====== Logic-Based Representation ======

===== About logic-based representation =====

**Natural language** is the most **expressive** knowledge representation formalism we have. However, it is hard to model and reasoning becomes very complex. The other **problems with natural language** are **ambiguity** of natural language, **understanding** of syntax and semantics, and **little uniformity** in the structure of sentences.

**Logic** was developed as an attempt to overcome the problems with natural language by creating a **formal language** based on mathematical principles. Logic-based representation should be **expressive, unambiguous, context independent, and compositional**. Logic-based representation requires the following concepts to be defined [1]:
  * **Vocabulary**: a collection of symbols represented as chars, words, icons, or even sounds. 
  * **Syntax**: a logic must have grammar rules that determine how symbols combine to form well-formed sentences.
  * **Semantics**: it is necessary to make meaningful statements. It comprises a theory of reference that determines how the constants and variables relate to things in the universe of discourse. Moreover, it also includes a theory of truth to distinguish true statements from false. 
  * **Inference**: carried out by rules that determine how patterns are generated from others. Appropriate inference rules allow reasoning mechanisms automation and, thus, the generation of new knowledge from previous one.
===== Technologies =====

==== First-order predicate logic ====

First-order logic is a formal system used in mathematics, philosophy, linguistics, and computer science. It is also known as first-order predicate calculus, the lower predicate calculus, quantification theory, and predicate logic (a less precise term). First-order logic is distinguished from propositional logic by its use of **quantified variables**.

===== Tools =====

==== Prolog ====

==== Other tools ====



===== Bibliography =====

  - [[http://rhizomik.net/html/~roberto/thesis/html/KnowledgeRepresentation.html|Roberto García. A Semantic Web Approach to Digital Rights Management]]. Retreived April 28, 2012.
===== Read more =====

  - [[http://www.scarpaz.com/2100-papers/Logics/9-baader97logicbased.pdf|Franz Baader. Logic-based Knowledge Representation]]
  - H. Reichgelt. "Knowledge representation: an AI perspective". Ablex Pub. Corp., 1991
  - [[http://www.cs.utexas.edu/~mooney/cs343/slide-handouts/fopc.4.pdf|University of Texas at Austin: First Order Predicate Calculus]]