Revisit Retrieval Pipeline

[ppanopticon]

Task Description

In light of the changes introduced in #51, the design of the retrieval pipeline needs slight adjustment. I did not address this in #51 since I'm not too familiar with how the different operators work and what input they expect.

Roughly, I'd propose the following changes:

• [x] The interfaces org.vitrivr.engine.core.operators.retrieve.Aggregator and org.vitrivr.engine.core.operators.retrieve.Transformer can be replaced by the org.vitrivr.engine.core.operators.general.Transformer interface.
• [x] org.vitrivr.engine.core.operators.general.TransformerFactory probably needs some adjustment, to support both retrieval and extraction. Easiest way would be to make the method newTransformer accept Context as parameter instead of IndexContext.
• [x] Existing retrieval operators need to be adjusted. Special attention should be paid to operators that require a specific ordering of incoming elements (e.g., for temporal scoring).

 Dependencies

• May depends on primitives added in #67

Boundary Conditions

None

[ppanopticon]

I assigned this to you @lucaro since you added the existing retrieval operations.

[lucaro]

I'll have a look

[lucaro]

Added relevant changes in https://github.com/vitrivr/vitrivr-engine/tree/feature/68. @ppanopticon please have a look to see if that is along the lines of what you had in mind.

[lucaro]

@ppanopticon any comments?

[ppanopticon]

Looks good to me. If it works we can merge it. I opened PR #71 .

[lucaro]

Done. I did not have the opportunity to extensively test this, but since the changes are only structural and not semantic and it compiles, I don't see much that would have caused a behavioral change.