SHACL Portal

Introduction

This topic contains a kind of portal to the contents of the W3C Recommendation "Shapes Constraint Language (SHACL)". This is still Work In Progress.

Disclaimer

In cases where the texts in this topic would contradict the contents of the W3C Recommendation "Shapes Constraint Language (SHACL)" the latter prevails.

Terms and Definitions

NOTE - Links in the text first go to the short descriptions below, and from there to the SHACL Recommendation.

SHACL Processor - A SHACL validation engine that takes as input a graph to be validated (called data graph) and a graph containing SHACL shapes declarations (called shapes graph), and produces a validation report, also expressed as a graph.The data graphs and shapes graphs may be merged in one file.

Data Graph - your RDF data-to-be-validated in Turtle, JSON-LD or RDF/XML

Nodes - The set of nodes of an RDF graph is the set of subjects and objects of triples in the graph.

Shapes Graph - a graph that contains two main types of shapes: node shapes and property shapes

Node Shape - declares constraints directly on a node. A node shape usually contains several property shapes which are declared through the sh:property predicate.

Property shape - declares a constraint on the value associated with a node through a path; a property shape has a property sh:path that declares the path that goes from the focus node to the value that they describe. The most frequent paths are predicate paths which are formed by a single IRI.

Property Paths

Property Path - A possible route through a graph between two graph nodes. A trivial case is a property path of length exactly 1, which is a triple pattern. The ends of the path may be RDF terms or variables. Variables can not be used as part of the path itself, only the ends.

sh:path - A property shape is the subject of a triple that has sh:path as its predicate. A shape has at most one value for sh:path. Each value of sh:path in a shape must be a well-formed SHACL property path.

elt - A path element ('elt' = element), which may itself be composed of path constructs.

sh:PredicatePath - A subject-to-object path with a length of one and an IRI as object
sh:InversePath - An object-to-subject path
sh:SequencePath - A path that is a sequence of elt1 followed by elt2 ; a SHACL list with at least two members and each member is a well-formed SHACL property path.
sh:AlternativePath - A path that entails an alternative of elt1 or elt2 (all possibilities are tried)
sh:ZeroOrMorePath - A path that connects the subject and object of the path by zero or more matches of elt
sh:OneOrMorePath - A path that connects the subject and object of the path by one or more matches of elt
sh:ZeroOrOnePath - A path that connects the subject and object of the path by zero or one matches of elt

RDF term - IRI, literal, or blank node

Value Node - defined as follows:

For node shapes the value nodes are the individual focus nodes, forming a set with exactly one member.
For property shapes with a value for sh:path p the value nodes are the set of nodes in the data graph that can be reached from the focus node with the path mapping of p.Unless stated otherwise, the value of sh:resultPath of each validation result is a SHACL property path that represents an equivalent path to the one provided in the shape.

Shape - A collection of targets and contraints,

Target Declarations

Focus Node - Any targeted rdfs:subject or rdfs:object in the Data Graph
Targets - define which nodes in the data graph must conform to the shape;
sh:targetClass - targets all resources that are instances of a given class;
sh:targetNode - targets a specific resource, e.g., a given instance;
sh:targetSubjectsOf - targets all the subjects of a given predicate;
sh:targetObjectsOf - targets all the objects of a given predicate

SHACL Constraint Components

Constraint - defines how to validate a node;

Type	Constraints	Definition
Cardinality	sh:minCount	Cardinality that restricts the minimun amount of occurences of a given property. Default value: 0
Cardinality	sh:maxCount	Cardinality that restricts the maximum amount of occurences of a given property. Default value: 0
Types of values	sh:class	Constraint that restricts to nodes that are instances of a given class
	sh:datatype	Constraint that restricts the xsd: datatype of all value nodes to a given value
	sh:nodeKind	Constraint that restricts the kind of value of a property to one of the following: BlankNode, IRI, Literal, BlankNodeOrIRI, BlankdNodeOrLiteral, or IRIOrLiteral
Other constraints	sh:in	Enumerates the value options that a property may have
Other constraints	sh:hasValue	Verifies whether the focus node has a given value
Range of values	sh:minInclusive	The minimum inclusive value of a value range
	sh:maxInclusive	The maximum inclusive value of a value range
	sh:minExclusive	The minimum exclusive value of a value range
	sh:maxExclusive	The maximum exclusive value of a value range
String based	sh:minLength	Restricts the minimum string length on value nodes
	sh:maxLength	Restricts the maximum string length on value nodes
	sh:pattern	Checks if the string value matches a regular expression
	sh:languageIn	Checks that the property values are expressed in the given list of languages
	sh:uniqueLang	Checks that no pair of nodes use the same language tag
Logical constraints	sh:not	Negation of a shape
	sh:and	Conjunction of a list of shapes
	sh:or	Each node conforms to at least one of the provided shapes or both
	sh:xone	Specifies a condition that each value node conforms to exactly one of the provided shapes (not both) - (a.k.a. XOR - eXclusive OR)
Closed shapes	sh:closed	If set to true, properties that are not explicitly described in the shape are not allowed
Closed shapes	sh:ignoredProperties	Optional list of properties that are also permitted in addition to those explicitly enumerated in the shape
Property pair constraints	sh:equals	The sets of values of both properties at a given focus node must be equal
	sh:disjoint	The sets of values of both properties at a given focus node must be different
	sh:lessThan	The values must be smaller than the values of another property
	sh:lessThanOrEquals	The values must be smaller or equal than the values of another property
Qualified shapes	sh:node	All values of a given property must comply with a given shape
	sh:property	Can be used to specify that each value node has a given property shape
	sh:qualifiedValueShape	The shape that the specified number of nodes needs to conform to
	sh:qualifiedValueShapesDisjoint	If set to true, for the counting, the nodes must not conform to any of the sibling shapes
	sh:qualifiedMinCount	Minimum number of nodes that conform to the shape
	sh:qualifiedMaxCount	Maximum number of nodes that conform to the shape

Shape Characteristics

Type	Constraints	Definition
Non-validating characteristic	sh:name	Provide human-readable labels for a property
	sh:description	Provide a description of a property
	sh:group	Group several constraints together
	sh:order	Relative order of the property
	sh:defaultValue	Define the default value of a given shape

Prefix Declarations for SPARQL Queries

Term	Desription
sh:declare	The values of the property sh:declare are IRIs or blank nodes, and these values are called prefix declarations.
sh:prefix	Prefix declarations have exactly one value for the property sh:prefix. The values of sh:prefix are literals of datatype xsd:string. Prefix declarations have exactly one value for the property
sh:prefixes	The union of all individual prefix mappings that are values of the SPARQL property path sh:prefixes/owl:imports*/sh:declare of the SPARQL-based constraint or validator.
sh:namespace	The values of sh:namespace are literals of datatype xsd:anyURI; Each value of sh:namespace is turned into the IRIREF in the PREFIX declaration
sh:select	A SHACL processor transforms the values of sh:select into SPARQL by prepending PREFIX declarations for all prefix mappings.
sh:ask	A SHACL processor transforms the values of sh:ask into SPARQL by prepending PREFIX declarations for all prefix mappings.

SPARQL-based Constraint Components

Term	Desription
sh:sparql	A SPARQL-based constraint declaring the SPARQL query to evaluate
sh:parameter	The values of sh:parameter are called parameter declarations. Each parameter declaration has exactly one value for the property sh:path. At parameter declarations, the value of sh:path is an IRI.
sh:labelTemplate	Can be used at any constraint component to suggest how constraints could be rendered to humans.
sh:nodeValidator	A sh:SPARQLSelectValidator for node shapes
sh:propertyValidator	A sh:SPARQLSelectValidator for property shapes
sh:validator	A sh:SPARQLAskValidator

Validation results vocabulary

Term	Desription
sh:ValidationReport	Result of the validation process that reports the conformance and the set of all validation results
sh:conforms	True if a focus node conforms with a given shape and false otherwise
sh:result	Contains the result graph for each validation result
sh:shapesGraphWellFormed	Informs the consumer of the validation report about the fact that the validated shapes graph is well-formed.
sh:ValidationResult	Used to report individual SHACL validation results
sh:focusNode	The node which was tested and caused the validation result
sh:resultPath	Points to a well-formed SHACL property path
sh:value	Points to the value of the property that caused the result
sh:sourceShape	Points to the shape that the given focus node was validated against
sh:sourceConstraintComponent	Refers to which constraint component has been violated
sh:detail	May point to further details about the cause of the violation
sh:resultMessage	Textual details about the error. The message can be affected by the sh:message property in the shapes graph
sh:resultSeverity	A value which is equal to the sh:severity value of the shape that caused the violation error. The default value is sh:Violation