Sandra Heiler and Stanley Zdonik. Object Views: Extending the Vision. In IEEE Data Engineering, pages 86--93. IEEE Computer Society Press, February 1990.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....that has its own instances (computed upon access) and has its place in an inheritance hierarchy. The main purposes of object oriented views are: providing a logical data independence data hiding and security simplification of a database schema and shorthand for queries data integration [5, 10] simulation of schema changes [4, 11, 14] Although many approaches to object oriented views were proposed in scientific publications [e.g. 1, 2, 3, 4, 5, 6, 7, 10, 11, 14, 15, 17, 18, 19, 20, 21] existing commercial object oriented database systems (Uni SQL and 02) support views to a limited ....

....view definition A concept of object oriented views is based on the object oriented paradigm with the notion of objects, classes, and inheritance. There are two basic approaches to view definition. In the first one a view is defined as a virtual class derived from one [3] or more classes [1, 2, 4, 5, 6, 10, 11, 14, 15, 18, 20, 21], called base classes. The second one defines a view as a portion of a database schema containing virtual as well as base classes [17] This concept was implemented in a MultiView system. In this system a view, called view schema, is constructed in the three following steps: first, virtual classes ....

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S. Heiler, S. Zdonik, Object Views: Extending the vision, Int. Conf. Data Engineering, 1990

....classes forming aggregation hierarchy. 1. 3 Related Work Several approaches to object oriented views were proposed in scientific publications (the review can be found in [20] In the majority of approaches a view is defined as a virtual class derived from one or more classes [1] 3] 4] 5] [9], 10] 14] 17] 18] 19] called base classes. The approaches of MultiView [16] and eXor C [6] 7] consider a view as a more complex structure, i.e. a schema. In MultiView a view is deftned as a portion of a database schema containing virtual as well as base classes. In eXoT C a view, ....

Heiler, S., Zdonik, S.: Object Views: Extending the vision. In proc. Int. Conf. on Data Engineering, 1990

....adding the target class name into the roleSet of the object. Through update propagation, this kind of object migration can also be carried out in the same way as the first situation. 7 Related Work In the recent years, a lot of view mechanisms have been developed for OODBs. Most of them [20] 10][9][1] 17] 15] were realized based on query processing. There are mainly two ways to perform query processing on views. One way is to materialize the derived classes. The other way is to get rid of derived classes by transforming a query into an equivalent set of subqueries which refer to the base ....

S. Heiler and S. Zdonick, Object Views: Extending the Vision, Proc. of IEEE 6th Int. Conf. on Data Engineering, pp.86-93 (1990)

....one lens to another on the same host object, an outside mediator must intervene; delegating the request and en2 abling and disabling the lenses on the host. Likewise, multi threaded behavior becomes troublesome to write. Mechanisms for exporting behavior from the host to the view are explored in [1], as is the question of object identity for objects playing numerous simultaneous roles. The concept of the presenting an interface to a different set of classes is presented as the Adapter Pattern in [3] Using different map objects to vary behavior is an instance of the Strategy Pattern. 7] ....

S. H. amd Stanley Zdonik. Object views: Extending the vision. In International Confernece on Data Engineering, 1991.

....systems having different and diverse needs. The spectrum of the dynamic behavioral requirements is much wider and richer than merely the variation in the object structures (which nevertheless may be complex too) Recently, several approaches to integrate views in OODBMS have been reported (e.g. [1,4,7,9]) However, none of these addresses all the features outlined above. We propose a concept for the separation and integration of external and conceptual schema information in OODBMS which serves all of the above mentioned purposes. In this paper, we put the focus on the type lattices of the ....

S. Heiler, S. Zdonik: "Object Views: Extending the Vision." In: Proc. IEEE Int. Conf. on Database Engineering, Los Angeles, 1990, pages 86-93.

....The CSCW environments of a VE can be shared by more than one user who participates in cooperative work. This is similar to that of defining views in databases for each user. Views are very important in databases where they are used to speed up the query processing on large amounts of data [3, 8, 12, 13, 17, 18, 19]. In this paper, we extend the definition of database view in order to define two types of CSCW environments, namely, local and global environment, for supporting VEs. The local environment defines the available data and operations to each user, and the global environment defines data and ....

S. Heiler and S. Zdonick. Object Views: Extending the Vision. In Proc. of IEEE 6th International Conference On Data Engineering, pages 86--93, 1990.

....how the relations be transformed. Gottlob, Paolini and Zicari [GPZ88] developed a theory of relational view update based on the notion of dynamic views , which is regarded as an association of a data object and a viewing function. In the context of objectoriented databases, Heiler and Zdonik [HZ90] uses a similar notion to provide a viewing mechanism. View object in [Wie86, BSKW91] can also be regarded as an unevaluated viewing function. The general idea of views is also related to roles of objects [RS91, ABGO93] These proposals contain a mechanism to attach multiple roles to objects, ....

S. Heiler and S. Zdonik. Object Views: Extending the Vision. In Proc. IEEE Data Engineering, pp. 86-93, 1990.

....in the object oriented paradigm, views can be used not only for adapting the structure of data to different kinds of applications, but also for redefining the behavior of objects in different contexts. Despite the number of recent proposals of view mechanisms for object oriented databases [AB91, Ber91, HZ90, RB92, SLT91, SS89, TYI88, SDA94], there is very few account on actual implementations [SLT91, KR93] The implementation of views in relational databases has raised a number of interesting issues concerning querying, data integrity, updates and performance [Ker86, Tem86] With objectoriented views, old problems, such as view ....

S. Heiler and S.B. Zdonik. Object Views: Extending the Vision. In IEEE Data Engineering Conference, pages 86--93, Los Angeles, 1990.

....is undecidable in general, we try to identify tractable predicates. Furthermore, reclassification relative to an original class and a specific update operation is simpler than classification in general. 6 Related Work Recently, there have been other proposals for view support in ooDBMSs [1, 5, 10]. These are different from our approach in that we use the standard way of defining views by nothing else than query language expressions. They either introduce special view definition features that duplicate parts of the query language capabilities [1] or use other facilities of their systems. ....

....are different from our approach in that we use the standard way of defining views by nothing else than query language expressions. They either introduce special view definition features that duplicate parts of the query language capabilities [1] or use other facilities of their systems. FUGUE [5] uses type hierarchies for information hiding: the user can implement a new type for the view that uses some base type(s) and offers only a restricted functionality or extends the functionality. Also, not all instances of the base type may be exported. POSTGRES [10] uses the rule system to ....

S. Heiler and S. Zdonik. Object views: Extending the vision. In Proc. IEEE Data Engineering Conf., pages 86--93, Los Angeles, Feb. 1990.

....the source classes, and the view instances are of class Person the view class. Both the source collection classes and the view collection class are set. 8.2. 2 Use of views Many suggestions have been made about and reasons given for the possible use of views in object oriented databases [SS89, HZ90, SLT91, Bra92, Ber92, PMSL94, SAD94] The ones suggested most often are, ffl Information Hiding ffl Support of Versions ffl Information Restructuring ffl Content based Access Control ffl Query Shorthand ffl Integrating Heterogeneous Systems ffl Defining Dynamic Collections ffl Data ....

....complicated and requires constraint checking as well as some trigger mechanism to populate the source collection. Update in scheme A is in some sense information preserving even though it means an inserted element may not appear in the view collection. The notion of value closure is advocated in [HZ90] meaning that only constraint satisfying updates should be allowed. Deletion in scheme A is difficult and requires an expensive computation. On the contrary, deletion in scheme B is straightforward. Scheme A induces schema updates and an instance in a source extent may end up in many view ....

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S. Heiler and S. Zdonik. Object Views: Extending the Vision. In Proceedings of the IEEE Data Engineering Conference, pages 86--93. IEEE Press, 1990.

....commit. In O 2 , the administrator can decide that databases are accessed without logging, i.e. the atomicity and durability properties are abandoned. These mechanisms provide some of the flexibility required by PSEEs. 1.4.2. 3 Abstraction and views Various view definition facilities for ODBSs [67, 23, 1, 47] have been suggested recently. They all enable definition of different interfaces for the same objects. Like in RDBMSs, the view mechanism in most ODBSs suffers from the view update problem. However,O 2 attempts to overcome this problem with its view mechanism. O 2 implements the view mechanism ....

S. Heiler and S. B. Zdonik. Object Views: Extending the Vision. In Proc. of the 6th Int. Conf. on Data Engineering, Los Angeles, CA, pages 86--93. IEEE Computer Society Press, 1990.

....out from applications using the view. The advantage of such a view is that schema modifications do not alter the result of execution of programs using a non side effect view. 2 1 Introduction A variety of view definitions have been defined for object oriented database systems [1] 2] [4], 7] 11] 12] In this paper we study the problem of what happens to a view when the underlying schema and database are updated. We introduce the new concept of non side effect view. A non side effect view is a view which is re computed dynamically so that schema modifications are (whenever ....

S.Heiler, S.Zdonik: "Object Views: Extending the Vision", In Proc. IEEE Data Engineering Conference, Los Angeles, Feb. 1990

....it is displayed using the implementation described earlier. 5.3 Views involving more than one objects A related issue is what should be displayed if the view involves a join of two or more objects. This is a symptom of a general view definition problem in object oriented database systems (see [12] for recent work) We have decided to display all the objects involved in the join simultaneously each displayed using the corresponding display function. 6. RELATED WORK One of the first graphical display systems for databases was the Spatial Data Mangement System [13] An early ....

S. Heiler and S. Zdonik, "Object Views: Extending the Vision", Proc. IEEE 6th Int'l Conf. Data Engineering, Los Angeles, California, Feb. 1990.

....the importance of site autonomy, and the problems associated with a single global schema for the network; however it is designed for the relational database systems and uses INGRES. There are some other related works with respect to the schema integration approach of PEER, such as in [1] [9], and [19] However in our approach, the schema integration and derivation primitives are in some respects more elaborate than the view definition and view update described in those publications, and in some other respects more restricted, in order not to compromise the efficiency of the PEER ....

S. Heiler and S. Zdonik. Object Views: Extending the Vision. In Proceedings Sixth Int. Conf. on Data Engineering, pages 86--93. IEEE, February 1990.

....capabilities of the programming language. This influences the query capabilities, and thus the view capabilities. Theoretical view approaches are typically based on multiple class membership of existing objects in the same [Run92] SLT91] or in a separate type hierarchy [DoE94] SAD94] BDK92] Only [HeZ90] take the generation of new objects into account, while [ChS93] follows a totally different approach of multi valued object identifiers. A comprehensive overview of objectoriented view approaches can be found in [Mot96] In contrast to the amount of theoretical work, available query language ....

....of new objects, there are no update commands in OQL. Object manipulation relies on the existence of update methods for the different objects. Finally, ODMG 93 does not contain a view concept. 3. 1 View Concept Our view concept is based on the object generating approach of Heiler and Zdonik [HeZ90]. However, we extend their approach in order to identify derived objects on the basis of the objects they have been generated from. Each view consists of a set of classes, which are populated with newly generated proxy objects. Each proxy object is a placeholder for an original object providing it ....

Sandra Heiler, Stanley Zdonik: "Object Views: Extending the Vision"; Proc. 6th Intl. Conf. on Data Engineering, IEEE Computer Society Press, Los Alamitos, CA, 1990

....and process data for a product by any one of the three applications may affect the views of the product and process data for the other two applications. In traditional database systems, view management is a well understood problem [5] This is not the case for object oriented data models, however [14, 39]. The added flexibility and complexity of the object paradigm requires that new view creation and management techniques be developed. Creation of a view is no longer a simple task of selecting a subset of the rows and columns in one or more tables, but may require that networks of objects of ....

S. Heiler, and S. Zdonik, "Object Views: Extending the Vision", Proc. IEEE Data Engineering Conference, IEEE Computer Society Press, 1990.

....is particularly tailored for the task performed. Such a subschema consists of a collection of base and or view classes together with the functions defined on them. Some consistency constraints (concerning closure) have to be enforced for subschemas, we do not elaborate on them here (see, e.g. HZ90] Our view mechanism simply allows arbitrary queries to serve as view definitions, exactly as in relational DBMSs: define view name as query ; After the execution of this statement, name will appear as a (persistent) class of the database, just like base classes. The only difference is ....

.... of objects that do not fulfill the selection predicate lead to a problem (the same problem occurs with updates that change the truth value of the class predicate) There are two choices how to react: i) reject such insertions updates (since they violate some kind of closure property [Heg90, HZ90] or (ii) allow them by inserting into the base class updating the object and determining visibility in the view by the selection predicate. Commercial relational DBMSs implement the second choice. Note that the problem is not due to ambiguities in the update translation, but rather one of what ....

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S. Heiler and S.B. Zdonik. Object views: Extending the vision. In Proc. IEEE Data Engineering Conf., pages 86--93, Los Angeles, February 1990.

....integration, like in this paper. It provides security by hiding confidential information. The interpretation of a view as a set of additional integrity constraints [24] is a facet of the security aspect, as well. At a more abstract level, views are just data abstractions from the original database [20], and looking at them from the viewpoint of a daily user, they allow an easy re use of predefined queries. The different implementations of views can be classified along several dimensions: The kind of derivation: There are two ways how query results are obtained. The first is to evaluate a ....

.... means that an existing object may move up and down in the inheritance hierarchy (restricted migration) 2, 10, 11] or may be put into a totally different class, thus keeping the object identifier, but gaining a new behaviour (free migration, multiple class membership multiple instantiation) [8, 20, 29]. Availability of object migration makes things easy. View results are just put into an appropriate class and obtain all the necessary behaviour. Absence of this feature, on the other hand, implies either the usage of global functions for changing behaviour, or the creation of surrogate objects ....

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Sandra Heiler and Stanley Zdonik. Object Views: Extending the Vision. In Proceedings of the 6th International Conference on Data Engineering (Los Angeles, California, February 1990), pages 86--93. IEEE Computer Society Press, Los Alamitos, California, 1990.

.... interest to a particular A book in one library has An article of a specific Books in the Math and the Some books and articles of Table 2: Interschema Relations The set of virtual classes defines a schema and the objects that populate them define a (virtual) database described by the schema [HZ90] The classes used in the definition of a virtual class are called base classes. Extending the concept of a virtual database, a virtual integrated system is defined as a collection of virtual classes populated by virtual (or proxy) objects. A virtual class is a template describing already ....

....this paper, we extend this notion for the case of heterogeneous database systems and show how it can be used as part of the class hierarchy of the global view. View Definition: There are as many approaches to defining object oriented views [DH84, Mot87, AAD 93, Wie86, KDN91, CL92, SLT91, AB91, HZ90, Ber92] as different object based data models. The distinctive characteristic of our approach is that we extend an object oriented programming language, where the only language primitive for grouping sets of objects is the class. Based on that assumption, views in our approach are virtual ....

Sandra Heiler and Stanley Zdonik. Object Views: Extending the Vision. In Proceedings of the 6th International Conference on Data Engineering, pages 86--93, 1990.

....British Columbia, Canada 1992 While the concept of views has been studied extensively in the context of the relational model, it is largely unexplored for OODBs. Initial proposals of views on OODBs have emerged that define a view to be a virtual class derived by an object oriented query [Heil90, Scho91, Kim89]. An object oriented schema is a complex structure of classes interrelated via various relationships, such as, the generalization and decomposition hierarchies [Kim89, Bane87] An objectoriented view should thus be defined to be a virtual, possibly restructured, subschema graph of the global ....

....schemata in Figure 1.c and 1.d are derived from GS by selecting a subset of its classes and interconnecting them into a valid schema using view is a arcs. 2. 3 The Closure of the View Property Decomposition Hierarchy This section addresses the consistency of the property decomposition hierarchy [Tana88, Heil90], while the consistency of the generalization hierarchy is handled in [Rund92c] Let the function Uses(C) represent the set of classes that are used by C s type interface. For example, if p corresponds to an object pointer defined by domain p (C) C2, then Uses(C) contains C2. Definition 11. Let C ....

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Heiler, S., and Zdonik, S. B., "Object views: Extending the vision", in Proc. IEEE Data Eng. Conf., Feb. 1990, pp. 86 - 93.

....and the University of Michigan Faculty Award Program, Intel, and AT T. Harumi Kuno is also grateful for support from the NASA Graduate Student Researchers Program. 1. 1 View System Evaluation A number of researchers have proposed view systems in the context of object oriented databases (OODBs) [5, 9, 13, 12]. However, little work has been done regarding the implementation or materialization of object oriented views [10, 1] As object oriented view systems begin to be offered by prototypes (and later by commercial DBMS engines) we must devise techniques for comparing and evaluating these systems ....

....a materialized view from the time needed to perform the update itself. These updates may involve virtual attributes, i.e. methods. 2 The MultiView View System At the University of Michigan, we have an NFS funded project developing one of the first fully functional view systems, called MultiView [2 5, 10]. MultiView is a view management system capable of supporting updatable materialized object oriented views. The goals of the project include the following: fflUsers should be able to create customized virtual classes at any time. fflUsers should be able to query and update both base and virtual ....

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S. Heiler and S. B. Zdonik. Object views: Extending the vision. In IEEE International Conference on Data Engineering, pages 86--93, 1990.

....set of facilities. The inclusion of method objects would also allow representation of existing programs as objects, and would also be the basis for defining dispatching mechanisms tailored to specific requirements. Method (or function) objects play an important role in the models described in [BEER90, HEIL90, ZHU89], among others. The model would also include explicit mechanisms for modeling messages (invocation requests) invoking methods, binding arguments, and representing expressions. Explicit messages are necessary in a distributed system, and their presence would also allow aspects of less traditional ....

....typically seen in databases, since they may be defined for individual objects. The base object of such a view is effectively the raw material from which the viewdefined interface selects various aspects to be revealed to clients. Variations on extended view mechanisms have appeared in, e.g. [AKSI88, HEIL90, SCHI89]. The browser of [HEBE90] illustrates how a generic function can be considered as a view over the set of messages and objects implementing a multiple dispatching mechanism (or, potentially, vice versa) It should be noted that the proposed model is intended in some cases to be descriptive only. ....

S. Heiler & S. Zdonik, "Object Views: Extending the Vision", Proc. 6th Intl. Conf. on Data Engrg., Los Angeles, Feb. 1990.

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Sandra Heiler and Stanley Zdonik. Object Views: Extending the Vision. In IEEE Data Engineering, pages 86--93. IEEE Computer Society Press, February 1990.

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Heiler S, Zdonik S. Object views: Extending the vision. Proceedings of the 6th International Conference on Data Engineering (ICDE'90). IEEE, 1990; 86--93.

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S.Heiler, S.Zdonik: `Object Views: Extending the Vision', Proc. of the 6th Intl. Conf. on Data Engineering, L.A., California, USA, February 1990.

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