A knowledge engineer’s job is to mine domain knowledge from human subject matter experts. The domain knowledge is the knowledge in a particular field of expertise.
The Ins and Outs of Domains
The domain can’t just be “everything” or “all knowledge.” It would be too difficult to cover everything in the knowledge base. You don’t have to depend only on one subject matter expert; you could keep using more and more to try and cover “all knowledge.” But even if you had the time and the resources to capture all this knowledge, it would also be impractical to connect users with particular problems to the right reasoning and guidance offered by the system if it covered all domains.
For example, let’s assume you’re trying to help a user who needs to make a magical potion. There’s a potential domain here: magic (or in J.K Rowling’s universe, witchcraft and wizardry). But this domain is still too broad, at least for the purposes of our expert system and the problem it seeks to solve.
So let’s narrow it down to subjects you can take at the Hogwarts School of Witchcraft and Wizardry. (I’m willing to bet this example will be easier to understand and remember than the one I’ll include after it)
To solve the problem for our non-expert who needs to make a magical potion, we can call “potions” our domain. Our knowledge engineer is the one who has the domain knowledge.
A less whimsical example could involve a non-expert who needs guidance to obtain a grant of probate for an estate. “Law” is a potential domain, but it’s probably too broad to be helpful for our problem. Law can be broken into subjects like criminal prosecution, real estate, intellectual property and so on. The specialized subject of “probate & estates” will be the right domain for our problem.
The Human Link to the Domain Knowledge
In most cases, the subject matter expert has done all the work to build up his or her own specialized knowledge about the domain. This expert will have an exceptional understanding of the domain in terms of what it includes or excludes, what happens within it, what language or words are used for it, and how other actors interact with or within it.
Good subject matter experts will also know how the problem happens to, of for, non-experts. They will have strong indications of what a good outcome will look like for non-experts, and the guidance required to take them there. Experts who bring a purely academic or theoretical understanding may be unable to provide the right reasoning and guidance the knowledge engineer needs to make the expert system capable of helping non-experts.