Converter

• Converters rule implement Converter and convert from one convention to an another.
• Converter rules applied via convert

A ConverterRule converts between calling conventions.

Example:

• indicates what system will actually execute the query by assigning a particular call.

Transformer

A rule that match a subtree of a relational algebra expression and replace it with a different subtree. ie it is a rule to transform an relational expression to another.

Example: exchange the order of Filter and a Project nodes.

Match: Transformer Rules are matched to elements of a query plan using pattern matching. onMatch is called for matched rules

Example: RelOptRulesTest.java