Views, data abstraction, and inheritance in the FUGUE data model

Heiler, Sandra; Zdonik, Stanley B.

doi:10.1007/3-540-50345-5_20

Cited by 20 publications

(9 citation statements)

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“…FUGUE [HZ88] allows multiple instantiation and each type of an object serves as one view onto it. More general view mechanisms are discussed in [HZ90].…”

Section: Related Workmentioning

confidence: 99%

Updatable views in object-oriented databases

Scholl

Laasch

Tresch

1991

Deductive and Object-Oriented Databases

145

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“…FUGUE [HZ88] allows multiple instantiation and each type of an object serves as one view onto it. More general view mechanisms are discussed in [HZ90].…”

Section: Related Workmentioning

confidence: 99%

Updatable views in object-oriented databases

Scholl

Laasch

Tresch

1991

Deductive and Object-Oriented Databases

145

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“…As a consequence of subtyping, objects may be an instance of more than one type. For an object o, each of its types provides a certain view on the object [19]; if viewed as an instance of type T, then only the functions defined in T are applicable to o. The algebra is strongly-typed and allows static type checking [9].…”

Section: The Object Modelmentioning

confidence: 99%

A relational object model

Scholl

Schek

1990

Lecture Notes in Computer Science

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The relational model and its extensions are often considered incompatible with object-orientation.However, on the one hand nested relations provide the complex object features demanded by object models. Particularly, powerful query languages exploit the complex data structure while keeping the advantages of the declarative, set-oriented paradigm. On the other hand, object models provide semantically rich constructs for advanced modeling, and abstractions of operations as well as data. In this paper, we show an evolutionary path from relational, essentially nested relational, to object-oriented data models and query languages. Basically, allowing nested relation schemes to be recursively defined yields the necessary flexibility w.r.t, structure. The query language, i.e., nested relational algebra, carries over to this "network" model. As a first step towards the object-oriented integration of cooperative systems, different views onto the objects have to be supported. We present a powerful view definition facility that basically allows object views as well as relational views to be defined in our object algebra."Why isn't there an object model?" is a question raised in [26]. "How to fit round objects into square databases" is another prominent quotation [45]. These questions reflect important research directions and can be rephrased as "what are the essential differences between object-based and value-based models. , or "how can the advantages of the relational model be kept when the essentials of object-orientation are added?" General agreement exists that the relational algebra with its set orientation, view definition facility, and algebraic optimization are on the pro side for relations. Nested relations and complex objects are extensions which try to keep these advantages [1]. On the OO side the most convincing advantage is the high level of abstraction which is obtained by considering objects as instances of abstract data types, only manipulated by functions, and by organizing the types into a generalization (semi-) lattice.The problem is whether these concepts from both sides can be combined into one model or whether they are incompatible by their very nature. While the integration of two different approaches is an interesting task per se, leading to deeper insight and understanding of the differences and of the similarities, there is a second, practically more important aspect: Providing transformations from one system to another or viewing the same data differently depending on from what system we kx~k at them, is important if we want to or if we have to distinguish several systems. This is necessary and important for application programmers, i.e., application specialists, who develop methods and algorithms to cooperate with the database, for database type implementors who have to integrate or extend existing types by new methods in extensible database systems [43, 11, I8, 33], or database administrators who have to integrate heterogeneous subsystems and various (often existing) applications. Especially to...

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“…In the system proposed by Heiler & Zdonik [Heiler & Zdonik, 1988], for defining an external schema two sets have to be specified: "a set of types and a set of objects that are instances of those types." This is equivalent to specifying a set of classes.…”

Section: [Heiler and Zdonik 1988]mentioning

confidence: 99%

“…External schemas can contain classes not included in the conceptual schema [Tanaka et al, 1988;Heiler & Zdonik, 1988;Dayal, 1989;Abiteboul & Bonner, 1991;Santos et al, 1994;Naja & Mouaddib, 1995;Bertino et al, 1996]. These new classes are derived directly or indirectly from conceptual schema classes, but they are not necessarily included into the conceptual schema.…”

Section: External Schemas Are Not Necessarily Subschemas Of the Conce...mentioning

confidence: 99%

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Definition of external schemas and derived classes in object oriented databases

Samos Jiménez

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El principal objetivo de esta tesis es ampliar el estudio de los esquemas externos en BDOO, en particular, su proceso de definición. Una nueva metodología de definición de esquemas externos que simplifica considerablemente dicho proceso y los resultados obtenidos es presentada. Se considera como referencia el entorno ANSI/SPARC. Los sistemas de definición del esquema conceptual y los esquemas externos están basados en un diccionario de datos. En BDOO, los esquemas externos pueden contener clases del esquema conceptual así como clases derivadas definidas a partir de clases previamente existentes (derivadas o no); las clases derivadas ofrecen vistas de la información contenida en las clases a partir de las que son definidas. La definición de clases derivadas es una cuestión importante en la definición de esquemas externos en BDOO. Por tanto, éste es el segundo tema de investigación. Dos de los problemas principales de la definición de clases derivadas son estudiados: La generación de identificadores para los objetos de las clases derivadas, y la transmisión de modificaciones entre los objetos de las clases derivadas y los de las clases a partir de los que son definidos. Uno de los usos principales de los esquemas externos es proporcionar un mecanismo que soporte la simulación de cambios del esquema. La información en los esquemas externos ha de ser derivada a partir del esquema conceptual; el tipo de cambios del esquema que pueden ser simulados usando esquemas externos es condicionado por este hecho. Por tanto, el tercer objetivo es presentar un mecanismo que soporte la simulación de un espectro más amplio de cambios en el esquema. Este mecanismo está basado en la definición de esquemas externos pero incorpora ampliaciones adicionales. Para proporcionar mayor flexibilidad en este área, proponemos la definición de clases derivadas que puedan contener información no derivada en su intensión y extensión. Cuando un esquema externo con información no derivada ha de ser definido, el esquema conceptual ha de ser modificado para incluir la información no derivada del nuevo esquema. Para evitar modificaciones innecesarias del esquema conceptual el uso de un entorno de prueba para la definición de esquemas externos temporales es propuesto. The main target of this thesis is to broaden the study of external schemas in OODBs, in particular, the external schema definition process. A new external schema definition methodology that considerably simplifies the process of definition and the results obtained, is presented. The ANSI/SPARC framework is taken as a reference. The systems of conceptual and external schema definition are based on a data dictionary. In OODBs, external schemas can contain classes from the conceptual schema as well as derived classes defined from previously existing classes (derived or non-derived); derived classes offer views of the information contained in the classes from which they are defined. The definition of derived classes is an important issue in the definition of external schemas in OODBs. Therefore, the definition of derived classes is the second focus of research. Two of the main problems of defining derived classes are studied: the generation of identifiers for the objects of the derived classes; and the transmission of modifications between the objects of the derived classes and those of the classes from which they are defined. One of the main uses of external schemas is to provide a mechanism that supports the simulation of schema changes. Information in external schemas has to be derived from the conceptual schema; the kind of schema changes that can be simulated using external schemas is conditioned by this fact. Therefore, the third target is to present a mechanism that supports the simulation of a wider spectrum of schema changes. This mechanism is based on the definition of external schemas but incorporates some additional extensions. In order to provide more flexibility in this area, we propose the definition of derived classes that can contain non-derived information in their intension as well as in their extension: partially derived classes. When an external schema with non-derived information is to be defined, the conceptual schema has to be modified in order to include the non-derived information of the new schema. In order to avoid unnecessary modifications of the conceptual schema the use of a test environment for the definition of temporal external schemas is also proposed.

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Views, data abstraction, and inheritance in the FUGUE data model

Cited by 20 publications

References 4 publications

Updatable views in object-oriented databases

Updatable views in object-oriented databases

A relational object model

Definition of external schemas and derived classes in object oriented databases

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