Software people seem to have a love-hate relationship with metrics. On one hand, they despise and distrust anything that sounds or looks like a measu… - Edward V. Berard

Objects are the real and conceptual things we find in the world around us. An object may be hardware, software, a concept (e.g., velocity), or even "flesh and blood." Objects are complete entities, i.e., they are not "simply information" or "simply information and actions." Software objects strive to capture as completely as possible the characteristics of the "real world" objects which they represent. Finally, objects are "black boxes," i.e., their internal implementations are hidden from the outside world, and all interactions with an object take place via a well-defined interface.

In order to better understand object-oriented methodologies in general, it helps to understand the people who make up the "object-oriented community" itself. Far from being monolithic, there is a great deal of diversity within this community. Many object-oriented people, for example, seem to focus almost entirely on programming language issues. They tend to cast all discussions in terms of the syntax and semantics of their chosen object-oriented programming language. These people find it impossible (for all intents and purposes) to discuss any software engineering activity (e.g., analysis, design, and testing) without direct mention of some specific implementation language. Outside of producing executable "prototypes", people who emphasize programming languages seldom have well-defined techniques for analyzing their clients' problems or describing the overall architecture of the software product. A great deal of what they do is intuitive. If they happen to have a natural instinct/intuition for good analysis or good design, their efforts on small-to-medium, non-critical projects can result in respectable software solutions.

An object which is used to create instances, i.e., a template, description, pattern, or "blueprint" of a category or collection of very similar items. Among other things, a class describes the interface the these items will present to the outside world, i.e., the available and appropriate methods, constants, and exceptions. A class represents an abstraction of the items. A class may itself be parameterized (i.e., it actually represents a family of very closely related classes), in which case we refer to it as a parameterized class. Class is a recursive concept. Specifically, we may define classes as being composed of other classes (i.e., heterogeneous composite classes and homogeneous composite classes), in terms of itself (a recursively defined class), as inheriting characteristics from one or more other classes (i.e., the superclasses of the class), and as providing characteristics to other classes (i.e., the subclasses of the class). In some places, classes are defined as "the set of all instances of a type," and the term "type" is given the above definition for class.