Node validation

[ftomassetti]

Should we have a standard way to report issues on nodes?

This could be useful for integrating editors with other components (i.e., editors would consume issues by displaying them).

It could also be useful if we wanted to have pipelines: a component could get a model, perform resolution on it, and add issues for things that are inconsistent (for example, calling a method with the wrong number of parameters).

[dslmeinte]

I think it'd be useful, because it's a chance to define how to pinpoint a certain location within a model, e.g. (ID, [feature, [index within value]]).

[enikao]

I think we need to separate two cases:
a. How to handle technically invalid nodes sent along. There are different levels:

• Invalid JSON (syntax error)
• Missing / unknown JSON entries
• Inconsistencies (e.g. parent/child mismatch)
• Unknown node ids
• Unknown concepts / features

b. Handle nodes inconsistent with metamodel, e.g.

• Reference out-of-scope
• child link not part of parent concept
• constraint violations

For a), we need to think how a server reacts if it gets a "write request" where parts of the data is invalid. Don't do anything? Apply the valid changes? In the latter case, how do we report back which parts worked?

For b), I think we only need to talk about reporting -- each LIonWeb system needs to decide on its own how to handle them.

[joswarmer]

Good separation of the two cases. The first one is essential for the API, as the client needs to know whether something sent is applied or not and why.

[enikao]

Relates to #88