# Boolean expression

You are comparing two floating point numbers and at least one number is the result of an arithmetic operation. Oracle recommends that you use the ABS and ROUND functions to do approximate tests for equality and avoid all three causes of unexpected comparison failure. Controlling Errors Due to Numerical Precision Suppose expense is a decimal variable whose value is set by a calculation. The laws Complementation 1 and 2, together with the Boolean expression laws, suffice for this purpose and can therefore be taken as one possible complete set of laws or axiomatization of Boolean algebra. Every law of Boolean algebra follows logically from these axioms.

Furthermore, Boolean algebras can then be defined as the models of these axioms as treated in the section thereon. To clarify, writing down further laws of Boolean algebra cannot give rise to any new consequences of these axioms, nor can it rule out any model of them.

In contrast, in a list of some but not all of the same laws, there could have been Boolean laws that did not follow from those on the list, and moreover there would have been models of the listed laws that were not Boolean algebras.

This axiomatization is by no means the only one, or even necessarily the most natural given that we did not pay attention to whether some of the axioms followed from others but simply chose to stop when we noticed we had enough laws, treated further in the section on axiomatizations. Or the intermediate notion of axiom can be sidestepped altogether by defining a Boolean law directly as any tautology, understood as an equation that holds for all values of its variables over 0 and 1.

All these definitions of Boolean algebra can Boolean expression shown to be equivalent. Duality principle[ edit ] Principle: There is nothing magical about the choice of symbols for the values of Boolean algebra. But suppose we rename 0 and 1 to 1 and 0 respectively.

Then it would still be Boolean algebra, and moreover operating on the same values. But if in addition to interchanging the names of the values we also interchange the names of the two binary operations, now there is no trace of what we have done.

## Boolean Expressions

The end product is completely indistinguishable from what we started with. When values and operations can be paired up in a way that leaves everything important unchanged when all pairs are switched simultaneously, we call the members of each pair dual to each other.

The Duality Principle, also called De Morgan dualityasserts that Boolean algebra is unchanged when all dual pairs are interchanged.

One change we did not need to make as part of this interchange was to complement. We say that complement is a self-dual operation. The identity or do-nothing operation x copy the input to the output is also self-dual. There is no self-dual binary operation that depends on both its arguments.

## Expression

A composition of self-dual operations is a self-dual operation. The principle of duality can be explained from a group theory perspective by the fact that there are exactly four functions that are one-to-one mappings automorphisms of the set of Boolean polynomials back to itself: These four functions form a group under function compositionisomorphic to the Klein four-groupacting on the set of Boolean polynomials. Walter Gottschalk remarked that consequently a more appropriate name for the phenomenon would be the principle or square of quaternality. There is one region for each variable, all circular in the examples here.

The interior and exterior of region x corresponds respectively to the values 1 true and 0 false for variable x. The shading indicates the value of the operation for each combination of regions, with dark denoting 1 and light 0 some authors use the opposite convention.

While we have not shown the Venn diagrams for the constants 0 and 1, they are trivial, being respectively a white box and a dark box, neither one containing a circle.

## Java Regular Expression Example

However we could put a circle for x in those boxes, in which case each would denote a function of one argument, x, which returns the same value independently of x, called a constant function.

As far as their outputs are concerned, constants and constant functions are indistinguishable; the difference is that a constant takes no arguments, called a zeroary or nullary operation, while a constant function takes one argument, which it ignores, and is a unary operation.

Venn diagrams are helpful in visualizing laws.Atoms¶. Atoms are the most basic elements of expressions. The simplest atoms are identifiers or literals. Forms enclosed in reverse quotes or in parentheses, brackets or braces are also categorized syntactically as atoms.

Here are some examples of Boolean algebra simplifications. Each line gives a form of the expression, and the rule or rules used to derive it from the previous one. A basic Boolean expression has this form: expression relational-operator expression.

Java evaluates a Boolean expression by first evaluating the expression on the left, then evaluating the expression on the right, and finally applying the relational operator to determine whether the entire expression evaluates to true or false..

For example, suppose you have declared two variables.

## XML Schema Part 2: Datatypes Second Edition

(expression) Any sub-expression enclosed in parentheses. For example, (3 + 2) * 2 forces 3 + 2 to be evaluated first. mod() round() abs() Function schwenkreis.com function name must be immediately followed by an open-parentheses, without any spaces or tabs in between. It's not an "implicit assumption," it's what the compiler's doing.

The b expression, the same as if it were used for an if statement. The expression evaluates to a boolean, which is then returned.. Also noteworthy, you seem to interchange boolean and Boolean as though they're the same, but they're actually schwenkreis.comn is the primitive form while Boolean is an Object that wraps a.

In computer science, a Boolean expression is an expression in a programming language that produces a Boolean value when evaluated, i.e. one of true or false.A Boolean expression may be composed of a combination of the Boolean constants true or false, Boolean-typed variables, Boolean-valued operators, and Boolean-valued functions..

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Comparison of different SQL implementations