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...one level of abstraction are shielded fromsimplementation details at lower levels of abstraction.sLiskov goes as far as to suggest that "for abstraction to work, implementations must besencapsulated" =-=[53]-=-. In practice, this means that each class must have two parts: an interfacesand an implementation. The interface of a class captures only its outside view, encompassingsour abstraction of the behavior...

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...ing is most frequently used to model conceptual hierarchies. When used in this way, a subtype describes a type that is more specific than a supertype; the subtype is a specialization of the supertype =-=[53, 74]-=-. 5MS-DOS is a trademark of Microsoft Corporation. 15 Inheritance can be used in several ways; some clarify the design of a framework while others can make a framework more difficult to understand. On...

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... object o 1 of type S there is an objectso 2 of type T such that for all programs P defined in terms of T , the behavior of P is unchanged when o 1 is substituted for o 2 , then S is a subtype of T . =-=[14]-=-. Behavioral notions of subtyping that attempt to capture this substitutability property have since been defined by many, including America [1], Leavens and his colleagues [12, 13, 3], Meyer [18], and...

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...as possible. Inheritance has clear advantages in prototyping systems. However there appear to be real dangers of excessive complexity when long subclass chains are left in large systems. Others (see (=-=Liskov, 1988-=-; Snyder, 1986), for example) have cautioned about the dangers of loss of encapsulation in inheritance. A related problem is that minor changes in a superclass can invalidate method definitions lower ...

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... that the system was built over a period 1993 to 1994, when far less guidance was available with regard to "good" or "proper" use of inheritance. Research work such as Liskov's substitution principle =-=[18]-=- had not permeated into standard practice and design heuristics such as [19] were not published until OO software was more established. Second, the classes with the highest defect densities were found...

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...s perform logically atomic updates to the abstraction's state; and each operation must maintain the consistency of that state. Support for such abstractions in sequential languages is well understood =-=[30, 34]-=-, but the situation is more complex for concurrent languages [1, 43, 17, 2, 4, 9, 24, 22]. Concurrency allows only a partial order on state updates, complicating the notion of consistency. Any concurr...

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... in on individual aspects, and the design guidelines that enable the inclusion or exclusion of an aspect to be made a configurable option in a software system. Barbara Liskov’s substitution principl=-=e [13] g-=-ives the conditions under which a derived class can be considered a genuine subtype of its super-type. The principle is stated as follows: “If for each object o1 of type S there is an object o2 of t...

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...ject types in the class hierarchy, including any class invariant that may be imposed. From the point of conformance to OO semantics, most analysis techniques uphold Liskov’s Substitutivity Principle (=-=Liskov 1988-=-) on behavioral subtyping. Under Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distrib...