[0.5.0] Composability

[Disiok]

Conceptual changes

• Decouple index structure and data

V2IndexStruct is no longer a BaseDocument.

• We introduce CompositeIndexStruct to model a composed graph

This makes ComposableGraph is very similar to BaseGPTIndex. We could unify this further later.

• Model relationship between indices via IndexNode

IndexNode is a Node with a pointer to an IndexStruct
We no longer "set_text" on a IndexStruct, which breaks various abstractions. The same can be expressed as creating an IndexNode with some summary text, and point it to the IndexStruct.

Storage

• We use DocumentStore to store data (i.e. Document and Node)

This eliminates many ugly "if this is an index struct, do X, otherwise do Y" logic.

• We save V2IndexStruct separately

To support saving and loading polymorphic objects, we always save its type along with the actual object

Querying

• Remove recursive logic from BaseGPTIndexQuery

Now recursive logic is entirely managed via QueryRunner. This removes mutual recursion and make things easier to reason about.

• Introduce def retrieve and def synthesize API

This makes it explicit which queries support recursive call vs. not.

Misc Change (WIP)

• group common params into ServiceContext object

We basically pass these around across all data objects. This is mostly an attempt to make code cleaner.

Todos

• [ ] Figure out how to deal with query type to query map
• [ ] Fix composability for tree
• [ ] Fix query combiner support
• [ ] Lint and tests
• [ ] Clean up BaseGPTIndexQuery ctor mess