PSPARQL regular expression patterns

Introduction

Let I be the set of irirefs, B be the set of blanks, and X be the set of variables. The regular expression patterns used in the PSPARQL query language are constrcuted inductively over I∪B∪X in the following way:

• ε is a regular expression pattern;
• ∀a∈I∪B∪X, a and !a are regular expression patterns;
• if A and B are regular expression patterns, then (A), +A, *A, A|B, and A.B are regular expression patterns.

Examples

The following regular expression pattern generates words of length at least one that contains train or bus repeated many times:

+(train | bus)

The following regular expression pattren generates words, which are of length two, that contains any symbol other than train followed by avion:

!train . avion

Constrained regular expressions

The constrained regular expressions allowed in CPSPARQL Grammar are the ones constructed over the set of urirefs, blanks, and variables.

We use { and } to denote the begining and the end of a constrained regular expression that will be applied to the constraint. The inverse, positive and kleene operators will be prefixed. For example, + ( {-ex:from} % const1 % . ex:to ) is a constraint regular expression, the constraint in this example will be applied to the part -ex:from. See also the Grammar.