1-Knowledge Representation:
The process of acquisition of knowledge could be carryout manually or
automatically. In manual mode, knowledge receives from one or more domain
experts. whereas in automatic mode, a machine learning system is used for
autonomous learning and refining knowledge from the external world.
Now knowledge after acquisition can be represented by various tools and
techniques such:
1) Logical representation uses expressions in formal logic to represent its
knowledge base. Predicate Calculus is the most widely used representation
scheme.
1-1 Propositional Calculus.
1-2 Predicate Calculus.
2) Procedural representation represents knowledge as a set of instructions for
solving a problem. These are usually if-then rules we use in rule-based systems..
3) Network representation captures knowledge as a graph in which the nodes
represent objects or concepts in the problem domain and the arcs-represent
relations or associations between them.
3-1 Semantic Nets Representation.
3-2 Conceptual Graph.
3-3 Frames and Scripts Representation.
3-4 Petri Nets Representation
4) Structured representation extends network representation schemes by allowing
each attached values. Node to have complex data structures named slots with
attached values.
We will focus on logic representation schemes in this chapter.
1.1 The Propositional Calculus
Symbols and Sentences
The prepositional calculus and, in the next subsection, the predicate calculus are
first of all languages. Using their words, phrases, and sentences, we can represent
and reason about properties and relationships in the world. The first step in
describing a language is to introduce the pieces that make it up set of symbols.
DEFINTION
PROPOSITIONAL CALCULUS SYMBOLS
The symbols of prepositional Calculus are, the prepositional symbols:
P. Q. R,S,T.... are truth symbols
true, false
and connectives :
Prepositional symbols denote propositions of statements about the world that
may be either true or raise, such as "the car is red" or "water is wet." Propositions
are denoted by uppercase letters near the end of the English alphabet. Sentences in
the propositional calculus are formed from these atomic symbols according to the
following rules :