How does GATE use ontologies for NLP?

Question

What is the role of ontologies in natural language processing when using GATE?
As I understand it, at a high level, an ontology allows for the modelling of a domain consisting of classes, their instances, properties of these instances and relationships between classes in the domain.

However is there an advantage to creating a custom ontology when working with GATE?
Or can processing be as effective using the only the built in processing resources provided by ANNIE?

Answer 1

You can check this tutorial on ontologies in GATE.

As stated in the pdf:

• Link annotations to concepts in a knowledge base.
• The annotated text is a “Mention” of a concept in the KB
• We can use the knowledge associated with Mentions in our IE pipeline: e.g. Persons have JobTitles, Cities have zip codes
• We can use the knowledge associated with Mentions for “Semantic Search”
• We can use semantically annotated documents to add new facts to our knowledge base

In the process of annotation, ontology data (instances, classes, relations, etc.) can be used by JAPE for smarter matching, i.e. matching a mention with class "engineer", knowing that "engineer" is a subclass of a "person". Also there are ontology-aware gazetteers which can create annotations based on instances and put the right class and uri for the created annotations.

The last two questions are too generic but I'll try...

After following the tutorial, you'll know exactly how to use ontologies for annotation, hence you'll know if you need to create a custom ontology for your task.

ANNIE is an example of a pipeline and a good place to start studying GATE and writing your own application.