With our knowledge of the application environment, or domain knowledge and knowledge of the intended audience,natural language understanding system could not properly comprehend the phrases and sentences they process. What we need ,then,is a suitable way to represent such knowledge to the sytems. For this reason, artificial intelligence researchers are preoccupied with what is known as knowledge representation. It is basically the "glue" that binds much of ai together, but it has its own set of problems.