Browsing by Author "Alhajj, Reda"

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    Query model for object-oriented databases
    (IEEE, 1993-04) Alhajj, Reda; Arkun, M. Erol
    A query language should be a part of any database system. While the relational model has a well defined underlying query model, the object-oriented database systems have been criticized for not having such a query model. One of the most challenging steps in the development of a theory for object-oriented databases is the definition of an object algebra. A formal object-oriented query model is described here in terms of an object algebra, at least as powerful as the relational algebra, by extending the latter in a consistent manner. Both the structure and the behavior of objects are handled. An operand and the output from a query in the object algebra are defined to have a pair of sets, a set of objects and a set of message expressions where a message expression is a valid sequence of messages. Hence the closure property is maintained in a natural way. In addition, it is proved that the output from a query has the characteristics of a class; hence the inheritance (sub/superclass) relationship between the operand(s) and the output from a query is derived. This way, the result of a query can be persistently placed in its proper place in the lattice.
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    Schema changes in an object-oriented database system
    (ASME, 1992) Alhajj, Reda; Arkun, M. Erol
    Proper and efficient handling of schema changes is an important aspect of any object-oriented database management system. Clearly, it is desirable for an object-oriented database management system to satisfy as many schema operations as possible. This paper deals with schema changes in ODS; an object-oriented database management system prototype. A brief description of the basic features of ODS along with its storage and indexing models are included to facilitate the treatment. The invariants of the class hierarchy/lattice as well as the rules for resolving ambiguities due to schema changes are discussed. In addition, schema changes handled by ODS are described. Schema modifications are done through the user interface of ODS that provides both a class browser and a programming shell. Versions are supported by ODS in handling both methods and messages. For composite objects name conflicts are handled by considering both superclasses and nesting classes.
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    View maintenance in object-oriented databases
    (Springer, 1996-09) Alhajj, Reda; Polat, F.
    in this paper, we present a model that facilitates view maintenance within object-oriented databases. For that purpose, we differentiate between two categories of classes, base classes and brother classes. While the former constitute the actual database, the latter are introduced to hold virtual database, i.e., views derived from base classes. To achieve incremental view update, we introduce a modification list into each base class. A series of algorithms are developed to serve the purpose. Finally it happened that, view maintenance within object-oriented databases subsumes that within the nested and hence conventional relational models.