Definitions:
Knowledge representation is a umbrella term for the methods by which information is stored in the mind for later use. - by Arthur B. Markman, 2005
Knowledge representation is a subarea of artificaial intelligence concerned with understanding, designing, and implementing ways of representing information in computers so that programs can use this information to: derive information that is implied by it; to converse with people in natureal languages; to plan future activities; and solve problemsin areas that normally require human expertise. - by Stuart C. Shapiro, 2005
book: Knowledge representation by Arthur B. Markman, 1999 http://books.google.com/books?id=Ytys7EgskXsC
「表徵」一詞在不同的學科中，有不同的意涵。在1950s後期，心理學開始以電腦的觀點研究心智。這種觀點假設人類的心智就像電腦一樣，以表徵完成演算工作，以此觀點來說明人類心智處理資訊的工作。在心理學中，廣義的表徵(representation)可以用四個部分來定義(Markman, A., 1999)：
知識表徵是一個人工智能研究的次領域，探討理解、設計、與以計算機實作表徵資訊的方式。因而得以：
導出(derviing)資訊中隱含的資訊以推論(reasoning)的形式表徵。因此這個領域的研究又被稱為「知識表徵與推論」。
許多哲學家認為知識(knowledge)即被證明(justified)為真的信念(true belief)。但是在人工智慧的知識表徵研究中，對知識的定義並不侷限在如此嚴謹的哲學定義中。
知識表徵研究開始於1958年左右，目標在於使電腦能夠處理人類所能進行的常識判斷。1960s-1970s的知識表徵研究，認為人們都是以自然語言處理知識表徵與資訊的使用。1970s-1980s的研究關注於人類專業作業的特定領域知識。1980s-1990s，研究轉為關注於日常生活知識中的特定次領域細節，如時空表徵(spatial representation)、一般目的的知識架構(ontology; Cyc Project)。
predicate calculus - 謂詞演算
在1800s-1900s初期，發展出許多希望能將人類的推論邏輯加以計算的形式系統(formal system)，或可統稱唯一種形式邏輯系統。對人工智能的研究者而言，這是知識表徵系統的濫觴。這時期所發展的系統由三種基本要素組成：
meaning
在邏輯系統中有兩種meaning:
propositional logic 與 predicate logic (first-order logic) 在邏輯語法上的不同
In the mid-1970s, knowledge representation researchers were embroiled in what was called the 'declarative/procedural controversy'.
know-what/know-how
Production systems are a subclass of knowledge representation and reasoning systems. The knowledge base of a production system is divided into two parts, a working memory and a rule memory. The working memory consists of a set of symbol structures not containing varialbes. The rule memory consists of a set of pattern-action rules.