Member extraction part of TREE specificaiton.

[xdxxxdx]

Thanks for providing the example to illustrate TREE and LDES — a small comment from my side.

As I understand it, the SHACL shape is not mandatory for extracting the member: TREE. also It's primarily used to extract a member from the graph rather than to validate it (although it can also be seen as a result of the extraction process).

Maybe it is better start with CBD in the example https://github.com/rorlic/ldes-docs/blob/main/step-by-step/D-tree-specs.md#validating-members.

Then move to shapeTopology, might be better wait for this PR is settlehttps://github.com/TREEcg/specification/pull/143/files.