Odberg, E.: MultiPerspectives Object Evolution and Schema Modification Management for Object Oriented Databases - PhD Thesis, 1995.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....and in the new version in Celsius. The corresponding conversion functions containing the formulae to convert the temperature will be invoked automatically every time this field is updated in either representation. A similar technique is used in the experimental system described in Odberg s work [12], where this technique is called sharing. This system, however, is only a partially implemented prototype. The commercial system GemStone J [6] is based on the Java language, and many of its features are similar to the existing or planned features of PJama. Its evolution facilities, however, are ....

Erik Odberg. Multiperspectives: Object Evolution and Schema Modification Management for ObjectOriented Databases Doctor's Thesis. Department of Computer Systems and Telematics, Norwegian Institute of Technology, February 1995.

....by the evolution tool. 2.2 Specification of Changes at the Level of Classes Currently we can distinguish two main approaches to specifying changes to individual classes. One is simply supplying the new definition of a class to the evolution tool. Another approach (described, for example, in [15]) involves utilisation of some special schema change specification language which usually has much in common with the schema definition language (or is just a part of it) A mix of these approaches may be allowed, as in O 2 [6] The two ways of specifying the change may be compared in Figure 1 ....

....versioning combined with lazy (deferred) conversion, where deletion of attributes is filtered in order to avoid the problem of complex lazy conversion. Information is not physically deleted, but it is no longer usable by applications. No conversion functions are provided. The system described in [15] (it is reported to be designed, but to have only partially implemented prototype) is very different from all other systems reviewed here. Its approach to versioning of class instances is called sharing. This means that the identity of the object whose class has been evolved remains the same, but ....

Erik Odberg. Multiperspectives: Object Evolution and Schema Modification Management for Object-Oriented Databases Doctor's Thesis. Department of Computer Systems and Telematics, Norwegian Institute of Technology, February 1995.

....by commercially available database systems. Object migration includes all mechanisms to allow a single object to change its structure and behaviour during its object life cycle. The migration has to be done dynamically at run time while the object keeps its identity. Role models have been proposed [14, 15, 17, 20, 21] to face that problem and seem to be a good approach to enable for instance the migration of a student object into an employee. This affects only one role of a person, namely his her profession and should be reflected by a partial change of structural and behavioural properties of the ....

....third category of change, modify the structure and behaviour of many objects in the database. Different approaches to schema evolution have been proposed like direct immediate [1, 12] or deferred [3] mechanisms, simulation through views [2, 16, 19] and versioning at the class [13, 18] or schema [5, 9, 10, 14] level. Analogously to object migration supporting the object life cycle we can state that schema updates support the database life cycle by changing its structure and behaviour. This paper presents a data model and an update taxonomy integrating all three categories of change. The idea to use a ....

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E. Odberg. MultiPerspectives: Object Evolution and Schema Modification Management for Object-Oriented Databases. PhD thesis, Norwegian Institute of Technology, 1995.

....by the evolution tool. 2.2 Specification of Changes at the Level of Classes Currently we can distinguish two main approaches to specifying changes to individual classes. One is simply supplying the new definition of a class to the evolution tool. Another approach (described, for example, in [15]) involves utilization of some special schema change specification language which usually has much in common with the schema definition language (or is just a part of it) A mix of these approaches may be allowed, as in O 2 [6] The two ways of specifying the change may be compared in Figure 1. ....

....versioning combined with lazy (deferred) conversion, where deletion of attributes is filtered in order to avoid the problem of complex lazy conversion. Information is not physically deleted, but it is no longer usable by applications. No conversion functions are provided. The system described in [15] (it is reported to be designed, but to have only partially implemented prototype) is very different from all other systems reviewed here. Its approach to versioning of class instances is called sharing. This means that the identity of the object whose class has been evolved remains the same, but ....

Erik Odberg. Multiperspectives: Object Evolution and Schema Modification Management for Object-Oriented Databases Doctor's Thesis. Department of Computer Systems and Telematics, Norwegian Institute of Technology, February 1995.

....forms thus it must always be possible to access the original form, subject to appropriate authorisation. Many researchers have investigated the support of evolution in object oriented database systems [Andany et al. 1991, Coen Porsini et al. 1991, Bratsberg, 1993, Ferrandina et al. 1995, Odberg, 1995, Lerner, 1996, Roddick et al. 1996] They address such problems as adding and deleting class definitions in an existing populated database, and modifying definitions by adding, removing, altering and moving class attributes. Method definitions and any stored queries may have to be altered to ....

Odberg, E. (1995) MultiPerspectives: Object Evolution and Schema Modification Management for Object-Oriented Databases. PhD thesis, Norwegian Institute of Technology.

....of the views. Furthermore, as the dynamic computation of all transformations at runtime might be too time consuming materialized views have to be employed. To avoid the drawbacks of the direct schema evolution approach COAST employs the concept of schema versioning [Eig97, KC88, Lau96, Odb95, Woh96] Here the old states of a schema, which we call schema versions from now on, are not deleted when schema update primitives are executed. Instead, a new schema version is derived in which the updates become effective (see Figure 2) Each application works on top of exactly one schema ....

Erik Odberg. MultiPerspectives: Object Evolution and Schema Modification Management for Object-Oriented Databases. PhD thesis, Department of Computer Systems and Telematics, Norwegian Institute of Technology, February 1995. 408 pages.

.... is a magnitude of formal models for the description of the single components (e.g. Wir90] data type component, Gog94] object component, Har87] dynamic components) and on the other hand there are many approaches which deal with schema modification and database evolution [BKKK87, FMZ 95, Odb95, PO97, SZ87, Zic92] However, only few approaches (as for example [PO97] apply formal description techniques to schema modification. In this paper we try to integrate parts of both of these research directions by combining well known formal description techniques in a schema modification ....

Erik Odberg. MultiPerspectives: Object Evolution and Schema Modification Management for ObjectOriented Databases. PhD thesis, Department of Computer Systems and Telematics, Norwegian Institute of Technology, February 1995. 408 pages.

....the basis of the schema definition, C persistent classes are generated to correspond to the schema classes, and which are used to manipulate persistent objects within C application programs. Additional aspects of the object model not relevant for the discussions in this paper are discussed in [8, 9, 10]. The following illustrates the DDL definition of a class Employee which is a subclass of a class Person not shown here 3 : CLASS Employee : Person string dept; 2 The class interface may contain both methods and attributes; Attributes are abstractly accessible (i.e. through generated ....

....by the association with a predicate in each direction for which a propagation or inhibition is defined. In this paper we will only consider predicates which are C boolean expressions over the attributes of the source class of the classification relationship. Other capabilities are discussed in [8, 9]. The predicate is defined over objects as instances of the class on the source side of classification relationship, expressing which of the source side objects should propagate (over a propagation relationship) or not propagate (due to an inhibition relationship) onto to the target side. In this ....

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Erik Odberg. MultiPerspectives: Object Evolution and Schema Modification Management in Object-Oriented Databases. PhD thesis, Department of Computer Systems and Telematics, Norwegian Institute of Technology, 1994. In preparation.

....role and category classes, is being implemented to demonstrate the applicability of the ideas. Preliminary results are promising. However, the primary focus of our work is within the area of schema versioning, and how different schema versions may contain different versions of the same class. Odb94] will show how the evolutionary and multi perspectived nature of objects have many traits which are similar to the evolutionary and multi perspectived nature of classes, and how many principles of management are the same. Acknowledgments Svein Erik Bratsberg and Reidar Conradi are acknowledged ....

Erik Odberg. MultiPerspectives: Object Evolution and Schema Modification Management in Object-Oriented Databases. PhD thesis, Department of Computer Science, Norwegian Institute of Technology, 1994. In preparation.

....mechanisms even if objects may evolve by changing role possession over time. That is, the abilities to have objects evolve and be multi perspectived does not compromise the importance of the class hierarchy for real world organization conceptual specialization and property inheritance. Odb94b, Odb94c] elaborates on the object role model. 3 Schema Versioning and Schema Version Definition In this section the fundamental aspects of the SMM model are presented. 3.1 Schema versions A fundamental assumption behind our work is that different users may frequently have different perceptions of the ....

....as how these relationships are to be maintained to ensure a semantically consistent database as regarded within any schema version context. The CSL provides general mechanisms for change management, and so that any change, for which a reasonable semantics may be programmed, are permitted. Odb94c, Odb94a] elaborates on the use of the CSL for the definition of change. Schema version compatibility CSL primitives introduced above are concerned about the definition of the contents of the new schema version. While different schema versions are (partially) overlapping specifications of the ....

[Article contains additional citation context not shown here]

Erik Odberg. MultiPerspectives: Object Evolution and Schema Modification Management in Object-Oriented Databases. PhD thesis, Department of Computer Systems and Telematics, Norwegian Institute of Technology, 1994. In preparation.

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Odberg, E.: MultiPerspectives Object Evolution and Schema Modification Management for Object Oriented Databases - PhD Thesis, 1995.

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Erik Odberg. MultiPerspectives: Object Evolution and Schema Modification Management for Object-Oriented Databases. PhD thesis, Norwegian Institute of Technology, February 1995. 408 pages. 1560

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Odb95. Erik Odberg. MultiPerspectives: Object Evolution and Schema Modification Management for Object-Oriented Databases. PhD thesis, Norwegian Institute of Technology, February 1995. 408 pages.

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Erik Odberg. MultiPerspectives: Object Evolution and Schema Modification Management for Object-Oriented Databases. PhD thesis, Norwegian Institute of Technology, 1770 February 1995. 408 pages. page 55 of 56

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