Module transformations

Fileoverview

The steps a rewriting pipeline is built out of, one factory each.

Every step is a <descriptiveStem>Transformation() returning a types!QueryTransformation, so that a pipeline reads as a uniform list; only the unfolding has anything to configure, and it is the only one taking arguments.

• unfoldingTransformation: the rewriting proper - every triple pattern replaced by the mapping body producing the triples it could match. Takes the mapping it unfolds, and whether to preserve cardinality.
• rewriteNonRecursivePathsTransformation: expands non-recursive property paths into equivalent BGPs and UNIONs, so the unfolding sees individual triple patterns. Belongs before the unfolding.
• filterFalseTransformation: removes FILTER(FALSE) patterns, what they stand over, and the structures containing them (UNION identity, JOIN absorbing element), sub-SELECTs included; a GROUP and the query's own solution modifiers are left in place.
• pushDownAssertionsTransformation: pushes assertion filters (FILTER(sameTerm(?x, c))) as deep into the plan as possible, substituting into BGPs, pruning VALUES rows and UNION branches, and turning an OPTIONAL over an asserted variable into a plain join.
• pullUpExtendsTransformation: the mirror of the pushdown, floating the BINDs it left behind at the leaves back up the plan and deleting the ones nothing above reads - a UNION every branch of which carries the same bind included.
• nullifyJoinOverIncompatibleBoundsTransformation: detects joins whose branches bind a variable to incompatible terms and replaces them with FILTER(FALSE).
• nullifyUnbindableVarsTransformation: the same one level up, for incompatible term types rather than terms.
• removeProjectionsTransformation: removes all inner PROJECT operations, anonymizing every non-projected variable to a fresh one to preserve scoping.
• joinValuesToFilterTransformation: rewrites a JOIN with a VALUES clause into an equality FILTER over the remaining operands, enabling further push-down.
• extendsToValuesTransformation: rewrites a BIND of a ground term over the empty BGP or over a VALUES into a VALUES itself.
• serviceCallPushUpTransformation: merges and hoists SERVICE calls so as much of the plan as possible is evaluated by the endpoint.
• internalBnodeAsSpecialLiteralTransformation / internalBnodeAsSpecialIriTransformation: materialise internal blank nodes as typed literals or as prefixed IRIs, since RDF 1.1 sources cannot reference blank nodes consistently.

One step is deliberately not re-exported here: comunica!simplifyStaticExpressionsTransformation, which folds static expressions through Comunica's expression evaluator. It bootstraps Components.js from Node's module resolution, so importing it reaches node:module and node:path; a bundler resolves every import in a module graph before it tree-shakes, so re-exporting it here would make this barrel - and with it the package entry point - unresolvable for the browser even in a build that never calls the step. It lives behind the sparql-view-unfold/comunica subpath instead, which only a Node consumer needs to reach for.