A knowledge representation is a way of expressing knowledge for communication (possibly human-to-human, human-to-machine, or machine-to-machine). Refinements include computer knowledge representation.
A knowledge representation can be general (e.g., the Web-page representation of concepts under discussion in and illustrated by this document) or, more commonly, specific to a subject area (e.g., providing special alphabets and notation for expressing mathematical knowledge). Specific subject area knowledge representations might be developed as refinements of a general knowledge representation.
Computer representation of knowledge (a.k.a. machine representation of knowledge) is a knowledge representation that is implemented or implementable in a computer medium, including operations for storing and examining units or collections of represented knowledge, and for searching among them to select certain units or collections. Not all of these operations are necessarily automated in the computer medium.