A handful of existing ontology development methodologies identify “competency questions” as a means of scoping a knowledge model. This post discusses how you can define these questions at the start of your ontology projects for scope-setting purposes, to later use their basis during the assessment phase of your ontologies.
What competency questions are…
Competency questions are user-oriented interrogatives that allow you to scope your ontology. In other words, they are questions that your users would want to gain answers for, through exploring and querying your ontology and its associated knowledge base.
For example, an answer to a competency question could be obtained in simply browsing through a taxonomy and viewing the relationships across the ontology entities, or through the ability to determine inheritance, or through other mechanisms like ontology querying, etc.
What competency questions are not…
Competency questions are helpful to list down but are not compulsory – so, it is up to you to decide whether you want to make use of them. Furthermore, they should not be viewed as an exhaustive list of requirements against which you come up with a test plan to evaluate your ontology and its knowledge base.
Examples of competency questions and scope definition
Say we are interested in developing an ontology of ballpoint pens. Here are a few examples of possible competency questions to help scope our Ballpoint Pen Ontology:
- What characteristics belong to a ballpoint pen?
- Which types of components are common across all ballpoint pens?
- What are the common brands of ballpoint pens?
- Is a kind of ballpoint pen a specialisation of another?
- Can the definition of common types of ballpoint pens be used as a basis to define custom ballpoint pens?
Consequently, we could say that the scope of the Ballpoint Pen Ontology should encompass details of the characteristics and components of ballpoint pens, as well as definitions of custom and common types of ballpoint pens.
Developing and documenting competency questions
Developing competency questions requires you to have an idea of what your domain of interest is, for which your ontology will be a representation of. Information gathering is a key activity to make this happen, especially if you do not have a full command of the subject matter you need to develop an ontology for.
Documenting competency questions as well your goal and scope is best handled as a document at the start of your ontology development methodology. The idea is to keep this information somewhere handy so that you are able to refer to and reuse it easily.
Using competency questions during ontology evaluation
As well as being relevant to the goal and scope definition phase of ontology development, competency questions are also useful during ontology evaluation. These competency questions, coupled with the functional and non-functional requirements you set, allow you to plan the testing of your ontology and knowledge base in a more holistic way.