Triple Patterns¶

Triple patterns are the fundamental building blocks of SPARQL queries. They match subject-predicate-object triples in RDF data.

Basic Triple Pattern¶

A triple pattern consists of three components:

?subject ?predicate ?object

Each component can be: - A variable (starts with ? or $) - An IRI (in angle brackets or prefixed) - A literal (for objects only)

Variables¶

Variables bind to values in matched triples:

# All three positions as variables
SELECT ?s ?p ?o
WHERE { ?s ?p ?o }

# Mix of variables and constants
SELECT ?name
WHERE { <http://example.org/alice> <http://xmlns.com/foaf/0.1/name> ?name }

IRIs (Resources)¶

IRIs identify resources:

# Full IRI
SELECT ?name
WHERE { <http://example.org/alice> <http://xmlns.com/foaf/0.1/name> ?name }

# Prefixed IRI
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX ex: <http://example.org/>

SELECT ?name
WHERE { ex:alice foaf:name ?name }

Literals¶

Literals represent data values:

# Plain literal
SELECT ?person
WHERE { ?person foaf:name "Alice" }

# Language-tagged literal
SELECT ?label
WHERE { ?x rdfs:label ?label FILTER(LANG(?label) = "en") }

# Typed literal
SELECT ?person
WHERE { ?person foaf:age "30"^^xsd:integer }

OPTIONAL Patterns¶

Match patterns that may or may not exist:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name ?email
WHERE {
    ?person foaf:name ?name .
    OPTIONAL { ?person foaf:mbox ?email }
}

Results include people without email addresses (with ?email unbound).

UNION Patterns¶

Match alternative patterns:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name
WHERE {
    { ?person foaf:name ?name }
    UNION
    { ?person foaf:nick ?name }
}

MINUS Patterns¶

Exclude matching patterns:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

# Find people who don't know Bob
SELECT ?name
WHERE {
    ?person foaf:name ?name
    MINUS {
        ?person foaf:knows <http://example.org/bob>
    }
}

Graph Patterns¶

Query specific named graphs:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

# Query a specific graph
SELECT ?name
WHERE {
    GRAPH <http://example.org/friends> {
        ?person foaf:name ?name
    }
}

# Query with graph variable
SELECT ?g ?name
WHERE {
    GRAPH ?g {
        ?person foaf:name ?name
    }
}

Nested Patterns¶

Combine patterns with grouping:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name ?friend
WHERE {
    ?person foaf:name ?name .
    {
        ?person foaf:knows ?f .
        ?f foaf:name ?friend
    }
}

BIND¶

Create new bindings from expressions:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name ?upperName
WHERE {
    ?person foaf:name ?name
    BIND(UCASE(?name) AS ?upperName)
}

VALUES¶

Provide inline data:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name ?email
WHERE {
    VALUES ?person { <http://example.org/alice> <http://example.org/bob> }
    ?person foaf:name ?name .
    OPTIONAL { ?person foaf:mbox ?email }
}

Subqueries¶

Nest queries within patterns:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name ?maxAge
WHERE {
    ?person foaf:name ?name .
    {
        SELECT (MAX(?age) AS ?maxAge)
        WHERE {
            ?p foaf:age ?age
        }
    }
}

Pattern Summary¶

Pattern	Description
`?s ?p ?o`	Basic triple pattern
`OPTIONAL { }`	Optional match
`{ } UNION { }`	Alternative patterns
`MINUS { }`	Negation
`GRAPH ?g { }`	Named graph
`BIND(expr AS ?var)`	Variable binding
`VALUES ?var { }`	Inline data
`{ SELECT ... }`	Subquery