Prototype databases are needed in any information system development process to support data-intensive applications development. It is common practice to populate these databases using synthetic data. This data usually bears little relation to the application's domain and considers only a very reduced subset of the integrity constraints the database will hold during operation. This paper claims that in situations where operational data is available, as is the case in information system evolution and migration, a sample of this data must be used to create a prototype database. The paper outlines a method for consistently sampling a database. This method uses a new concept, the Insertions Chain Graph, to assist in selecting instances so that the resulting Sample Database reaches a consistent state, a significant task of database sampling.

One of the most difficult challenges arising from dealing with so called legacy systems is how to identify and determine the 'legacy status' of such a system, where no commonly accepted definitions existed until very recently. This paper tackles this problem. It researches into the concept of legacy status and related issues, and aims at developing a set of frameworks and an associated technique, which can be used by management to identify legacy status accurately in a current or a planned business information system. This paper first presents a definition of the concept of 'legacy status' with a 3-dimensional model. It then discusses the LACE frameworks and technique, which can be used to assess legacy status from the cause and effects' perspectives. It also outlines a method for applying these LACE frameworks and the technique with a mathematical model and metric so that the legacy status of a legacy system can be calculated. This paper describes a novel and practical way to identify legacy status of an information system, and has possibly pointed out a new direction for research in this area.

The widespread use of computer technology over several decades has resulted in some large, complex systems that have evolved to a state where they significantly resist further modification and evolution. Although these Legacy Information Systems pose considerable problems (brittleness, inflexibility, isolation, non-extensibility, lack of openness, etc.), they may also be mission-critical: if one of these systems stops working the business may grind to a halt. Thus for many organisations, decommissioning is not an option. An alternative solution is Legacy System Migration that has recently become an important research and practical issue. Legacy System Migration is a relatively new field of research and few comprehensive methods or practical experiences have been reported. This paper provides a brief overview of existing research and practise when dealing with Legacy Information Systems, and in particular of the area of Legacy Information System Migration.

A legacy information system represents a massive, long-term business investment. Unfortunately, such systems are often brittle, slow and non-extensible. Capturing legacy system data in a way that can support organizations into the future is an important but relatively new research area. The authors offer an overview of existing research and present two promising methodologies for legacy information system migration.

The problems posed by mission-critical legacy systems-e.g., brittleness, inflexibility, isolation, non-extensibility, lack of openness-are well known, but practical solutions have been slow to emerge. Generally, organisations attempt to keep their legacy systems operational, while developing mechanisms which allow the legacy systems to interoperate with new, modern systems which provide additional functionality. The most mature approach employs gateways to provide this interoperability. However, gateways introduce considerable complexity in their attempt to maintain consistency between the legacy and target systems. This paper presents an innovative gateway-free approach to migrating legacy information systems in a mission-critical environment: the Butterfly Methodology. The fundamental premise of this methodology is to question the need for the parallel operation of the legacy and target systems during migration.

The widespread use of computer technology over several decades has resulted in some large, complex systems which have evolved to a state where they significantly resist further modification and evolution. These Legacy Information Systems are normally mission-critical : if one of these systems stops working the business may grind to a halt. Thus for many organisations, decommissioning is not an option. An alternative solution is Legacy System Migration which has recently become an important research and practical issue. This paper presents an approach to mission-critical legacy systems migration: Butterfly methodology. Data migration is the primary focus of Butterfly methodology, however, it is placed in the overall context of a complete legacy system migration.

• the systems cannot evolve to provide new functionalities required by the organisation • they run on obsolete hardware which is expensive to maintain and reduces productivity due to the low speed of the old hardware • maintenance is expensive, tracing failures is costly and time consuming due to the lack of documentation and a general lack of understanding of the internal workings • integration efforts are greatly hampered by the absence of clean interfaces

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The problems posed by mission-critical legacy systems: brittleness, inflexibility, isolation, non-extensibility, lack of openness etc., are well known, but practical solutions have been slow to emerge. Most approaches are "ad hoc" and tailored to peculiarities of individual systems. This paper presents an approach to mission-critical legacy system migration: the Butterfly methodology, its data migration engine and supporting toolkit framework. Data migration is the primary focus of the Butterfly methodology, however, it is placed in the overall context of a complete legacy system migration. The fundamental premise of the Butterfly methodology is to question the need for parallel operation of the legacy and target systems during migration. Much of the complexity of the current migration methodologies is eliminated by removing this interoperation assumption.