Support for relation extraction #7
Description
Right now, skweak supports two main types of NLP tasks: (token-level) sequence labelling and text classification. Both rests on the idea that labelling functions associate labels to text spans, and the role of the aggregation model is then to merge the outputs of those labelling functions such as to get unified predictions.
However, some NLP tasks cannot be easily associated to text spans. For instance, relation extraction necessitates a prediction on pairs of spans.
The question is then how to provide support for such type of tasks, for instance by implementing a RelationAnnotator that could be used to associate pairs of spans to a label.
Technically speaking, we could still encode the annotations internally as SpanGroup objects. One solution would be to only add one span of the pair in the SpanGroup, but then specify that this span is connected to a second span (SpanGroup objects allows the inclusion of JSON-serialised attributes). The method get_observation_df in the BaseAggregator class could then be extended to detect whether a span is a normal one, or is connected to a second span. If that is the case, the aggregation would then be done on pairs of spans instead of single spans.
Do get in touch if this functionality is something you need, so that we know whether we should prioritise this in our next release :-)