Gunter Schlageter

A transaction model supporting complex applications in integrated information systems

The use of database systems in new applications, e.g. computer aided design, software engineering, etc, leads to new requirements for the transaction management. Main characteristics of such environments are long duration of transactions and teamwork. In this paper we introduce a concept for lang transactions which especially supports the cooperative work of groups on a common set of data. The transaction model has two levels: on the one hand the team has to be protected from the outside world, on the other hand mechanisms are required which allow controlled teamwork an common objects. In the latter case rigid synchronisation mechanisms as used in database systems are not applicable. A main concept for the support of teamwork and for design databases in general is a user-oriented version mechanism. This paper presents such a mechanism and its integration into the transaction model.

Towards a better support for hypermedia structuring: the HYDESIGN model

Hypermedia systems are becoming an important information system class for a wide range of new and fascinating applications. But current systems still have some unpleasant restrictions. For example, only few hypermedia systems support the design of higher level hypermedia objects beyond the basic node-link paradigm. There are further restrictions concerning the modukuization of the overall design and the reuse of (complex) hypermedia resources. HYDESIGN is the prototype of an extensible hypertext/ hypermedia system which adresses these restrictions. The crucial part of the development is the data management component, the HYDESIGN-engine, which has been built on top of the Gem Stone object-oriented database management system. A first prototype of a graphical user interface, the HYDE SIGN-GUI, has been developed in Smalltalk-80. This paper focuses on central features of the HYDESIGN data model representing the conceptual basis of the HYDESIGN-engine. Aggregate links of differefit types are introduced which allow for the creation of higher level hypermedia networks. SBLnodes represent particular composite nodes offering the capability of defining (nested) local environments with particular behaviour. Also different options for the sharing of hypermedia resources are proposed. HYDE SIGN further supports navigation as well as query based access in an integrated approach. As a whole, HYDESIGN aims at a better support for the hypermedia design process by the provision of powerful structuring facilities. Permission to copy without fee au or part of this material is granted provided that copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to repubtish, requires a fee and/or specific permission. @1992 ACM &89791-547-X/92/~11 /0B2/

Complex and composite objects in CAD/CAM databases

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Redesign of optimistic methods: Improving performance and applicability

It is shown that the concept of interfaces and the concept of composite objects are based on the same mechanism, an instance inheritance relationship. This relationship is integrated into an object-oriented data model which represents interfaces and composite objects in an easy way. The concept of interfaces is generalized to an abstraction mechanism. This allows some severe drawbacks of a rigid interface concept to be eliminated and generic component relationships to be needed.<<ETX>>

Object-Oriented Database Systems: Concepts and Perspectives

The original approach of optimistic concurrency control /2/ has some serious weaknesses with respect to validation, long transactions and starvation. This paper first discusses design alternatives which avoid these disadvantages. Essential improvements can be reached by a new validation scheme which is called snapshot validation. The paper then discusses a validation scheme which especially supports read transactions, so that the number of backups decreases substantially. Finally a very simple solution for the starvation problem is presented. The proposal is perfectly consistent with the underlying optimistic approach.

OOPS-an object oriented programming system with integrated data management facility

During the last years object-oriented database systems have become a major topic in database research. A large number of research institutes are working on individual aspects or complete system prototypes. However, there is still much confusion about which features make up such a system. This paper attempts to define the main features and characteristics. It distinguishes between a basic definition and an extended definition. The latter tries to cover some more extensive requirements for object-oriented database systems as they are introduced by non-standard applications. Moreover, the paper attempts to identify the most important variants by which a feature may be realized and shows some open fields for research work.

A collaborative lab- and learning environment for a virtual database-practical at the virtual university

OOPS is an object-oriented programming environment with integrated data management facilities. It is designed to especially support advanced applications, like engineering and office applications. Rich data modeling facilities, including the concepts of classification, generalization, and aggregation are provided. Additionally, complex semantic integrity constraints, exception-handling mechanisms, and triggers can be specified. Since all these facilities are integrated into a single language, the artificial distinction between database language and programming language is no longer existent. The main features of the programming language and the architecture of OOPS are presented.<<ETX>>

Problems of optimistic concurrency control in distributed database systems

This paper introduces an authentic learning environment with an authentic database laboratory for collaborative distance teaching. We developed and established a three-server-environment for a new type of database practical that is in its first testing cycle. It offers an environment capable of providing all the services that would be needed for a practical that requires a whole semester but no physical presence of the student. Bearing in mind the special requirements of distance education we tried to develop an environment to realize our didactical goals. On the one hand the environment consists of an administration and communication environment: The virtual university that provides access to and information about the course. On the other hand we provide the groupware environment BSCW (Basic Support for Cooperative Work) for shared documents and further communication. The laboratory component is an ORACLE instance with team-accounts accessible via the iSQL*Plus browser interface.

State-of-the-art of long-term preservation in product lifecycle management

In [SCH81] some aspects of optimistic concurrency control (CC) in distributed database systems have been discussed, some important problems have, however, not been dealt with in sufficient detail in the paper but only in the oral presentation. Thus, the reader of the conference proceedings might get the impression that optimistic CC, as introduced in [KUR79], is very easily adapted to distributed systems. Unfortunately, when looking into the problem more thoroughly, the contrary turns out to be true. This note is meant to highlight the main problems of optimistic CC in distributed database systems. We cannot discuss possible solutions in detail - this will be done elsewhere.

TOPAZ: A Tool Kit for the Construction of Application-Specific Transaction Managers

Providing access to digital information for the indefinite future is the intention of long-term digital preservation systems. One application domain that certainly needs to implement such long-term digital preservation processes is the design and engineering industry. In this industry, products are designed, manufactured, and operated with the help of sophisticated software tools provided by product lifecycle management (PLM) systems. During all PLM phases, including geographically distributed cross-domain and cross-company collaboration, a huge amount of heterogeneous digital product data and metadata is created. Legal and economic requirements demand that this product data has to be archived and preserved for a long-time period. Unfortunately, the software that is able to interpret the data will become obsolete earlier than the data since the software and hardware lifecycle is relatively short-lived compared to a product lifecycle. Companies in the engineering industry begin to realize that their data is in danger of becoming unusable while the products are in operation for several decades. To address this issue, different academic and industrial initiatives have been initiated that try to solve this problem. This article provides an overview of these projects including their motivations, identified problems, and proposed solutions. The studied projects are also verified against a classification of important aspects regarding scope and functionality of digital preservation in the engineering industry. Finally, future research topics are identified.