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out.setMetadata(input.getMetadata().clone()); |
Query Rewrite (Step 3)
Rewriting is used to switch, add, remove or replace logical operators before they are transformed into their physical counterparts. Normally, the aim of the rewriting process is to optimize the query, for example, by pushing down selection operator before costly joins. The implementation is done by rewriting rules, which are implemented like transformation rules (see next section).
Transformation (Step 4)
To translate the logical operator into the physical counterpart the transformation engine is needed. The rule for the route operator can be found in the following example. Further information can be found in the description of the transformation component.
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