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This article is about the computer science concept. For the sociology concept, see social class.
As in taxonomy, the classifications of species, a class hierarchy in computer science is a classification of object types, denoting objects as the instantiations of classes (class is like a blueprint, the object is what is built from that blueprint) inter-relating the various classes by relationships such as "inherits", "extends", "is an abstraction of", "an interface definition".
The relationships are specified in the science of object oriented design and object interface standards defined by popular use, language designers (Java, C++, Smalltalk, Visual Prolog) and standards committees for software design like the Object Management Group.