A database design methodology is defined for the design of large relational databases. First, the data requirements are conceptualized using an extended entity-relationship model, with the extensions being additional semantics such as ternary relationships, optional relationships, and the generalization abstraction. The extended entity-relationship model is then decomposed according to a set of basic entity-relationship constructs, and these are transformed into candidate relations. A set of basic transformations has been developed for the three types of relations: entity relations, extended entity relations, and relationship relations. Candidate relations are further analyzed and modified to attain the highest degree of normalization desired. The methodology produces database designs that are not only accurate representations of reality, but flexible enough to accommodate future processing requirements. It also reduces the number of data dependencies that must be analyzed, using the extended ER model conceptualization, and maintains data integrity through normalization. This approach can be implemented manually or in a simple software package as long as a “good ” solution is acceptable and absolute optimality is not required.

We deal with directed hypergraphs as a tool to model and solve some classes of problems arising in Operations Research and in Computer Science. Concepts such as connectivity, paths and cuts are defined. An extension of the main duality results to a special class of hypergraphs is presented. Algorithms to perform visits of hypergraphs and to find optimal paths are studied in detail. Some applications arising in propositional logic, And-Or graphs, relational data bases and transportation analysis are presented. January 1990 Revised, October 1992 ( * ) This research has been supported in part by the "Comitato Nazionale Scienza e Tecnologia dell'Informazione", National Research Council of Italy, under Grant n.89.00208.12, and in part by research grants from the National Research Council of Canada. 1 Dipartimento di Informatica, Università di Pisa, Italy 2 Département d'Informatique et de Recherche Opérationnelle, Université de Montréal, Canada 2 INTRODUCTION Hypergraphs, a generaliz...

During its life a legacy system is subjected to many maintenance activities, which cause degradation of the quality of the system: when this degradation exceeds a critical threshold the legacy system needs to be reengineered. In order to preserve the asset represented by the legacy system, the familiarity with it gained by the system’s maintainers and users, and the continuity of execution of current operations during the reengineering process, the system needs to be reengineered gradually. Moreover, each program needs to be reengineered within a short period of time. The paper proposes a reengineering process model, which is applied to an in-use legacy system to confirm that the process satisfies previous requirements and to measure its effectiveness. The reengineered system replaced the legacy one to the satisfaction of all the stakeholders; the reengineering process also had a satisfactory impact on the quality of the system. Finally, this paper contributes to validate the cause-effect relationship between the reengineering process and overcoming the aging symptoms of a software system.

This study describes the application of a renewal process to a very old legacy system working in the banking environment. The term renewal process refers to a combination of reverse engineering and restoration processes. The latter, similar to restructuring but taking account of the semantics of the components to be restructured, is better explained in the paper. Judged from the maintainer's point of view, the main result of the case study described is that the renewal process renders the system easier to understand, so that the effort required to improve its quality can then be tailored to the benefits aimed at, even on a very old system. This case study had other spin-off benefits, providing guidelines for analyses to be made during the reverse engineering process in order to reduce the size of the system to be renewed and to extract the knowledge stored so as to understand and improve the existing application. It also made it possible to draw a distinction between the restoration pr...

There are many different types of information to be considered when designing an information system, and a wide variety of modelling approaches and notations (or representations) have been developed to describe these different types of information. Some types of information are better expressed by some representations than others, so it is sensible to use multiple representations to describe a real-world phenomenon. Reconciling and integrating descriptions expressed using different representations is therefore an important part of the design process. The objective of this research is to aid this reconciliation and integration within the context of information systems design. That is, to facilitate the use of multiple modelling representations for describing a phenomenon. To achieve this objective, the author has chosen an approach based upon translating descriptions of a phenomenon between different representations. This thesis provides several important contributions in the area of i...

Smith's method (Smith, 1985) is a formal technique for deriving a set of normalised relations from a functional dependency diagram (FDD). Smith's original rules for deriving these relations are incomplete, as they do not fully address the issue of determining the foreign key links between relations. In addition, one of the rules for deriving foreign keys can produce incorrect results, while the other rule is difficult to automate. In this paper are described solutions these issues.

This paper presents an iterative approach to database reengineering, starting from the assumption that for the user organization, the data are the most important asset in a legacy system. The most innovative feature of the proposed approach, in comparison with other rival approaches, is that it can eliminate all the ageing symptoms of the legacy data base. The new database can therefore be readily used to integrate data used by new functions introduced in the legacy software. Moreover, the approach allows all the services offered by modern data base management systems to be exploited. To test the effectiveness of the process described in this paper, it was experimented on a real legacy system; the results reported in the paper confirm its effectiveness. 1.

When modelling a real-world phenomenon, it can often be useful to have multiple descriptions of the phenomenon, each expressed using a different modelling approach or representation. Different representations such as entity-relationship modelling, data flow modelling and use case modelling allow analysts to describe different aspects of real-world phenomena, thus providing a more thorough understanding than if a single representation were used. Researchers working with multiple representations have approached the problem from many different fields, resulting in a diverse and potentially confusing set of terminologies. In this paper is described a viewpoint-based framework for discussing the use of multiple modelling representations to describe real-world phenomena. This framework provides a consistent and integrated terminology for researchers working with multiple representations.