
Rule Documentation

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 valuecomparision 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 valueequal 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.