NAME

Attean::API::Model - RDF Model

VERSION

This document describes Attean::API::Model version 0.034

DESCRIPTION

The Attean::API::Model role defines a common API for all RDF models to conform to. It is provides a consistent interface for probing, counting, and retrieving Attean::API::Quads matching a pattern, as well as related functionality such as enumerating the graph names, and extracting structured data from the models' quads.

REQUIRED METHODS

The following methods are required by the Attean::API::Model role:

get_quads( $subject, $predicate, $object, $graph )

Returns an Attean::API::Iterator for quads in the model that match the supplied $subject, $predicate, $object, and $graph.

Any of these terms may be:

* An Attean::API::Term object, in which case matching is equality-based

* A Attean::API::Variable object or undef, in which case that term will be considered as a wildcard for the purposes of matching

* An ARRAY reference of Attean::API::Term objects, in which case the matching will be equality-based on the disjunction of the supplied terms

The returned iterator conforms to both Attean::API::Iterator and Attean::API::QuadIterator.

count_quads( $subject, $predicate, $object, $graph )

Returns the number of quads in the model matching the supplied pattern (using the same matching semantics as get_quads).

count_quads_estimate( $subject, $predicate, $object, $graph )

Returns an estimate of the number of quads in the model matching the supplied pattern (using the same matching semantics as get_quads). This estimate is guaranteed to non-zero if the count returned from an equivalent call to `count_quads` would return a non-zero result.

get_graphs

Returns an Attean::API::Iterator of distinct Attean::API::Term objects that are used in the graph position of quads in the model.

METHODS

The Attean::API::Model role provides default implementations of the following methods:

get_bindings( $subject, $predicate, $object, $graph )

Returns an Attean::API::Iterator of Attean::API::Result objects corresponding to quads in the model matching the supplied pattern. For each Attean::API::Variable in the pattern list, a mapping will be present in the corresponding result object. For example, $model->get_bindings( variable('s') ) will return an iterator of results containing just a mapping from 's' to subjects of all quads in the model.

get_list( $graph, $head )

Returns an Attean::API::Iterator of Attean::API::Term objects that are members of the rdf:List with the specified $head (and matching restricted to only the specified $graph).

To check if a certain term is a list, the holds method may be used, for example:

$model->holds($head, iri('http://www.w3.org/1999/02/22-rdf-syntax-ns#first'), undef, $graph))

will return true if a given term $head is a list.

get_sequence( $graph, $head )

Returns an Attean::API::Iterator of Attean::API::Term objects that are members of the rdf:Sequence with the specified $head (and matching restricted to only the specified $graph).

subjects( $predicate, $object, $graph )

Returns an Attean::API::Iterator of Attean::API::Term objects of all subjects of quads matching the supplied pattern (using the same matching semantics as get_quads).

The objects returned will not necessarily be unique. It will instead be equivalent to calling get_quads and accessing $quad->subject for each $quad value returned by the iterator. For an iterator of unique subjects, use $model->subjects->uniq.

predicates( $subject, $object, $graph )

Returns an Attean::API::Iterator of Attean::API::Term objects of all predicates of quads matching the supplied pattern (using the same matching semantics as get_quads with an undef predicate).

The objects returned will not necessarily be unique (see the note for subjects above).

objects( $subject, $predicate, $graph )

Returns an Attean::API::Iterator of Attean::API::Term objects of all objects of quads matching the supplied pattern (using the same matching semantics as get_quads with an undef object).

The objects returned will not necessarily be unique (see the note for subjects above).

graphs( $subject, $predicate, $object )

Returns an Attean::API::Iterator of Attean::API::Term objects of all graphs of quads matching the supplied pattern (using the same matching semantics as get_quads with an undef graph).

The objects returned will not necessarily be unique (see the note for subjects above).

graph_nodes( $graph )

Returns an Attean::API::Iterator of Attean::API::Term objects of unique subjects and objects present in the specified $graph.

holds($s, $p, $o, $g)

holds($triple_pattern)

holds($quad_pattern)

Returns true if the triple/quad pattern matches any data in the model, false otherwise.

algebra_holds($algebra, $graph)

algebra_holds($algebra, \@graphs)

Returns true if the algebra, evaluated with the supplied default graph(s) matches any data in the model, false otherwise. This is equivalent to the result of an ASK query over the supplied algebra.

evaluate($algebra, [ $default_graph | \@default_graphs ])

Returns an Attean::API::Iterator of Attean::Result objects which result from evaluating the given query algebra (e.g. one obtained from parsing a query with AtteanX::Parser::SPARQL) with the supplied default graph(s) against data in the model.

BUGS

Please report any bugs or feature requests to through the GitHub web interface at https://github.com/kasei/attean/issues.

SEE ALSO

AUTHOR

Gregory Todd Williams <gwilliams@cpan.org>

COPYRIGHT

Copyright (c) 2014--2022 Gregory Todd Williams. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.