SHACL Specification Draft

Holger KnublauchW3C RDF Data Shapes Meeting

2015-05-19

History Lesson: Protégé-2000• Frame-based, closed-world modeling tool• Declarative core language, extended by• Protégé Axiom Language (PAL)

Source: http://protege.stanford.edu/plugins/paltabs/pal-quickguide/PALTutorial.pdf

Where did PAL go?

• Lack of Standardization• Lack of support outside of academia• Wave of Open-World RDFS/OWL enthusiasm

• Fundamentally different situation with SPARQL• SHACL can stand on the shoulders of giants

SHACL Draft Status

• This draft includes contributions from almost everyone in the WG

• Covers all approved requirements• Prototype (Open Source Jena API & TBC Free)

could be made available anytime• TopQuadrant’s interests align with community• Able to evolve quickly, willing to listen

Basic Principles

• Simple, declarative vocabulary for common cases (“Core” or “Lite”)

• Fully integrated mechanism for complex cases– SPARQL, but adding JavaScript etc is easy

• Macro facility to make complex cases simple• Core language itself is defined as Macros• Very consistent design, easy to implement• Designed for both the Web and Intranets

Vocabulary

• Focus node: currently validated RDF node• Constraint: condition that can be validated,

producing errors or warnings• Shape: collection of constraints about the

same focus node• Template: reusable constraint wrapped into

new high-level vocabulary term

ex:ExampleConstraintViolation a sh:Error ; sh:root ex:MyCurrentNode ; sh:subject ex:MyCurrentNode ; sh:predicate ex:someProperty ; sh:object ex:someInvalidValue ; sh:message "Incorrect value: expected something else" .

Constraint Violationssh:ConstraintViolation

sh:message : xsd:stringsh:root : rdfs:Resource

sh:subject : rdfs:Resourcesh:predicate : rdf:Propertysh:object

sh:detail

sh:Warning sh:Error

sh:FatalError

sh:Constraintsh:source

User Story 1s1:PropertyMustHaveDomainShape a sh:Shape ; rdfs:comment "Every rdf:Property must have at least one rdfs:domain statement." ; sh:scopeClass rdf:Property ; sh:property [ sh:predicate rdfs:domain ; sh:minCount 1 ; ] .

User Story 2s2:PersonShape a sh:Shape ; rdfs:comment "Persons must have at least one name (xsd:string)." ; sh:scopeClass s2:Person ; sh:property [ sh:predicate s2:name ; sh:datatype xsd:string ; sh:minCount 1 ; ] .

User Story 2 (with ShapeClass)s2b:Person a sh:ShapeClass ; rdfs:label "Person" ; sh:property [ sh:predicate s2b:name ; sh:datatype xsd:string ; sh:minCount 1 ; rdfs:comment "Persons must have at least one name (xsd:string)." ; ] .

{ "@id" : "s2b:Person", "@type" : "sh:ShapeClass", "label" : "Person", "property" : { "predicate" : "s2b:name", "datatype" : "xsd:string", "minCount" : 1, "comment" : "Persons must have at least one name (xsd:string)." }}

Turtle

JSON-LD

User Story 3s3:PersonMarriageShape a sh:Shape ; sh:scopeClass s3:Person ; sh:constraint [ sh:message "Same-sex marriage is not permitted (in this model) – spouse is {?gender}." ; sh:predicate s3:spouse ; sh:severity sh:Warning ; sh:sparql """ SELECT ?this (?this AS ?subject) (?spouse AS ?object) ?gender WHERE { ?this s3:gender ?gender . ?this s3:spouse ?spouse . ?spouse s3:gender ?gender . }""" ; ] .

User Story 4 (1/4)

• Issue tracker with context-specific constraints• Issues may be assigned, unassigned, resolved– Resolved issues must not have assignedTo– The submitter of unresolved issues must have

email address• Also: IssueShape is closed, i.e. only the three

enumerated properties are permitted

User Story 4 (2/4)s4:IssueShape a sh:Shape ; sh:constraint sh:ClosedShape ; sh:scopeClass s4:Issue ; sh:property [ sh:predicate s4:assignedTo ; sh:valueType s4:Person ; ] ; sh:property [ sh:predicate s4:status ; sh:maxCount 1 ; sh:minCount 1 ; sh:valueType s4:Status ; ] ; sh:property [ sh:predicate s4:submittedBy ; sh:valueType s4:Person ; ] .

s4:PendingIssueShape a sh:Shape ; rdfs:comment "Shape for Issues that are not resolved yet." ; sh:scopeClass s4:Issue ; sh:scopeShape [ sh:property [ sh:predicate s4:status ; sh:allowedValues ( s4:assigned s4:unassigned ) ; sh:minCount 1 ; ] ; ] ; sh:property [ rdfs:comment "Pending issues must be submitted by someone who has an email address." ; sh:predicate s4:submittedBy ; sh:valueShape [ sh:property [ sh:predicate s4:email ; sh:minCount 1 ; ] ; ] ; ] .

User Story 4 (3/4)

Scope for which this shape applies

s4:ResolvedIssueShape a sh:Shape ; rdfs:comment "Shape for Issues that are resolved." ; sh:scopeClass s4:Issue ; sh:scopeShape [ sh:property [ sh:predicate s4:status ; sh:hasValue s4:resolved ; ] ; ] ; sh:property [ sh:predicate s4:assignedTo ; rdfs:comment "Resolved issues must not be assigned to anyone." ; sh:maxCount 0 ; ] .

User Story 4 (4/4)

Scope for which this shape applies

OrConstraint Example from EDMore:Aggregation sh:constraint [ a sh:OrConstraint ; rdfs:comment "#7 edm:aggregatedCHO, edm:isShownAt or edm:isShownBy must be present" ; sh:shapes ( [ sh:property [ sh:predicate edm:aggregatedCHO ; sh:minCount 1 ; ] ; ] [ sh:property [ sh:predicate edm:isShownAt ; sh:minCount 1 ; ] ; ] [ sh:property [ sh:predicate edm:isShownBy ; sh:minCount 1 ; ] ; ] ) ; ] .

ore:Aggregation sh:constraint [ sh:sparql """ SELECT ?this WHERE { FILTER NOT EXISTS { ?this edm:aggregatedCHO | edm:isShownAt | edm:isShownBy ?any } } """ ; ]

User Story 21s21:UniqueLanguagePropertyConstraint a sh:ConstraintTemplate ; rdfs:label "Unique language property constraint" ; rdfs:subClassOf sh:AbstractPropertyConstraint ; sh:message "Language {?lang} is used more than once for {?predicate}" ; sh:sparql """ SELECT ?this (lang(?label1) AS ?lang) (?this AS ?subject) ?predicate (?label1 AS ?object) WHERE { ?this ?predicate ?label1 . ?this ?predicate ?label2 . FILTER ((lang(?label1) = lang(?label2)) && (?label1 != ?label2)) . }""" .

Reusable constraint macro

s21:SKOSConceptShape a sh:Shape ; sh:scopeClass skos:Concept ; sh:constraint [ a s21:UniqueLanguagePropertyConstraint ; sh:predicate skos:prefLabel ; ] .

User Story 23 (1/3)s23:FlightReservationShape a sh:Shape ; sh:scopeClass schema:FlightReservation ; sh:property [ sh:predicate schema:reservationFor ; sh:valueShape [ sh:constraint [ sh:message "A future date is required to show a boarding pass." sh:predicate schema:departureTime ; sh:sparql """ SELECT ?this (?this AS ?subject) (?t AS ?object) WHERE { ?this schema:departureTime ?t . FILTER (?t <= NOW()) }""" ; ] ; ] ; ] .

User Story 23 (2/3)s23:IrreflexiveChildrenShape a sh:Shape ; sh:scopeClass schema:Person ; sh:property [ a s23:IrreflexivePropertyConstraint ; sh:predicate schema:children ; sh:valueType schema:Person ; ] .

s23:IrreflexivePropertyConstraint a sh:ConstraintTemplate ; rdfs:subClassOf sh:PropertyConstraint ; rdfs:comment "Detects triples where ?this points to itself." ; sh:message "For {?predicate} a focus not cannot point to itself." ; sh:sparql """ SELECT ?this (?this AS ?subject) ?predicate (?this AS ?object) WHERE { ?this ?predicate ?this }""" .

s23:MrSelfie a schema:Person ; schema:children s23:MrSelfie .

User Story 23 (3/3)

s23:OrderedPropertyPairConstraint a sh:ConstraintTemplate ; rdfs:subClassOf sh:TemplateConstraint ; sh:argument [ rdfs:label "The property with the smaller values." ; sh:predicate s23:property1 ; sh:valueType rdf:Property ; ] ; sh:argument [ rdfs:label "The property with the larger values." ; sh:predicate s23:property2 ; sh:valueType rdf:Property ; ] ; sh:message "{?property1} cannot be larger than {?property2}" ; sh:sparql """ SELECT ?this (?this AS ?subject) (?property1 AS ?predicate) (?value1 AS ?object) ?property1 ?property2 WHERE { ?this ?property1 ?value1 . ?this ?property2 ?value2 . FILTER (?value1 > ?value2) }""" .

s23:MsImpossible a schema:Person ; schema:birthDate "2015-05-10"^^xsd:date ; schema:deathDate "2015-05-09"^^xsd:date .

s23:BirthAndDeathDateShape a sh:Shape ; sh:scopeClass schema:Person ; sh:constraint [ a s23:OrderedPropertyPairConstraint ; s23:property1 schema:birthDate ; s23:property2 schema:deathDate ; ] .

Same for start & end date and other pairs

Reuse of Templates for EDMrda:Person a sh:ShapeClass ; sh:constraint [ a edmsh:OrderedPropertyPairConstraint ; edmsh:property1 rdaGr2:dateOfBirth ; edmsh:property2 rdaGr2:dateOfDeath ; rdfs:comment "#4 rdaGr2:dateofBirth must be earlier than rdaGr2:dateOfDeath and rdaGr2:dateOfDeath must be later than rdaGr2:dateofBirth (DC:R-43) (W3:R-6.6) (W3:R-5.9.1)" ; ] .

rdfs:Resource sh:constraint [ a edmsh:LanguageShouldBePresentPropertyConstraint ; sh:predicate skos:prefLabel ; rdfs:comment "#5 Ideally the language tag should be present for skos:prefLabel" ; ] ; sh:constraint [ a edmsh:UniqueLanguagePropertyConstraint ; sh:predicate skos:prefLabel ; rdfs:comment "#5 We must have only one skos:prefLabel per language." ; ] .

SHACL Design Axis• Pragmatic design for real-world problems• Based on many years of industry experience• Trade-off between declarative and expressive• Half of the examples needed SPARQL• Declarative sub-languages can have

non-SPARQL implementations

Declarativeness Expressiveness

SPARQL JavaScriptSHACL Core Other SHACL Templates

Popular Templates evolve into Standards

The Current Drafthttp://w3c.github.io/data-shapes/shacl/

Elements of the Draft

• Self-contained, consistent document• “Core” and “Advanced” parts• Plenty of examples (we can wait with Primer)• Open Issues/TODOs are clearly marked• Includes SHACL system vocabulary in Turtle• SHACL is defined in itself

SHACL Metamodel

sh:Shape rdfs:Class

sh:ShapeClass

sh:scopeClass

sh:scopeShape

rdfs:Resourcerdf:typesh:nodeShape

sh:Shape

sh:Constraint

sh:PropertyConstraintsh:minCount : xsd:integersh:maxCount : xsd:integersh:defaultValuesh:allowedValues : rdf:List sh:hasValuesh:datatype : rdfs:Datatypesh:nodeKind : sh:NodeKindsh:valueType : rdfs:Classsh:valueShape : sh:Shape

sh:AbstractPropertyConstraint

sh:predicate : rdf:Propertyrdfs:label : xsd:stringrdfs:comment : xsd:string

sh:InversePropertyConstraint

sh:minCount : xsd:integersh:maxCount : xsd:integersh:valueType : rdfs:Class

… ?

sh:constraint

sh:inverseProperty

sh:property

sh:TemplateConstraintsh:NativeConstraint

sh:sparql : xsd:string

Example Definition (sh:hasValue)

A Future-Proof SHACL• Most W3C languages were not really designed for

the Web, have hard-coded syntax and semantics• Templates: new high-level language elements• Functions: SPARQL extensions– Some with SPARQL bodies– Some with other executable languages (JS etc)– Some provided by custom extensions (e.g. GeoSPARQL)

• Directly benefits from SPARQL’s evolution,new SPARQL end points, database features etc

• Open to future developments (JSON-LD etc)• sh:rule could be added consistently