Add predicates for semantic roles.

[proycon]

Right now, semantic roles are not grouped into predicates in FoLiA, whilst semantic roles are typically grouped as such. We need a new span annotation element to remedy this.

Proposal:

<semroles>
  <predicate>
    <semrole class="agent">
      <wref />...
    </semrole>
    <semrole class="theme">
      <wref />...
    </semrole>
  </predicate>
</semroles>

semrole would then require predicate (i.e. semrole would become a span role element rather than a first order span annotation element). This breaks backwards compatibility but is fairly easy to automatically remedy by automatically grouping all semroles in a layer (assuming layers are per sentence as is conventional). Also, I am not aware of anyone already using this annotation type.

[proycon]

The predicates themselves may constitute a new annotation type, as we may want to assign classes based on the verb of the predicate, these can then relate to something like FrameNet.

The oddity would be that a different annotation type (predicates) is then allowed in the annotation layer that's associated with another annotation type (semantic roles). Each takes their own set.

The backward compatibility problem can be prevented in this case by still allowing the old behaviour as well (semrole won't be a span role element but remain a first-order span annotation element).