?P, ?O, ?G)True if an RDF triple <S,P,O>
exists, optionally in the graph G. The object O is
either a resource (atom) or one of the terms listed below. The described
types apply for the case where O is unbound. If O
is instantiated it is converted according to the rules described with rdf_assert/3.
Triples consist of the following three terms:
- Blank nodes are encoded by atoms that start with‘_:`.
- IRIs appear in two notations:
- Full IRIs are encoded by atoms that do not start with‘_:`.
Specifically, an IRI term is not required to follow the IRI standard
- Abbreviated IRI notation that allows IRI prefix aliases that are
registered by rdf_register_prefix/[2,3] to be used. Their notation is
where Alias and Local are atoms. Each abbreviated IRI is expanded by the
system to a full IRI.
- Literals appear in two notations:
- String @ Lang
- A language-tagged string, where String is a Prolog string and Lang
is an atom.
- A type qualified literal. For unknown types, Value is a
Prolog string. If type is known, the Prolog representations from the
table below are used.
|Datatype IRI ||Prolog term |
|xsd:decimal||float (1) |
|XSD integer sub-types||integer |
(1) The current implementation of
xsd:decimal values as
floats is formally incorrect. Future versions of SWI-Prolog may
introduce decimal as a subtype of rational.
(2) SS fields denote the number of seconds. This can
either be an integer or a float.
date_time structure can have a 7th field that
denotes the timezone offset in seconds as an integer.
In addition, a ground object value is translated into a
properly typed RDF literal using rdf_canonical_literal/2.
There is a fine distinction in how duplicate statements are handled
in rdf/[3,4]: backtracking over rdf/3
will never return duplicate triples that appear in multiple graphs. rdf/4
will return such duplicate triples, because their graph term differs.
|S ||is the subject term. It is either a blank
node or IRI. |
|P ||is the predicate term. It is always an
|O ||is the object term. It is either a
literal, a blank node or IRI (except for |
that denote the values of datatype XSD boolean).
|G ||is the graph term. It is always an IRI. |
?Predicate, ?Object)Elementary query for triples. Subject and Predicate
are atoms representing the fully qualified URL of the resource. Object
is either an atom representing a resource or
- See also
- - Triple
- xsd_number_string/2 and xsd_time_string/3
are used to convert between lexical representations and Prolog terms.
if the object is a literal value. If a value of the form
NameSpaceID:LocalName is provided it is expanded to a ground atom using expand_goal/2.
This implies you can use this construct in compiled code without paying
a performance penalty. Literal values take one of the following forms:
- If the value is a simple atom it is the textual representation of a
string literal without explicit type or language qualifier.
- lang(LangID, Atom)
- Atom represents the text of a string literal qualified with
the given language.
- type(TypeID, Value)
- Used for attributes qualified using the
TypeID. The Value is either the textual
representation or a natural Prolog representation. See the option
convert_typed_literal(:Convertor) of the parser. The storage layer
provides efficient handling of atoms, integers (64-bit) and floats
(native C-doubles). All other data is represented as a Prolog record.
For literal querying purposes, Object can be of the form
literal(+Query, -Value), where Query is one of the terms
below. If the Query takes a literal argument and the value has a numeric
type numerical comparison is performed.
- Perform exact match and demand the language or type qualifiers to match.
This query is fully indexed.
- Perform a full but case-insensitive match. This query is fully indexed.
- Same as
icase(Text). Backward compatibility.
- Match any literal that contains Text as a case-insensitive
substring. The query is not indexed on Object.
- Match any literal that contains Text delimited by a non
alpha-numeric character, the start or end of the string. The query is
not indexed on Object.
- Match any literal that starts with Text. This call is
intended for completion. The query is indexed using the skip list of
- Match any literal that is equal or larger than Literal in the
ordered set of literals.
- Match any literal that is larger than Literal in the ordered
set of literals.
- Match any literal that is equal to Literal in the ordered set
- Match any literal that is equal or smaller than Literal in
the ordered set of literals.
- Match any literal that is smaller than Literal in the ordered
set of literals.
- between(+Literal1, +Literal2)
- Match any literal that is between Literal1 and Literal2
in the ordered set of literals. This may include both Literal1
- Match any literal that matches Pattern case insensitively,
where the‘*' character in Pattern matches zero or more
Backtracking never returns duplicate triples. Duplicates can be
retrieved using rdf/4. The predicate rdf/3
raises a type-error if called with improper arguments. If rdf/3
is called with a term
literal(_) as Subject or Predicate
object it fails silently. This allows for graph matching goals like
rdf(O,P2,O2) to proceed without