This thesis deals with one important aspect of Artificial Intelligence, knowledge representation and reasoning. Problems like knowledge representation hypothesis, production systems, and the proceduralist and declarativist controversy are discussed. The conventional concept of Al system is based on a model where the reasoning and knowledge base are separate. A different model is proposed in this thesis. In this model, the sensory knowledge is considered the basic elements of the knowledge base, and the higher level knowledge form a hierarchical structure. Reasoning power, in this model, is only part of the, knowledge structure. A frame-based knowledge representation system, WenLy, is presented. It is designed to construct a knowledge base from the bottom up, which is conformed to the proposed model in this thesis. The unique characteristic of WenLy is that its reasoning is accomplished by the code imbedded in the knowledge base instead of a separate inference engine. This is the correct approach according to the knowledge structure model herein proposed. An example of the application is shown. WenLy can be used by a robot to represent the robot's understanding of the outside world. The understanding, however, is limited by the bandwidth of the perception capabilities. It can be shown that the conflict between the declarative and procedural aspects of knowledge can be resolved by following the proposed model.