SHACL Skill

Design, implement, and validate RDF data structures with the Shapes Constraint Language. This skill embodies the practical wisdom that shapes provide a fundamentally different way of thinking about data than classes—they describe structural expectations and patterns without requiring formal hierarchies.

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Core Philosophy (Cagle's Principles)

"OWL is not going away, but there is definitely a shift occurring within the semantic community around the use of SHAPES, rather than classes and properties."

Key Insights:

1. Shapes, not classes: "A shape is, at its core, simply a pattern that is common to one or more nodes in a graph"
2. SHACL wraps SPARQL: "Learn SPARQL. SHACL can be thought of as a dedicated wrapper around SPARQL queries and filters"
3. Validation, not inference: SHACL validates existing data; OWL prevents invalid data through inference
4. Beyond validation: SHACL provides "structural information, including data groupings, ordering, and interfaces"
5. The future is shapes: "SHACL will eventually be foundational not just for RDF, but at the broader level of data design and management"

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Guide Router

Load only ONE guide per request:

User Intent	Load Guide	Content
Node shapes, targeting, focus nodes	02-NODE-SHAPES.md	NodeShape fundamentals
Property shapes, paths, constraints	03-PROPERTY-SHAPES.md	PropertyShape patterns
Constraint types, cardinality, datatype	04-CONSTRAINT-COMPONENTS.md	All constraint components
Property paths, traversal, sequences	05-PROPERTY-PATHS.md	SHACL path expressions
Targets, class targets, SPARQL targets	06-TARGETS.md	Focus node selection
Validation reports, results, severity	07-VALIDATION-REPORTS.md	Report structure
SPARQL constraints, custom validation	08-SHACL-SPARQL.md	Advanced constraints
AI/LLM integration, query generation	09-SHACL-FOR-AI.md	SHACL with AI systems
UI generation, forms, DASH widgets	10-SHACL-UI.md	Interface scaffolding
Taxonomies, SKOS, classification	11-SHACL-TAXONOMIES.md	Taxonomy validation
Best practices, patterns, anti-patterns	12-BEST-PRACTICES.md	Design guidance

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SHACL vs OWL: The Paradigm Shift

Why the Shift?

"Reasoners are disappearing from newer knowledge graph systems, partly because there is no real demand and partly because SPARQL and SPARQL Update are more targeted in their capabilities." — Cagle

Aspect	OWL	SHACL
Purpose	Inference & classification	Validation & constraints
Approach	Forward-chaining rules	SPARQL-based checking
Invalid data	Prevents storage	Allows storage, reports issues
Severity	Binary (valid/invalid)	Graduated (Violation/Warning/Info)
World assumption	Open (unknown ≠ false)	Closed by default
Implementation	Requires reasoner	SPARQL engine sufficient
Learning curve	Steep (formal logic)	Accessible (structural)

Philosophical Differences

OWL (Open World):

# No children stated doesn't mean childless
ex:John a ex:Person .
# John might have children we don't know about
# OWL CANNOT conclude John is childless

SHACL (Closed World by Default):

ex:PersonShape a sh:NodeShape ;
    sh:targetClass ex:Person ;
    sh:property [
        sh:path ex:hasChild ;
        sh:maxCount 0 ;
        sh:message "Person has no children recorded"
    ] .
# SHACL CAN validate that John has no children in the data

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SHACL Quick Reference

Core Vocabulary

@prefix sh: <http://www.w3.org/ns/shacl#> .
@prefix ex: <http://example.org/> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .

Basic Node Shape

ex:PersonShape a sh:NodeShape ;
    sh:targetClass ex:Person ;           # What to validate
    sh:property ex:NamePropertyShape ;   # Property constraints
    sh:property ex:EmailPropertyShape .

Basic Property Shape

ex:NamePropertyShape a sh:PropertyShape ;
    sh:path ex:name ;                    # Property to constrain
    sh:minCount 1 ;                      # At least one
    sh:maxCount 1 ;                      # At most one
    sh:datatype xsd:string ;             # Must be string
    sh:message "Person must have exactly one name" .

Inline Property Shapes

ex:PersonShape a sh:NodeShape ;
    sh:targetClass ex:Person ;
    sh:property [
        sh:path ex:name ;
        sh:minCount 1 ;
        sh:datatype xsd:string
    ] ;
    sh:property [
        sh:path ex:email ;
        sh:pattern "^[^@]+@[^@]+\\.[^@]+$" ;
        sh:severity sh:Warning
    ] .

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Constraint Components Summary

Value Type Constraints

Constraint	Purpose	Example
sh:class	Instance of class	sh:class ex:Person
sh:datatype	Literal datatype	sh:datatype xsd:string
sh:nodeKind	IRI/Literal/BlankNode	sh:nodeKind sh:IRI

Cardinality Constraints

Constraint	Purpose	Example
sh:minCount	Minimum values	sh:minCount 1
sh:maxCount	Maximum values	sh:maxCount 1

Value Range Constraints

Constraint	Purpose	Example
sh:minInclusive	>= value	sh:minInclusive 0
sh:maxInclusive	<= value	sh:maxInclusive 150
sh:minExclusive	> value	sh:minExclusive 0
sh:maxExclusive	< value	sh:maxExclusive 200

String Constraints

Constraint	Purpose	Example
sh:minLength	Min string length	sh:minLength 1
sh:maxLength	Max string length	sh:maxLength 100
sh:pattern	Regex match	sh:pattern "^[A-Z]"
sh:languageIn	Allowed languages	sh:languageIn ("en" "de")
sh:uniqueLang	One per language	sh:uniqueLang true

Value Constraints

Constraint	Purpose	Example
sh:in	Enumeration	sh:in ("draft" "published")
sh:hasValue	Required value	sh:hasValue ex:Required

Logical Constraints

Constraint	Purpose	Example
sh:and	All must validate	sh:and (ex:Shape1 ex:Shape2)
sh:or	One must validate	sh:or (ex:TypeA ex:TypeB)
sh:not	Must NOT validate	sh:not ex:DraftShape
sh:xone	Exactly one validates	sh:xone (ex:A ex:B)

Shape-Based Constraints

Constraint	Purpose	Example
sh:node	Value conforms to shape	sh:node ex:AddressShape
sh:property	Property constraint	sh:property [...]
sh:qualifiedValueShape	Qualified cardinality	See guide

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Property Paths

SHACL supports SPARQL-style property paths:

# Predicate path (direct property)
sh:path ex:name

# Sequence path (chain of properties)
sh:path (ex:parent ex:name)

# Alternative path
sh:path [sh:alternativePath (rdfs:label skos:prefLabel)]

# Inverse path
sh:path [sh:inversePath ex:parent]

# Zero or more
sh:path [sh:zeroOrMorePath ex:parent]

# One or more
sh:path [sh:oneOrMorePath ex:parent]

# Zero or one
sh:path [sh:zeroOrOnePath ex:middleName]

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Target Types

Class-Based Targets

ex:PersonShape a sh:NodeShape ;
    sh:targetClass ex:Person .

Node Targets

ex:SpecificShape a sh:NodeShape ;
    sh:targetNode ex:ImportantResource .

Property-Based Targets

# Subjects of property
ex:AuthorShape a sh:NodeShape ;
    sh:targetSubjectsOf ex:wrote .

# Objects of property
ex:BookShape a sh:NodeShape ;
    sh:targetObjectsOf ex:wrote .

Implicit Class Targets

# Shape that is also a class
ex:Person a sh:NodeShape, rdfs:Class ;
    sh:property [...] .

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Severity Levels

sh:Violation  # Critical failure (default)
sh:Warning    # Non-critical alert
sh:Info       # Informational message

Usage:

ex:EmailShape a sh:PropertyShape ;
    sh:path ex:email ;
    sh:pattern "^[^@]+@[^@]+$" ;
    sh:severity sh:Warning ;
    sh:message "Email format appears invalid" .

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Complete Example

@prefix sh: <http://www.w3.org/ns/shacl#> .
@prefix ex: <http://example.org/> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .

ex:EmployeeShape a sh:NodeShape ;
    sh:targetClass ex:Employee ;

    # Required employee ID
    sh:property [
        sh:path ex:employeeId ;
        sh:name "employeeId" ;
        sh:description "Unique employee identifier" ;
        sh:minCount 1 ;
        sh:maxCount 1 ;
        sh:datatype xsd:string ;
        sh:pattern "^EMP[0-9]{6}$" ;
        sh:severity sh:Violation ;
        sh:message "Employee must have exactly one valid ID (format: EMP######)"
    ] ;

    # Required organization
    sh:property [
        sh:path ex:worksFor ;
        sh:name "worksFor" ;
        sh:minCount 1 ;
        sh:class ex:Organization ;
        sh:severity sh:Violation ;
        sh:message "Employee must work for at least one organization"
    ] ;

    # Optional manager (at most one)
    sh:property [
        sh:path ex:hasManager ;
        sh:name "manager" ;
        sh:maxCount 1 ;
        sh:class ex:Employee ;
        sh:severity sh:Warning ;
        sh:message "Employee should have at most one manager"
    ] .

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SHACL Use Cases (Cagle's Framework)

1. Data Quality Assurance: Validate data pipelines before storage
2. Classification: Categorize unstructured data into shapes
3. Structural Definition: Define expected data entry structures
4. Functional Metadata: Bridge object-oriented and graph systems
5. UI Generation: Generate forms and interfaces from shapes
6. API Contracts: Define request/response structures
7. AI Integration: Describe query parameters for LLMs
8. Documentation: Self-documenting requirements specifications

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Resources

W3C Specifications

• SHACL Core
• SHACL Advanced Features
• SHACL Use Cases and Requirements

Books

• Semantic Web for the Working Ontologist by Allemang, Hendler, Gandon (3rd ed.)
• Learning SPARQL by Bob DuCharme (O'Reilly)

Kurt Cagle's Work

• The Ontologist — Substack newsletter
• The Cagle Report — Enterprise data and AI
• Validating ANYTHING With SHACL
• SHACL and Taxonomies
• SHACL for User Interfaces
• Using SHACL and AI for Creating Queries