2 - Logic expressions

Abstract

This chapter presents a discussion of logic expressions. This discussion is supported with the example of the process of making an automatic device for controlling access to a bank vault. In finding an answer to this question, the chapter arrives at a form of algebraic expression that always evaluates to either 0 or 1. To arrive at the simplest form of these expressions, a graphical method and a tabular method for simplifying logic expressions can be employed. In the example, three employees of a bank have access to the vault: the manager, the assistant manager, and the chief cashier. In order to obtain access to the vault, any two of these persons must present themselves before an incorruptible person, the controller, who decides if access to the vault is permitted. The controller makes a “truth table,” which is used to determine whether or not, access to the vault is permitted. When bank employees present themselves before him, he asks three questions: (1) is the manager present, (2) is the assistant manager present, and (3), is the chief cashier present. The answers to these questions are either “Yes” or “No.” Based on the answers given, the decision is taken by looking it up in the truth table and employing logic expressions.