SHACL to SPARQL Conversion#
BuildingMOTIF uses SHACL shapes to ensure that a metadata model contains the required metadata to support a given set of applications. SHACL validation only yields whether or not a given node in the model passes or fails validation. To aid in the execution of applications dependent on a SHACL shape, BuildingMOTIF provides functionality to extract from the model the nodes/edges that were used to validate the shape.
See Generating SPARQL Queries for how to use the shape_to_query function. This page gives an overview of the algorithm.
Shape-to-query Algorithm#
The main method, shape_to_query, takes a SHACL shape represented as a URI and generates a SPARQL query to select information from an RDF graph that satisfies the constraints defined by the SHACL shape.
At a high level, the method works by first transforming the SHACL shape into a set of WHERE clauses, and then assembling these clauses into a complete SPARQL query.
The shape-to-query algorithm takes as input a definition of a SHACL Node Shape.
SELECT clause generation#
The SELECT clause of the resulting SPARQL query is generated as follows.
Each query has at least a ?target variable in the generated SELECT clause.
This variable represents a target node of the SHACL shape.
The algorithm adds one variable to the SELECT clause for each Property Shape associated
with the Node Shape through sh:property.
The variable name is pulled from a sh:name annotation on the Property Shape if one exists;
otherwise, it is assigned a generated variable name.
If a UNION clause exists within the SPARQL query, the algorithm generates variable names independently for each branch of the UNION clause.
The resulting SELECT clause contains the union of the different sets of variable names.
WHERE clause generation#
The WHERE clause of the resulting SPARQL query is generated from each of the Property Shapes associated with the input Node Shape, and a few annotations directly on the NodeShape.
The Node Shape target definition is converted to a SPARQL query clause as follows:
Target Definition |
Query Pattern |
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Additionally, any sh:class <c> constraint on the Node Shape is also transformed into ?target rdf:type/rdfs:subClassOf* <c>.
Except for sh:targetNode, if more than one of the target clauses exists (e.g., sh:targetClass brick:VAV, brick:RVAV) then the algorithm uses a UNION clause to combine the independent query patterns.
The algorithm currently interprets a set of Property Shape-based constraint components into SPARQL query patterns. At this stage, only the following clauses are supported:
Property Shape pattern |
SPARQL query pattern |
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