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Rule Documentation

All Packages - Package Correct Operatorgraph - Package Logical Optimization - Package Physical OptimizationFRAMES - NO FRAMES

Rule Variable Propagation

Short Description:

This rule implements variable propagation.

See also:

Constant Propagation of filter with ORs, Constant Propagation

Long Description:

If there are Filter expressions with a value-comparision of two variables, e.g. Filter(?X=?Y), then one of the variables can be propagated to preceding (RDF3X/Hexastore) Index operators in certain cases. However there are problems, if the variables can contain values with ambiguous representations. The values are not identical, but value-equal in this case. These situations might occur when both corresponding variables do not occur in the subject or the predicate of a triple pattern, but only in the objects, which can contain numerical values or language tagged literals. The transformation rule is not applied in these cases.

The following figure contains the graphical representation of the transformation rule.


Variable propagation
All Packages - Package Correct Operatorgraph - Package Logical Optimization - Package Physical OptimizationFRAMES - NO FRAMES