Currently supported types are sparql
, hypermedia
(for TPF and similar variants), hdt
(for a local HDT file) and file
(for a local turtle file).
Metadata Entries
Name | Related Actors | Description |
---|---|---|
searchForms |
@comunica/actor-rdf-resolve-quad-pattern-qpf , @comunica/actor-rdf-metadata-extract-hydra-controls |
The available Hydra search forms on a certain page. |
totalItems |
@comunica/actor-rdf-resolve-quad-pattern-qpf , @comunica/actor-rdf-metadata-extract-hydra-count |
An estimate of the total number of items in a collection. |