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:

• Vocabulary it is 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: this aspect is important in order to get something more than a notation. Inference is 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.

requirements: vocabulary…

first order predicate logic

prolog

other tools

1. Roberto García. A Semantic Web Approach to Digital Rights Management. Retreived April 28, 2012.