NAME

RDF::Trine::Pattern - Class for basic graph patterns

VERSION

This document describes RDF::Trine::Pattern version 1.018

METHODS

new ( @triples )

Returns a new BasicGraphPattern structure.

construct_args

Returns a list of arguments that, passed to this class' constructor, will produce a clone of this algebra pattern.

triples

Returns a list of triples belonging to this BGP.

type

sse

Returns the SSE string for this algebra expression.

referenced_variables

Returns a list of the variable names used in this algebra expression.

definite_variables

Returns a list of the variable names that will be bound after evaluating this algebra expression.

clone

bind_variables ( \%bound )

Returns a new pattern with variables named in %bound replaced by their corresponding bound values.

subsumes ( $statement )

Returns true if the pattern will subsume the $statement when matched against a triple store.

merge_patterns ( @patterns )

Given an array of patterns, this will merge them into one.

sort_for_join_variables

Returns a new pattern object with the subpatterns of the referrant sorted based on heuristics that ensure firstly that patterns can be joined on the same variable and secondly on the usual selectivity (i.e. how quickly the engine can drill down to the answer) of triple patterns. Calls subgroup, sort_triples and merge_patterns in that order.

subgroup

Splits the pattern object up in an array of pattern objects where the same triple patterns occur. It will group on common variables, so that triple patterns can be joined together is in a group together. It will also group triples that have no connection to other triples in a group. It will then order the groups, first by number triples with common variables, then by number of literals, then by the total number of terms that are not variables.

sort_triples

Will sort the triple patterns based on heuristics that looks at how many variables the patterns have, and where they occur, see REFERENCES for details. Returns a new sorted pattern object.

BUGS

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

REFERENCES

The heuristics to order triple patterns in this module is strongly influenced by The ICS-FORTH Heuristics-based SPARQL Planner (HSP).

AUTHOR

Gregory Todd Williams <gwilliams@cpan.org>

Kjetil Kjernsmo <kjetilk@cpan.org>

COPYRIGHT

Copyright (c) 2006-2012 Gregory Todd Williams. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.