Knowledge representation (KR) is a branch of AI, but not at hot/popular/attractive to young AI researchers as other fields, such as machine learning (ML).
However, it matters. (I will explain later in this post why it is not as popular as machine learning.)
Allow me to use one example. I am writing an email to Dr. H. I usually write to Dr. H while CC'ing to Dr. X on issues about research topic A. But today, I do not CC to Dr. X but Dr. Z because today's email is about research topic B.
Gmail, maybe using some statistic strategy, thinks I put Dr. Z by mistake and suggests me to put Dr. X in the CC field.
You may say, oh gosh, Gmail is too stupid to know that email recipients are related to email topics - this so common-sense!
How can Gmail know that common sense knowledge? This could be a difficult learning problem. How do we know it? We may even learn this from other kinds of human communications, like, how mom manages family meetings - for some topics you are excluded and for some topics boys are excluded.
To improve Gmail, how can we tell this common-sense knowledge to it? There must be some fancy ways in ML. But, a very, very, easy approach is tell this knowledge to Gmail: ``Email recipients are related to topics.''
Now we need KR!
KR provides an easy way to pass human knowledge to computers, just like how professors teach in classrooms. Why let the computers re-learn knowledge known to humans?
In the end, why KR isn't as hot as machine learning? I feel that young investigators like topics that can bring practical results, such as ``making a smarter planet.'' Most KR researchers I know care more about solving fundamental problems. I hope to see young KR investigators preaching the gospel of KR to real applications.
This year I collaborated with a PhD student whose research is about robotics. His work is about letting robots efficiently find objects visually. We were stunned by how common sense knowledge can boost the performance of robots.
If you wanna know more, please stop by our poster at AAAI-12. We will buy you ice cream later - do they sell ice cream in Canada? I mean, unlike Texas, that's a chilly place.