A. Borgida. Modeling class hierarchies with contradictions. Technical report, Rutgers University, New Brunswick, 1988.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....transparent as permissible and possible for the application. Updateability of the views is a crucial point in this context. In the recent past, there have been quite a lot of proposals for view systems in OODBMS. These approaches differ with respect to paradigms and aims. Some of the approaches [2, 1, 3, 11, 12] see views mainly as named query expressions and are primarily concerned with the integration of the type of query results into the type lattice of the conceptual schema. Others treat the derived types as separate entities [9] or attach them directly to a root class [10] In [8] an approach ....

A. Borgida. Modeling class hierarchies with contradictions. Technical report, Rutgers University, New Brunswick, 1988.

.... whereas relating such classes to the inheritance hierarchy through an orthogonal relation gives these classes a different conceptual status, making them not concepts themselves, but different points of views (possibly exceptional and therefore involving type incompatibility, as discussed in [Bor88]) of existing concepts instead. In this prototype, we adopted the second alternative since it seems more intuitive and also gives more flexibility to define virtual structures and behaviors, not to mention the simplicity of its implementation compared to that of a complete (and rather complex) ....

Alexander Borgida. Modeling Class Hierarchies with Contradictions. Technical report, Rutgers University, New Brunswick (NJ US), 1988.

.... whereas relating such classes to the inheritance hierarchy through an orthogonal relation gives these classes a different conceptual status, making them not concepts themselves, but different points of views (possibly exceptional and therefore involving type incompatibility, as discussed in [6]) of existing concepts instead. The implementation of imaginary classes is similar to that of virtual classes. In the current implementation, and, we insist, this is a consequence of simplifying assumptions only, a virtual object can be seen as special kind of imaginary object where its root ....

Alexander Borgida. Modeling Class Hierarchies with Contradictions. Technical report, Rutgers University, New Brunswick (NJ US), 1988.

....person isa object [ class person [ 3.1 Inheritance with Overriding and Blocking In ROL2, a subclass can also override or block attribute de nition, default value and method inheritance from its superclasses. Example 11 Consider the following two class de nitions taken from [9]: class patient [ treatedBy )physician default smith ] class alcoholic isa patient [ treatedBy )psychologist ] The rst one says patients are treated by physician with smith as the default physician. In this case, smith must be a physician at the time the class de nition is added to the ....

A. Borgida. Modeling Class Hierarchies with Contradictions. In Proceedings of the ACM SIGMOD International Conference on Management of Data, pages 433-443, Chicago, Illinois, 1988.

....of arguments that are not used for late binding must be more general. If a database schema satisfies these rules, it is said to be behaviorally consistent. However, from a database modelling perspective, the schema must evolve in order to accommodate evolutions of the real world. As argued in [Bor88] this is particularly important in databases where it is in general impossible or undesirable to anticipate all possible states of the world during schema design . The problem is that some schema updates may violate the behavioral consistency rules. For example, consider a database schema that ....

....as implicitly disallowed signatures as they can be inferred from argument exceptions. However, some disallowed signatures cannot be inferred and must be explicitly given by the user as part of the semantics of the application. We call these signatures explicitly disallowed signatures. Following [Bor88] they are defined as excuses on the generic function : excuse m on s 1 , s x . Figure 5: Disallowed signature 6 6 Delta Delta Delta A A AK A A AK Delta Delta Delta Student Salary Resource P rofessor P erson Teaching Assistant Grant Example 3.4 : Consider the schema ....

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A. Borgida. Modeling class hierarchies with contradictions. In Proceedings of the ACM SIGMOD International Conference on Management Of Data, Chicago, IL, June 1988.

....to ours in the context of relational databases. Whereas LOGIN uses hierarchy to create more efficient logic programs, we are using it here to develop a restricted but expressive logic that can be implemented efficiently on a relational database. Inheritance with exceptions has been studied in [5, 6, 8]. These papers have focussed on modeling the class hierarchies, and on language issues, whereas we are studying not just the representation, but also the logic and the implementation, and specifically so in a relational context. An argument has been made for intensional answers to queries (in ....

A. Borgida, "Modeling Class Hierarchies with Contradictions," Proc. ACM-SIGMOD 1988 Int'l Conf. on Management of Data, Chicago, IL, June 1988, pp. 434-443.

....the subclass so that the new method overrides the inherited ones as in O 2 [12] For a class to override an inherited signature (or the corresponding method rule) we can simply introduce a new signature (or a method rule) for this class. Consider the following two class declarations taken from [10]: class patient [treatedBy ) physician] class alcoholic isa patient [treatedBy ) psychologist] They define that patients are treated by physician and alcoholics are patients who are treated by psychologist. But psychologists usually are not physicians. Hence, the subclass alcoholic overrides ....

A. Borgida. Modeling class hierarchies with contradictions. In Proceedings of the ACM SIGMOD International Conference on Management of Data, pages 433--443, Chicago, Illinois, 1988.

....of traditional network representation is that there are problems whose networks are isomorphic to Nixon diamond and yet there is no inherent ambiguity in the problem. For instance, a typical renal failure patient has high blood pressure, while a typical haemorrhage patient has low blood pressure [7]. If a person is known to suffer from both renal failure and haemorrhage, then a physician would conjecture that the patient has low blood pressure. This is because haemorrhage is a stronger evidence to the effect that the person has low blood pressure than renal failure suggests otherwise. ....

A. Borgida, Modeling Class hierarchies with contradictions, in: Proceedings of SIGMOD '88 Conference (1988) 434--443. 7 This would account for the following kind of derivation. Let p is-a q and r is-not-a q are both strict links. Then r is-not-a p.

.... whereas relating such classes to the inheritance hierarchy through an orthogonal relation gives these classes a different conceptual status, making them not concepts themselves, but different points of views (possibly exceptional and therefore involving type incompatibility, as discussed in [Bor88]) of existing concepts instead. In this prototype, we adopted the second alternative since it seems more intuitive and also gives more flexibility to define virtual structures and behaviors, not to mention the simplicity of its implementation compared to that of a complete (and rather complex) ....

Alexander Borgida. Modeling Class Hierarchies with Contradictions. Technical report, Rutgers University, New Brunswick (NJ US), 1988.

....database exactly in the spirit of the architecture proposed by the Ansi X3 Sparc Study Group [oDMS75] We show how the flexibility they provide can be used to cope with various dynamic features of database systems. A number of extensions to the object oriented paradigm have been proposed, e.g. Bor88, RS91, TYH 91, MZ92, Lie86, TYH 91] which try to increase the flexibility of the paradigm and overcome some of its drawbacks. Many proposals have been recently made for the introduction of a view mechanism in object oriented databases [AB91, Ber91, HZ90, RB92, SLT91, SS89, TYI88] An ....

....of C, if any. But class Boss, for instance, has the attribute salary projected out through the hiding operator and its type is not a subtype of the type of C Employee. Approaches to the integration of new classes in the hierarchy includes that of [Run92] where an algorithm is shown, and of [Bor88] where the concept of non strict inheritance is used. Other alternatives include the maintenance of a separate hierarchy for virtual classes, and the definition of a new relationship between virtual and real classes (which is not that of composition nor of inheritance) This last alternative is ....

Alexander Borgida. Modeling Class Hierarchies with Contradictions. Technical report, Rutgers University, New Brunswick (NJ US), 1988.

....GoodStep and PRC BD3. y On leave from Departamento de Inform atica, Universidade Federal de Pernambuco, Brazil. Partially supported by CNPq grant number 200.803 92.1. Multiple inheritance has been shown to be unsuited to model multiple facets of objects dynamically and in a flexible manner [Bor88, RS91, TYH 91, MZ92] Thus, various extensions to the paradigm have been considered, some of which explore the concept of class virtualization [TYI88, AB91, SLT91] the associated idea of defining multiple interfaces to an object [SS89, TYH 91, RS91] the definition of non strict ....

.... 91, MZ92] Thus, various extensions to the paradigm have been considered, some of which explore the concept of class virtualization [TYI88, AB91, SLT91] the associated idea of defining multiple interfaces to an object [SS89, TYH 91, RS91] the definition of non strict inheritance mechanisms [Bor88, Bor89] or alternatives to class inheritance for sharing and extending properties [Lie86, TYH 91] That amounts to a revision of the object oriented paradigm which is driven by database and software engineering as well as knowledge representation (AI) concerns. In this spirit, many proposals ....

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Alexander Borgida. Modeling Class Hierarchies with Contradictions. Technical report, Rutgers University, New Brunswick (NJ US), 1988.

....all the attributes and methods of PERSON, plus the additional ones mentioned in its definition. Furthermore, the invariant stating that (P atients P ersons) is automatically added to the specification. The subclass hierarchy and inheritance are useful for a number of reasons (see for example [4, 6]) including: ffl Abbreviation: the specification of the entire system is made shorter (hence more easily readable) by factoring out commonalities. ffl Propagation of changes: when a super class is changed (e.g. by the addition of a new attribute or by changing the post condition of a method) ....

A. Borgida, "Modeling Class Hierarchies with Contradictions", Proc. ACM SIGMOD '88 Conference, Chicago, May 1988.

....that belong in a requirements model. We briefly consider a variety of abstraction techniques as a way to review relevant research and to suggest possible new directions. Generalization has been particularly favored by our own research, subclass hierarchies with inheritance playing a central role [Borg84, Borg88] as an organizing principle for the contents of conceptual models. It is interesting to note that in requirements modeling, the placement of classes concepts into subclass hierarchies is left entirely up to the human developers. In contrast, researchers in knowledge representation, led by ....

....with the first reading. Similarly, it is not uncommon to find generalization leading to over abstraction (e.g. all patients are assigned to rooms ) so that a subclass may contradict some aspect of one of its ancestors (e.g. emergency room patients may be kept on stretchers in hallways ) In [Borg88], we analyze the conflicting desiderata for subclass hierarchies that allow such improper specialization , and then suggest a simple language facility to accommodate them, while maintaining the advantages of inheritance, and even subtyping. Note however that the above papers deal with the issue ....

A. Borgida, "Modeling class hierarchies with contradictions," Proc. ACM SIGMOD Conf. , pp.434-443, 1988.

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