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.

Document image archives are increasingly used to replace paper and microfilm filing. Usually those archives are combined with a database management system or with full text retrieval to search the documents. An additional retrieval method to search already known images in personal document image archives using layout knowledge is presented. This knowledge can be the size, position, and color of layout objects, but also the position of keywords. A layout editor is proposed, which allows the interactive generation of a layout query using object oriented drawing functions. The layout search can be done in a relational database, which was filled with the help of layout recognition methods. For better results and performance special search methods and structures are necessary. Examples for those methods are quad trees to locate layout objects at absolute positions, neighborhood tables to find object pairs with certain spatial relationships, and full text search in page or object areas.>

Interoperability of programming languages with persistency requires new concepts to make a single knowledge base management system (KBMS), a custom-tailored tool for applications of various programming languages and of different programming paradigms. The authors describe a method for the horizontal integration of KBMS applications from different programming languages. They used the commonly known ADT definition technique to maintain a vertical integration between languages and the KBMS, and propose schema sharing and polymorphism as the background for this particular kind of interoperability. The suggested approach was validated by an extended KBMS object manager, the conceptual object manager. Some of the design principles of the conceptual object manager, the vertical integration task, and the semantics of the horizontal integration are considered.>

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.>

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.>

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.

No abstract available.

A non-procedural query language for network databases is described. The language is very powerful as compared to other implemented languages. It allows to formulate complex queries which, among other things, include conditions for CODASYL-sets and conditions for n:m-relationships. Cyclic database structures can be processed to some extent.Note: This report is not written for the "naive" user of NOAH, and is not meant to replace a NOAH manual. Instead, this report describes the foundations, the underlying concepts, and the structure of the language in more theoretically oriented, technical terms.This research was performed at the university of Hagen, West Germany, and was partially supported by Triumph Adler AG, Nürnberg, West Germany.

The problem of process synchronization in database systems is analyzed in a strictly systematic way, on a rather abstract level; the abstraction is chosen such that the essential characteristics of the problem can be distinctly modeled and investigated. Using a small set of concepts, a consistent description of the whole problem is developed; many widely used, but only vaguely defined, notions are defined exactly within this framework. The abstract treatment of the problem immediately leads to practically useful insights with respect to possible solutions, although implementational aspects are not discussed in detail.

A new approach to index organisation in inverted data bases, the filter organisation, is presented, which seems to be superior to classical organisations for a large class of applications. The general advantages of inverted data bases, namely fast retrieval and simple implementation of set theoretic operations, are preserved. Major improvements are obtained concerning storage requirements of the indexes and update behaviour. By the filter concept high stability of the whole index is obtained.

In parallel-accessed database systems a process must be able to lock a subset of the data. In current systems and proposals the only way for locking a set of data is either to lock explicitly each element in the set of to lock a large predefined set, such as a whole file. Though the necessity of a more flexible locking feature is recognised there are no results as to conceptual foundation and implementation. In this paper a concept for lock by value is developed which allows a process to lock a subset of the database just by specifying a condition describing this set. Thought the concept looks rather simple some unpleasant problems have to be discussed. A locking system supporting current lock features at the record-level as well as lock by value is proposed.