Extend /mappings/infer to infere mappings by hub vocabulary

[nichtich]

Given a concept A look up all mappings from this concept (A-B₁, A-B₂ ...). Then look up all mappings from B_n to concept in a selected target scheme. Example:

• STW 28023-6 => GND 4003974-2 => DDC 123.5
• GND 4003974-2 => DDC 123.5 => RVK BL 6300

The schemes of middle concepts are used as "mapping hubs".

Two issues:

• number of indirect mappings can get large
• provenance of indirect mappings should be presevered (e.g. as note)
• some indirect mappings can be result of multiple pathes
• this only works for memberSet (see Soergel for approaches for coordinated concept mappings, keep this for later)
• mapping types must be respected

Combination of mapping types:

	=	≈	~	>	<	→
=	=	≈	~	>	<	→
≈		≈	~	~*	~*	→
~			~	~	~	→
>				>	→*	→
<					<	→
→						→

Marked by *: to be discussed

This combination rules (how to infer mappings from other mappings) should be part of jskos-tools.

Query parameters:

• from + toScheme or to + fromScheme
• via=* or via=uris|notations to select which schemes to include as mapping hubs

This gives best results for simple and exact 1-to-1 mappings but should also help in other cases.

[stefandesu]

Maybe as a separate service.

[nichtich]

A first version could be limited to indirect 1-to-1 mappings from a specific concept (from and fromScheme) to another vocabulary (toScheme) via a specific vocabulary (via). The three vocabularies fromScheme, via and toScheme must be distinct. The algorithm would be:

1. Internally call /mappings/infer with via as toScheme to get the primary result set.
2. For each target concept cᵢ in the primary result set, internally call /mappings/infer with the cᵢ as from and original toScheme, so there is a secondary result set for each cᵢ.
3. Iterate the primary result set and use target concept of each mapping together with its secondary result set to infer indirect mappings

This could be provided at /mappings/infer (#177) as well, triggered by the parameter via.

An example: Given three vocabularies A, B, C two mappings and a hierarchical relation:

• Physics in A = Physical sciences in B
• Atomic physics in A is narrower then Physics in A
• Physical Sciences in B < Sciences in C

Query from Atomic Physics in A toScheme C via B:

1. Infer Atomic Physics in A < Physical sciences in B using the hierarchy of A.
2. Combine two mappings Atomic Physics in A < Physical sciences in B < Sciences in C ...
3. ...to infer Atomic Physics in A < Sciences in C.

Worst case performance is when no mapping type is used to restrict inference.