Discussion of GATE’s Onto Root Gazetteer

In Instructions for GATE’s Onto Root Gazetteer, I have information to set up Onto Root Gazetteer. In this post, I discusses aspects of the Onto Root Gazetteer that I found interesting or problematic.

For me, the documentation was not helpful as too much technical information was provided (e.g. preprocessing the ontology) rather than the steps just to get it to run. Also, no walk through example was clearly illustrated. I would still like (and will provide in the near future) a richer text (a nice paragraph) and a simpler ontology (couple of classes, subclasses, object and data properties, and individuals) to illustrate just what is done fully.

Though I have it running, there are several questions (and partial answers or musings):

  • What is the annotation relative to the ontology good for?
  • What is the difference between gazetteers derived from ontologies and default gazetteers?
  • What is the selection criteria for annotating the tokens?
  • What is the relationship between the annotated text and the ontology?

Concerning the first point, presumably more annotations allow more processing capabilities. A (simple) example would be very helpful.

Concerning the second point, matters are more complex (to my mind). First, default gazetteers (or flexible gazetteers for that matter) are flat lists (a list containing no sublists as parts) where the items in the list are annotated as per the properties of the list; for example, if we have a gazetteer for Organisation (call this the header of the list) which lists IBM, BBC, Hackney Council (call these the items of the list), then every token of IBM, BBC, and Hackney Council found in the corpus will be annotated Organisation. If there is a token organisation in the corpus, it will not be annotated with Organisation; similarly, no token of IBM in the corpus is annotated IBM. The list categorises, in effect, IBM, BBC, and Hackney Council as of the type Organisation.

ORG works differently (I believe, but may be wrong), but these points are not made in the documentation. First, a gazetteer which is derived from an ontology preserves the subsumption hierarchy of the ontology, giving us a list of lists. Such a gazetteer is a taxonomy of terminology, which is not the same as an ontology (though frequently mistaken to be identical). Second, if a token in the text is found to (flexibly) match an item in the gazetteer, then the token is annotated with that item, meaning that if the string IBM is a token in our text and an item in the gazetteer, then token is annotated IBM. In these respect, ORGs work differently from other gazetteers.

The third question might be addressed in the richer documentation concerning ORG. It relates to observations concerning the results of the example application. Consider the following. The token “language resources” has the annotation:

URI=http://gate.ac.uk/ns/gate-ontology#LanguageResource, heuristic_level=0, majorType=, propertyURI=http://www.w3.org/2000/01/rdf-scheme#label, type=class

The token “resources” has the annotation:

URI=http://gate.ac.uk/ns/gate-ontology#GATEResource, heuristic_level=0, majorType=, propertyURI=http://www.w3.org/2000/01/rdf-scheme#label, type=class

And the token “parameters” has annotation:

URI=http://gate.ac.uk/ns/gate-ontology#ResourceParameter, heuristic_level=0, majorType=, propertyURI=http://www.w3.org/2000/01/rdf-scheme#label, type=class

We see that the tokens in the text are annotated in relation to the ontology. Yet it is not clear why the token “resources” is not annotated with LanguageResource or ResourceParameter since these are components of the ORG as well. Likely there is some prioritising among the annotations that we need to learn.

Finally, concerning the last question, matters are somewhat unclear (to me) largely because the line between annotations, gazetteers, and ontologies are blurred, where for me the key unclarity focuses around annotations in the text that match items in the gazetteer. Consider the issue from a different point of view. ORG was developed in the context of a project to support ontology development from text — find terms and relations which are candidates for the ontology, then (if one wants) use the terms and relations to build the ontology. For example, if one sees lots of occurrences of “organisation” in the text, then perhaps it would be introduced as a concept in the ontology. We have a many-one relation from the tokens to the ontology. This makes sense. See it another way, where we have a default gazetteer where every given token (e.g. IBM) in a text has the same annotation, giving the impression of a one-many relation. This also makes sense. Neither of these seem problematic to me largely because I don’t really know much or presume much about the meaning of the annotation on the token: from the text, I abstract the concept, from the gazetteer, I label tokens as belonging to the same annotation class. In no case is a token “organisation” annotated with Organisation; even if it were, I couldn’t really object unless I said more about what I think the annotation means.

Contrast these points with what goes on with ORG (admittedly, this gets pretty philosophical, and in terms of day to day practice, it may not be relevant). First, it seems that one instance in the ontology is associated with multiple tokens in the text. Second, an instance or class in the ontology can be associated with a token that is intended to have some similar meaning — e.g. the individual IBM in the ontology is associated by annotation with every token of IBM in the text, and similarly for the classes. Neither of these make sense to me in terms of what ontologies are intended to represent, which is a state of knowledge (the fixed concepts, object and data properties, and individuals) about a domain. On the first point, how can I be assured that the intended meaning of tokens is the same throughout the corpus? In one document, we might find IBM as the name of a non-existent company, in an other for an existing company, and in another for a company that has gone bankrupt. Simply put, the string might remain the same, but the knowledge we have about it may vary. Ontologies (as they are currently represented) do not allow such dynamic interpretation. To ignore this point risks having annotations (and whatever might flow from the annotations) slip; for example, it would be wrong to find a relationship between IBM and owners where the company doesn’t exist. On the second point, conceptually it makes no sense to say that a token “organisation” is itself associated with the concept or instance or ‘organisation’ in the ontology. Or course, in developing the ontology, going from the text to the ontology makes good sense since one is abstracting from the text to the ontology. Yet, in that move, one makes something different — a concept over all the “ideas” drawn from the tokens. So, I disagree emphatically with Peters and Maynard (from the NeON article): “Texts are annotated with ontology classes, and the textual elements function as instances of these classes.” The textual element “organisation” or “IBM” is an instance of the concept organisation or the individual IBM? I think this is a category mistake.

In general, I find the relationship between the text, intermediate representations (gazettees), and ontologies (higher level representations of knowledge) rather interesting, but somewhat murky. As I said earlier, perhaps this is just philosophy. Depending on the domain of discussion, the corpus, and the way the annotations and ontologies are used, perhaps my intuition of lurking trouble will not be realised…. Equally, there is likely something simple that I’m missing. If so, please enlighten me.

By Adam Wyner
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