Triples

Reference: 4.2 Syntax for Triple Patterns

The fundamental building block of RDF and SPARQL is the triple, a tuple consisting of a subject, predicate, and object. In Flint, there are two ways to write a series of triples.

The first is as a vector of three-element vectors. For example, the triples in the :where clause here are represented as vectors:

{:prefixes {:foaf "<http://xmlns.com/foaf/0.1/>"}
 :select   [?name ?age]
 :where    [[?x :foaf/name ?name]
            [?x :foaf/age ?age]]}

which after SPARQL translation becomes:

PREFIX foaf:<http://xmlns.com/foaf/0.1/>
SELECT ?name ?age
WHERE {
    ?x foaf:name ?name .
    ?x foaf:age ?age .
}

The other way to write a triple block in Flint is the normal form of the IGraph protocol. Each normal form map associates subjects with predicate-object maps, and each predicate-object map associates predicates with object sets. The example:

{:prefixes {:foaf "<http://xmlns.com/foaf/0.1/>"}
 :select   [?name ?age]
 :where    [{?x {:foaf/name #{?name}
                 :foaf/age  #{?age}}}]}

becomes:

WHERE {
    ?x foaf:name ?name ;
       foaf:age  ?age .
}

Note that only when triples written as normal form maps in Flint will they share subjects in the SPARQL representation. Since objects are represented as sets, a similar grouping occurs if more than one object exists in a set:

{:prefixes {:foaf "<http://xmlns.com/foaf/0.1/>"}
 :select   [?y]
 :where    [{?y {:foaf/givenName #{"Ymir", "_Ymir"}}}]}

which becomes

PREFIX foaf:<http://xmlns.com/foaf/0.1/>
SELECT ?y
WHERE {
    ?y foaf:givenName "Ymir" , "_Ymir"
}

which is the same as

PREFIX foaf:<http://xmlns.com/foaf/0.1/>
SELECT ?y
WHERE {
    ?y foaf:givenName "Ymir" .
    ?y foaf:givenName "_Ymir" .
}

Both forms can be combined to form a graph pattern:

{:prefixes {:foaf "<http://xmlns.com/foaf/0.1/>"
            :dc   "<http://purl.org/dc/elements/1.1/>"}
 :select   [?name ?age ?title]
 :where    [{?x {:foaf/name #{?name}
                 :foaf/age  #{?age}}}
            [?y :dc/creator ?name]
            [?y :dc/title ?title]]}

which become:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX dc:   <http://purl.org/dc/elements/1.1/>
SELECT ?name ?age ?title
WHERE {
    ?x foaf:name ?name ;
       foaf:age ?age .
    ?y dc:creator ?name .
    ?y dc:title ?title .
}

Restrictions

Subjects can be one of the following:

• Variables
• IRIs or prefixed IRIs
• Blank nodes

Predicates can be one of the following:

• Variables
• IRIs or prefixed IRIs
• :a/a
• Property paths

Objects can be one of the following:

• Variables
• IRIs or prefixed IRIs
• Blank nodes
• Literals

NOTE: Property paths are not allowed in triples in CONSTRUCT clauses, nor in DELETE and INSERT DATA clauses.

NOTE: Blank nodes are not allowed in triples in DELETE clauses (including DELETE WHERE and DELETE DATA).

NOTE: Variables are not allowed in triples in DELETE DATA OR INSERT DATA clauses.

NOTE: Technically literals are allowed in subject position according to the SPARQL spec, but no RDF implementation accepts that, so Flint does not allow for subject literals either.

NOTE: SPARQL has syntactic sugar for easy writing of RDF lists, but for simplicity that is not implemented in Flint.

Property Paths

Reference: 9. Property Paths

Property paths act as syntactic sugar for predicate sequences in RDF graphs. A property path in Flint is an IRI (including :a) or a list of the form (op path ...); this is similar to Clojure functions or Flint expressions. The following is a table of path operations:

Flint	SPARQL form	Arglist
alt	(path \| path \| ...)	[& paths]
cat	(path / path / ...)	[& paths]
inv	^(path)	[path]
?	(path)?	[path]
*	(path)*	[path]
+	(path)+	[path]
not	!(neg-path)	[neg-path]

A neg-path is a subset of paths that can only include alt operations or IRIs. No other operations are allowed, even as args to alt ops.

An example of a query with a simple property path:

{:prefixes {:foaf "<http://xmlns.com/foaf/0.1/>"}
 :select   [?friendName]
 :where    [{?x {:foaf/name #{"Eren Jaeger"}
                (cat (* :foaf/knows) :foaf/name) #{?friendName}}}]}

becomes:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT ?friendName
WHERE {
    ?x foaf:name "Eren Jaeger" ;
       (foaf:knows* / foaf:name) ?friendName .
}

NOTE: Variables are not allowed in property paths.