We demonstrate a system to canonicalise (aka. normalise) SPARQL queries for
use-cases such as caching, query log analysis, query minimisation, signing
queries, etc. Our canonicalisation method deterministically rewrites a given
input query to an equivalent canonical form such that the results for two
queries are syntactically (string) equal if and only if they give the same
results on any database, modulo variable names. The method is sound and
complete for a monotone fragment of SPARQL with selection (equalities),
projection, join and union under both set and bag semantics. Considering other
SPARQL features (e.g., optional, filter, graph, etc.), the underlying
equivalence problem becomes undecidable, where we currently rather support a
best-effort canonicalisation for other SPARQL 1.0. features. We demonstrate a
prototype of our canonicalisation framework, provide example rewritings, and
discuss limitations, use-cases and future work.