Alan H. Borning. Classes versus Prototypes in Object-Oriented Languages. In Proceedings of the ACM/IEEE Fall Joint Computer Conference, pages 36--40, Dallas, Texas, November 1986. 24  Home/Search   Document Not in Database   Summary   Related Articles   Check

....in lieu of inheritance or classes. LaLonde has developed an implementation of Smalltalk that uses prototypes (he calls them exemplars) LaLonde 86] Borning has proposed a constraint based inheritance mechanism to maintain inheritance relationships in a system where classes and prototypes coexist [Borning 86] Refinement Self [Ungar 87] is a prototype based programming language based on the notion that all computation is a process of refinement of shared behavior. Self, like actor languages, takes a behaviorist s view of programming: An object is what it does. In Self, the number 3 is viewed as a ....

....[Decouchant 86] ProxyObjects, however, are full fledged Smalltalk objects, while Decouchant s proxies are part of the private data of the Object Manager portion of his resident virtual machine. ffl A number of researchers have observed the problems associated with subclassing and inheritance [Borning 86, Lieberman 86, Synder 86, LaLonde 86, Sandberg 86] 1 A transparent forwarding mechanism similar to the one used in Distributed Smalltalk has been independently developed by McCullough [McCullough 87] Accent [Fitzgerald 85] achieves similar results through different means. Accent avoids ....

Alan H. Borning. Classes versus Prototypes in Object-Oriented Languages. In Proceedings of the ACM/IEEE Fall Joint Computer Conference, pages 36--40, ACM and IEEE, Dallas, Texas, November 1986.

....constraining [Tai93] As opposed to class based systems, in prototype based systems there are no classes; new objects are formed directly by constructing concrete, full fledged objects, which are referred to as prototypes or exemplars. A prototype can be thought of as a standard example instance [Born86], which represents the default behavior for some concept [Lie86] Prototype based systems provide no classes, and therefore in these systems there is no notion of instantiation either. Prototype based systems can be divided into three different elementary categories [Tai93] namely copy based, ....

....is tricky to use since it requires the ability to duplicate and join multiple objects simultaneously. Classification is unachievable in this model, since no relations exists between the original and the copy after cloning, which makes it impossible to carry out group manipulation. Alan Borning [Born86] proposed that the problems of groupwise modification in the copybased approach can be avoided using relations that exist between objects and are set up during the process of copying. The delegation based approach utilizes a delegation mechanism to provide an incremental modification capability ....

Borning, A.H., Classes versus prototypes in object-oriented languages. In Proceedings of ACM/IEEE Fall Joint Computer Conference, November 1986, pp.36-40.

....This means that an object A may be defined to inherit the behaviour of object B, which is conceptually equivalent to the fact that A delegates its behaviour to B once and for all. 2.2. 2 Use of Delegation The concept of delegation, although not really widely known and used, is not a new concept [24, 25]. It has also been proposed for use with graphics systems [25, 26] and in animation [27] It has, however, never become widely accepted by the computer graphics community. The only example of its usage within the context of multimedia, that we are aware of) is for the Event Script language of ....

....of object B, which is conceptually equivalent to the fact that A delegates its behaviour to B once and for all. 2.2. 2 Use of Delegation The concept of delegation, although not really widely known and used, is not a new concept [24, 25] It has also been proposed for use with graphics systems [25, 26] and in animation [27] It has, however, never become widely accepted by the computer graphics community. The only example of its usage within the context of multimedia, that we are aware of) is for the Event Script language of the Athena Muse project [28] 1 . This, in spite of the fact that ....

A. Borning, "Classes versus prototypes in object-oriented languages," in 1986 Proceedings of the IEEE/ACM Fall Joint Computer Conference, (Dallas, Texas), pp. 36--40, November 1986. 12 An Object Model for Multimedia Programming

....with the one achieved by delegation in prototype based languages. We also point out that there are two possible semantics for delegation links. 1 Introduction Prototype based languages are traditionally opposed to class based ones and many comparisons between them have already been proposed [4, 15, 12, 11]. More specifically the delegation mechanism, which is part of many prototype based languages [1, 8] has been compared to the class inheritance mechanism appearing in class based languages. Both mechanisms are inheritance mechanisms and achieve some kind of sharing. The one achieved by delegation ....

A.H. Borning. Classes versus Prototypes in Object-Oriented Languages. In Proceedings of ACM/IEEE Fall Joint Computer Conference, pp. 36--40, 1986.

....update. Page 2 The reliance on method update is one of the most unusual aspects of our formal treatment: this operation is not normally found in programming languages. However, method update can be seen as a form of dynamic inheritance [25] which is a feature found in object based languages [7] but not yet in class based languages [6] Like other forms of dynamic inheritance, method update supports the dynamic modification of object behavior allowing objects, in a sense, to change their class dynamically. Thus, method update gives us an edge in modeling object based constructions, in ....

Borning, A.H., Classes versus prototypes in object-oriented languages. Proc. ACM/IEEE Fall Joint Computer Conference. 1986.

....implemented on a 32 node nCUBE2. References: 142] 2.73 Obliq Developer: Digital Equipment Corporation, Palo Alto Description: oo. Object based language, related to Modula3. There are no classes. Inheritance is implemented by object cloning, i.e. Obliq is a prototype based language. See [34] for the original prototype based language proposal. memory model. parallelism. Additional activities are introduced by fork and join commands. The join command can wait upon the completion of names threads and returns the return value of the forked procedure. scheduling. A thread can decide to ....

A. H. Borning. Classes versus prototypes in objectoriented languages. In Proc. of the ACM/IEEE Fall Joint Computer Conf., 1986.

....objects and classes are commonly referred to as class based languages. Objectbased language that do not offer classes but offer a mechanism to clone objects, i.e. to make several objects that adhere to a common interface and implementation are called prototype based languages (see for example [40]) The difference between classes and Ada s packages [4] is that classes determine types of the language. Objects of a class instantiate this type. Packages cannot be used to instantiate objects, but are only used to encapsulate types. Class based programming languages enforce a programming ....

A. H. Borning. Classes versus prototypes in object-oriented languages. In Proc. of the ACM/IEEE Fall Joint Computer Conf., 1986.

....of class de nitions (as well as other run time modi cations of 2 the class hierarchy) Thus the complete class hierarchies are not known at compile time or at any stage preceding the actual program execution. CLOS [20] and Smalltalk are two such languages. Additionally, prototype based languages [3, 5, 33] are also examples of such languages. Name resolution in presence of late binding is easily solved for static object oriented languages (such as Java and C ) since the complete class hierarchy is known at compile time; simple table lookups allow for constant time name resolution. For dynamic ....

....f class circle : public shape f protected: oat side; oat radius; char name; public: public: public: void display( void display( void display( f . g f . g f . g g; g; g; In an application program it is possible to de ne an array of pointers to shape: 6 shape array[5]; circle little circle(2.0) square big square(100.0) and successively assign to it values taken from the subclasses circle and square, e.g. array[0] little circle; array[1] big square; The execution of the methods array[0] display( and array[1] display( should lead to the ....

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A. Borning. Classes versus Prototypes in Object Oriented Languages. In Fall Joint Computer Conference. ACM/IEEE, 1986. 29

....experience also leads us to develop a classless (prototype based) object model for Cecil. We feel that a classless object model is simpler and more powerful than traditional class based object models. Cecil s object model is somewhat more restricted than those in other prototypebased languages [Borning 86, Lieberman 86, LaLonde et al. 86, Ungar Smith 87, Lieberman et al. 87] in response to other design goals. Since message passing is the cornerstone of the power of object oriented systems, Cecil includes a fairly general form of dynamic binding based on multiple dispatching. Multimethods ....

A. H. Borning. Classes Versus Prototypes in Object-Oriented Languages. In Proceedings of the 1986 Fall Joint Computer Conference, pp. 36-40, Dallas, TX, November, 1986.

....to method update. The reliance on method update is one of the most unusual aspects of our formal treatment: this operation is not normally found in programming languages. However, method update can be seen as a form of dynamic inheritance [25] which is a feature found in object based languages [7] but not yet in class based languages [6] Like other forms of dynamic inheritance, Page 2 method update supports the dynamic modification of object behavior allowing objects, in a sense, to change their class dynamically. Thus, method update gives us an edge in modeling object based ....

Borning, A.H., Classes versus prototypes in object-oriented languages. Proc. ACM/IEEE Fall Joint Computer Conference. 1986. Page 13

....is one of the most unusual aspects of our formal treatment. This operation is not normally found in programming languages, with some exceptions (for example: Beta [22] Obliq [12] Method update can be seen as a form of dynamic inheritance [31] which is a feature found in object based languages [10] but not yet in class based languages. Like other forms of dynamic inheritance, method update supports the dynamic modification of object behavior allowing objects, in a sense, to change their class dynamically. Thus, method update gives us an edge in modeling object based constructions, in ....

Borning, A.H., Classes versus prototypes in object-oriented languages. Proc. ACM/ IEEE Fall Joint Computer Conference, 36-40. 1986.

....46 The first question that arises in the context of objects that are potential units of concurrent execution is whether and in which cases they can have multiple threads of execution active at a time. 39 See e.g. Cox86] 40 cf. e.g. Sny86, Weg87, Str88] Mey88, page 59] 41 See e.g. Bor86, US87] 42 cf. e.g. Pap92] 43 For discussions on these issues see e.g. KL89, TS89] 44 See also [Pap92, Chapter 3] 45 For discussions on a variety of concurrent programming constructs see e.g. AS83, And91] This approach is adopted in object oriented languages such as, for example, ....

A. Borning. Classes versus Prototypes in Object-Oriented Languages. In Proceedings of the ACM/IEEE Fall Joint Computer Conference, pages 36--40, Dallas, Texas, November 1986.

....typing involves a choice between safety and flexibility. The flexibility offered by dynamically typed object oriented languages is useful in exploratory programming but may also be a hindrance to safety checking and optimization when delivering products. Henry Lieberman [9] and Alan Borning [3] developed the notion of objectoriented languages based on prototypes. The absence of classes and types in these languages yields a considerable flexibility which may be significantly increased by the notions of dynamic and multiple inheritance. These language constructs, however, make safety ....

Alan H. Borning. Classes versus prototypes in object-oriented languages. In ACM/IEEE Fall Joint Computer Conference, pages 36--40, 1986.

....object implementing the data abstraction. 2.1 Objects and Inheritance Cecil has a classless (prototype based) object model: self sufficient objects implement data abstractions, and objects inherit directly from other objects to share code. Several other prototype based models have been proposed [Borning 86, Lieberman 86, LaLonde et al. 86, Ungar Smith 87, Lieberman et al. 87] Cecil uses a classless model primarily because of its elegance and simplicity. Our approach to object oriented multi methods, however, does not hinge on this decision; our approach also could be adopted in a class based ....

A. H. Borning. Classes Versus Prototypes in Object-Oriented Languages. In Proceedings of the 1986 Fall Joint Computer Conference, pp. 36-40, Dallas, TX, November, 1986.

....their formulas [5, 20, 12, 25] The mark phase is our primary interest in this paper, since it uses the dataflow edges in the constraint graph to determine which constraints must be marked invalid. 2. 3 Editing Model Our editing model is similar to one supported by a prototype instance model [4, 15]. An application can create instances of any object. All attributes, parts, and formulas associated with the object are inherited by the new instance. The original object is called the prototype of the new instance. Until an object is instanced, the following editing operations are permitted: ffl ....

BORNING, A. H. Classes versus prototypes in object-oriented languages. In Proceedings of the ACM/IEEE Fall Joint Computer Conference (Nov. 1986).

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Alan H. Borning. Classes versus Prototypes in Object-Oriented Languages. In Proceedings of the ACM/IEEE Fall Joint Computer Conference, pages 36--40, Dallas, Texas, November 1986. 24

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Borning, A.H. Classes Versus Prototypes in Object-Oriented Languages. In Proceedings of the ACM/IEEE Fall Joint Computer Conference. 1986.

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A. Borning. Classes versus prototypes in object-oriented languages. In ACM/IEEE Fall Joint Computer Conference, pages 36--40, Dallas, Texas, USA, Nov. 1986.

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A. H. Borning, `Classes versus prototypes in object-oriented languages', ACM/IEEE Fall Joint Computer Conference, November 1986.

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Alan H. Borning, `Classes versus prototypes in object-oriented languages', ACM/IEEE Fall Joint Computer Conference, 1986, pp. 36--40.

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A. H. Borning. Classes versus prototypes in object-oriented languages. In ACM/IEEE Fall Joint Computer Conference, pages 36--40, Dallas, TX, 1986.

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A.H. Borning. Classes versus Prototypes in Object-Oriented Languages. In Proc. of the IEEE/ACM Fall Joint Conference, pages 36-- 40, 1986.

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Alan Borning. Classes versus Prototypes in object oriented Languagues. In Proceedings of the ACM/IEEE Fall Joint Computer Conference, November 1986.

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A. H. Borning. Classes Versus Prototypes In Object-Oriented Languages. In ACM/IEEE Fall Joint Computer Conference, November 1986.

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A. H. Borning. Classes versus prototypes in object-oriented languages. In ACM/IEEE Fall Joint Computer Conference, pages 36--40, Dallas, TX, 1986.

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