a ; "

Triple Patterns

\n\n

Definition: Triple PatternA triple pattern is member of the set:

\n (RDF-T ∪ V) x (I ∪ V) x (RDF-T ∪ V)

\n

This definition of Triple Pattern includes literal subjects. This has been noted by RDF-core.

\n
\"[The RDF core Working Group] noted that it is aware of no reason why literals should\nnot be subjects and a future WG with a less restrictive charter may\nextend the syntaxes to allow literals as the subjects of statements.\"\n
\n

Because RDF graphs may not contain literal subjects, any SPARQL triple pattern with a literal as subject will fail to match on any RDF graph.

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Query Variables

\n\n

Definition: Query VariableA query variable is a member of the set V where V is infinite and disjoint from RDF-T.

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18.1.10 SPARQL Query

\n\n

Definition: SPARQL QueryA SPARQL Abstract Query is a tuple (E, DS, QF) where:

\n\n

Definition: Query LevelA query level is a graph pattern, a set of group and aggregation, and a set of solution modifiers.

\n

A query is a tree of \"query levels\", where each subquery forms one query level in the tree.

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Solution Mapping

\n\n

A solution mapping is a mapping from a set of variables to a set of RDF terms. We use the term 'solution' where it is clear.

\n

Definition: Solution MappingA solution mapping, μ, is a partial function μ : V -> RDF-T.

\n

The domain of μ, dom(μ), is the subset of V where μ is defined.

\n

Definition: Solution SequenceA solution sequence is a list of solutions, possibly unordered.

\n

Write expr(μ) for the value of the expression expr, using the terms for variables given by μ. Evaluation may result in an error.

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Basic Graph Patterns

\n\n

Definition: Basic Graph PatternA Basic Graph Pattern is a set of Triple Patterns.

\n

The empty graph pattern is a basic graph pattern which is the empty set.

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RDF Dataset

\n\n

Definition: RDF DatasetAn RDF dataset is a set:

\n { G, (<u1>, G1), (<u2>, G2), . . . (<un>, Gn) }

\n where G and each Gi are graphs, and each <ui> is an IRI. Each <ui> is distinct.

\n

G is called the default graph. (<ui>, Gi) are called named graphs.

\n

Definition: Active GraphThe active graph is the graph from the dataset used for basic graph pattern matching.

\n

Definition: RDF Dataset Merge

\n

Let DS1 = { G1, (<u11>, G11), (<u12>, G12), . . . (<u1n>, G1n) },

\n and DS2 = { G2, (<u21>, G21), (<u22>, G22), . . . (<u2m>, G2m) }

\n

then we define the RDF Dataset Merge of DS1 and DS2 to be:

\n DS={ G, (<u1>, G1), (<u2>, G2), . . . (<uk>, Gk) }

\n where:

\n

Write N1 for { <u1j> j = 1 to n }

\n Write N2 for { <u2j> j = 1 to m }

\n
    \n
  • G is the merge of G1 and G2
    • \n
  • (<ui>, Gi) where <ui> is in N1 but not in N2
    • \n
  • (<ui>, Gi) where <ui> is in N2 but not in N1
    • \n
  • (<ui>, Gi) where <ui> is equal to <uj> in N1 and equal to <uk> in N2 and Gi is the merge of G1j and G2k
    • \n
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RDF Terms

\n\n

SPARQL is defined in terms of IRIs [Internationalized Resource Identifiers (IRIs)]. IRIs are a subset of RDF URI References that omits the use of spaces.

\n

Definition: RDF TermLet I be the set of all IRIs.

\n Let RDF-L be the set of all RDF Literals

\n Let RDF-B be the set of all blank nodes in RDF graphs

\n

The set of RDF Terms , RDF-T, is I ∪ RDF-L ∪ RDF-B.

\n

This definition of RDF Term collects together several basic notions from the RDF data model, but updated to refer to IRIs rather than RDF URI references.

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Simple Literal

\n\n

Definition: Simple Literal

\n

The set of Simple Literals is the set of all RDF Literals with no language tag or datatype IRI.

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Property Path Patterns

\n\n

Definition: Property PathA Property Path is a sequence of triples, ti in sequence ST, with n = length(ST)-1, such that, for i=0 to n, the object of ti is the same term as the subject of ti+1.

\n

We call the subject of t0 the start of the path.

\n

We call the object of tn the end of the path.

\n

A Property Path is a path in graph G if each ti is a triple of G.

\n

A property path does not span multiple graphs in a dataset.

\n

Definition: Property Path ExpressionA property path expression is an expression using the property path forms described above .

\n

Definition: Property Path PatternLet PP be the set of all property path expressions. A property path pattern is a member of the set:

\n (RDF-T ∪ V) x PP x (RDF-T ∪ V)

\n

A Property Path Pattern is a generalization of a Triple Pattern to include a property path expression in the property position.

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Initial Definitions

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Solution Sequence Modifiers

\n\n

Definition: Solution Sequence ModifierA solution sequence modifier is one of:

\n
    \n
  • Order By modifier: put the solutions in order
    • \n
  • Projection modifier: choose certain variables
    • \n
  • Distinct modifier: ensure solutions in the sequence are unique
    • \n
  • Reduced modifier: permit any non-distinct solutions to be eliminated
    • \n
  • Offset modifier: control where the solutions start from in the overall sequence of solutions
    • \n
  • Limit modifier: restrict the number of solutions
    • \n
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