TREE relations vs. SHACL constraint components

[bergos]

Is there a particular reason why the tree spec defines its own relations and doesn't use SHACL constraint components? I would see the following benefits:

• SHACL is already used for generated UIs, and that could be reused in case one wants to provide a UI to navigate a tree.
• The tree spec could become shorter as we don't need to define all the semantics for the comparisons.
• SHACL doesn't define geospatial constraint components at the moment. That could be done outside the SHACL spec, and more people would benefit from such a specification.

Drawback:

• It may take longer to add something to the SHACL spec if we identify any gaps.