Expert system has gone through several shifts in view, from search-bas
ed to knowledge-based problem solving and from knowledge transfer to k
nowledge modeling. However, knowledge is still mostly treated informal
ly. There are widely different opinions on its nature. This paper firs
t attempts to characterize knowledge contents within the context of kn
owledge level and then proposes a knowledge structure. Four characteri
stics of knowledge, namely particularity, specificity, bipolarity, and
orthogonality, are identified. They form the components of a multidim
ensional knowledge structure that constitutes a static spatial organiz
ation of knowledge. These components are related together through mult
iple levels of derails and multiple system views. The proposed structu
re creates a taxonomy for classifying knowledge. It brings chaos to or
der by giving meanings to the phenomenon of diverse opinions on knowle
dge.