Cached join

[GMMULLER]

If a join is specified in the grammar using the integration_scheme it will be checked if that join already exists. To determine if a join exists it is checked:

• spatial_relation
• in and out
• in and out levels
• abstract

There is checking regarding the operation (aggregation and custom function). That works well if in and out are physical layers or knots because the operation is applied in a later step but when in is a thematic layer the join is stored with the operation already done. This difference should be considered somehow.