Legacy

Legacy Information Systems: Issues and Directions

Bisbal, J.; Lawless, D.; Bing Wu; Grimson, J.

Jesus.Bisbal@cs.tcd.ie

Term Paper Done by Tay Pei Fang (S11)





Abstract

A Legacy information system represents a 2.3 User Interface

massive, long-term business investment. User Interface is the main access to the

Unfortunately, such systems are often brittle, function of the software system. For most

slow, and non-extensible. Capturing legacy legacy systems, they usually have character-

system data in a way that can support based or command interfaces, which are

organizations into the future is an important but very complex and needs a long time to learn.

relatively new research area. The authors offer Reengineering these interfaces to make

an overview of existing research and present them more users friendly would extend the

two promising methodologies for legacy life of these legacy systems.

information system migration.

3 New Contribution to Software Engineering

Keywords

Legacy systems, reverse engineering,  New ways of managing the legacy systems

redevelopment, wrapping, migration, “Chicken have emerge due to the high maintenance

Little Strategy”, “Butterfly Methodology” cost and also the appearance of cheaper

and more flexible alternatives such as the

1 Introduction COTS.



Legacy Information Systems was written years  Different types of reengineering the legacy

ago using outdated techniques, yet many are systems, such as Reverse Engineering, and

still mission critical and have a great impact on Forward Engineering have also slowing

business. These systems usually run on becoming a continuing part of the process of

obsolete hardware. They are usually very software development and evolution.

difficult and expensive to maintain in both

hardware and software. Legacy systems may  New LIS migration methodologies, which

represent the years of accumulated experience offer more flexibility, better system

and knowledge. Thus it is not easy to upgrade understanding, easier maintenance and

and migrate several hundred programs and reduced costs.

databases without disrupting data-processing

services. With all these methods and solutions emerging

to take care of the legacy systems, maintenance

2 Topics Related in Lecture cost and efforts and systems failures will

gradually decreased. Thus offering long-term

2.1 Commercial Of The Shelf (COTS) benefits.

It discusses how COTS can be constructed

from the existing computing units embedded As a result there will be more business

in the legacy information systems. The opportunities, which in turn, leads to the

existing legacy systems embody a collection increase of the company and system’s values.

of large properties of algorithms and

functions, which could be reusable in new 4 Techniques Discussed in the Article

systems development. Legacy application

systems, particularly some of their functions, This article basically discussed about the basic

are too valuable to be discarded and too problems and several solutions to Legacy

expensive to reproduce (Bennett 1995). Information Systems (LIS). Legacy Information

Systems usually run on obsolete hardware that

2.2 Software Maintenance is difficult and expensive to maintain. Software

Preventing system performance from maintenance is also expensive due to the lack of

degrading to unacceptable level and understanding of the system. LIS usually have

maintaining controls over the modifications poor interfaces that are difficult to use and

made to the system are especially needed in integrate with other systems. Furthermore, they

LIS. This is because the designs to those are difficult to extend.

systems are usually using ad-hoc solutions,

which would make the maintenance and There are three ways to overcome the problems

testing very difficult in the long run. and they are redevelopment, wrapping and







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migration. Based on the complexity and risk of information system. With the interoperation of

failure in LIS projects, wrapping is considered as both the systems, the process could be complex

a short-term solution and it can complicate the and slow.

LIS maintenance over a long term.

Redevelopment on the other hand is far too risky As for the Butterfly Methodology, it assumes that

for most organization but this provides a long- although the LIS must remain operable

term plan. As for migration, it is a middle ground throughout migration, the LIS and target system

by providing a long-term solution while mitigating need not interoperate during the process.

the risk of system shutdown.

It is basically like a parallel run where both the

There are two migration methods discussed in LIS and target system are run at the same time

the article. These two approaches are the after the legacy databases are transfer over to

“Chicken Little Strategy” and the “Butterfly the target database. However, any transactions

Methodology”. The first approach, “Chicken during the transfer are logged in temporary

Little Strategy”, lets the LIS and target systems tables. This table will be transfer to the target

interoperate during migration using a mediating database later. During the transfer of the

module. This strategy rebuilt the LIS applications temporary tables, any further manipulations of

gradually on the target system. The target the data are stored in another temporary tables.

system is initially quite small but it grows as the This iteration would go on until the last temporary

migration progresses. This method starts with tables reaches a stage where the migration of

the analysis of the LIS followed by the designing these last tables would not cause any serious

of the target interface, database and application. inconvenience to the core business.

It will then start to migrate the legacy databases

and finally leads to the cut over to the target



5 Related work that has been published

Author(s) Year Article Description How does it relate to

your main article

Keith Bennett 1995 Legacy Systems:  Discuss the alternatives and  It describe in details

Coping with solutions to legacy systems. how legacy systems

Success  Demonstrate the progress made comes about and why

in managing legacy systems. there is a need to come

 Legacy dilemma on whether to out with new ways or

trade off the cost of continuing to solution to extend the

cope with the legacy system life of legacy system.

against the investment needed to  Main article is

improve it and the benefit of describing 2 of the

easier subsequent maintenance. methodologies that

helps in extending the

life of legacy systems



Harry M. Sneed 1995 Planning the  Issues and efforts to consider  Extending on the idea of

reengineering of before the start of transforming migration

Legacy Systems the legacy systems.  Issues of legacy

 Steps on the reengineering systems

process of the Legacy system  Before addressing the

 Different definition of problems of the legacy

reengineering to different people. systems, a thorough

E.g. Business reengineering and analysis of the legacy

Software reengineering. BR will systems is needed on

only indirectly affect the software the cost, benefits and

but SR involves the renovation of project justifications of

programs, procedures and data the systems. These are

structure etc. parts of the

reengineering process

discuss in both article.

 The objectives of both

the articles are to

improve the

maintainability and

reliability of the system.









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Ettore Merlo, Pierre- 1995 Reengineering  The article describes how the  Extending on the idea of

Yves Gagne, Jean- User Interfaces process of turning a character- interface reengineering

Francois Girad, based interface into a graphical or migration

Kostaas on can be partially automated.  The advantages of

Kontogiannis, Laurie  This partially automated reengineer the

Hendren, Prakasb approach separates the interface interfaces (extend the

Panangaden, and and application code, so that new life of legacy system

Renato De Mori interface code for a system can etc.).

be generated without modifying

the old.



T.Skarmstad, Md. 1999 Constructing  How COTS can be constructed  Extending on the idea of

Khaled Khan, Md. Commercial Off- from the existing computing units interface reengineering

Abdur Rashid the-Shelf from embedded in the legacy  Discuss a similar

Legacy Systems: information systems. approach of migration

A Conceptual  Describe the steps in reverse

Framework engineering or migrating

 Describe the steps for Wrapping

a system









6 Relation of Techniques to Lab Project  How certain technologies have emerge due to

the legacy systems. E.g. Web technologies

Basically this technique is not related to my project

on implementing a new ticketing system for LRT in  Approaches to “freeze” and encapsulate the

NTU. This is because, my project is a non-existing legacy system as a component in a new

system. We have to base on the client implementation. E.g. Controls over the

specifications to develop the system instead of modifications made to the system

analyzing from an existing old system. In this

case, redevelopment, wrapping and migration

does not comes into the picture. Furthermore, my

system does not require a database and thus 8 Comments on Notations/Diagrams

migration of database and applications are not

applicable also. 8.1 Complex diagrams

It is more suitable for readers with certain

How these articles help in Lab Project knowledge or experience in the transformation

of huge Legacy systems. It should provide a

It serves as a reminder to us that the analyzing more general diagram for the approaches

and designing stage is much more important than discuss in the article on top of the in-depth

coding stage. This is because today’s successful diagrams for novice readers.

software systems are still likely to turn into

tomorrow’s legacy system. In order to reduce

maintenance cost and enhance reusability and 8.2 Content Well Organized

easy future add on to the system, it is best to do a It first gave an overview of what is a legacy

good design which is reusable and easy to system followed by the needs to redevelop or

maintain rather than going straight into coding reengineer the system. It then illustrates and

staging with careful analysis of the requirements. discusses the solution to the legacy systems

and also gave the cost and evaluation for each

7 Extension to Article solution. After the introduction, it then

describes in details how the 2 migration

 Differentiate the types of reengineering methods works. Lastly, it rounds up by

methods and evaluates on each methods. summarizing the needs for LIS migration.



 Determine the implications, cost and benefits 8.3 Explanation Clear and easy to understand

of transforming the legacy systems. The article does not use bombastic words or

jargons. It is easy for reader with novice level

 Compare the solutions for short-term benefits of software engineering.

to long-term benefits in terms of effort, time

taken and cost for maintenance.









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9 Validation and Expansion to Article had spent millions of dollars fixing the problem.

Therefore, those solutions or methods

The 2 methods discuss in the article are meant for mentioned in the articles are definitely needed

huge legacy systems which are time critical and to solve this problem. These companies may

transactions intensive. We can also use the 2 have either redeveloped a new system or just

methods for smaller legacy systems. In this case patched up the database depending on the

the database would not be so huge and the time both the financial, urgency and system life

taken to transfer it would be much shorter than factors.

those big system.

11.2 Relevance to immediate future

For example, a huge Legacy system like the bank Beside the Y2K problem, there are still a lot

financial systems using mainframe and more legacy problems. Furthermore today’s

unstructured COBOL would required the “Butterfly successful software systems still have the

method” by transfer the database and application tendency to turn into tomorrow’s legacy

to the target system gradually. system. Therefore, there is not only a need to

capture the legacy system data in such a way

For a small legacy system such as accounting that it can support organizations into the future,

packages for e.g. NTU Alumini Club, it is not so there is also a need for more ways to manage

time critical and the number of transactions is a system to prevent it from degrading.

minimal as compare to the bank systems.

Therefore, the butterfly method can be hasten up Besides solving legacy problems, the two

by selecting a time e.g. 3am in the morning when methods discussed in the article can also be

the club is not in operation to transfer the used for example in the merger of banks or

database. In this way, all the necessary data can financial institutions where there is a need to

be transferred to the target database at one go. study the systems in details and redraft on the

There is no need to synchronize the database business policies. In this case, these

further and it also will not affect the operation of organizations will needs to either migration the

the club. Although the database is transfer over, database from one to another or have a new

the legacy system is not cut off immediately. system and database to be able to cater to all

Usually a parallel of at least 2 months is needed to the different business policies.

test the target system. The whole operation will

only be cut over when the target system is stable Thus a further research into this area will

and functioning correctly. In this way, the definitely prove to be of great contributions to

migration is then considered successful. the society.





10 Comments on the S/W Project, Process, 12 References

Platform, People & Product of the Article

1. T.Skarmstad, Md. Khaled Khan, Md. Abdur

This article describes the solutions to the legacy Rashid (1999). Constructing Commercial Off-

systems in a very general way where it may not be the-Shelf from Legacy Systems: A Conceptual

suitable for certain platform, application or Framework [World Wide Web page]. Available:

software. It should give a guideline on which type

more sophisticated each day, it will be even more

difficult to migrate a system. It should not only 2. N.Serbedzijia (2000). Engineering Web

discuss the methods on migrating systems and Technologies for Legacy Systems [World Wide

database but also some ways of maintaining and Web page]. Available:

curing.

3. M.Bieber (1998). Web Engineering [World

11 Comments Wide Web page]. Available:

11.1 Results

Legacy problems have already exists for 4. S.Santhanakrishnan (2001). Re-Engineering

several decades and one the most significant Legacy Applications [World Wide Web page].

problem is the Y2K bug. Many big companies Available:



5. D. O’ Sullivan, R. Richardson. Applications of

Case Based Reasoning to Legacy System

Migration [World Wide Web page]. Available:



6. B. Wu et al. (1997) The butterfly Methodology:

A Gateway-Free Approach for Migrating

Legacy Information Systems, IEEE Computer

Soc. Press, Los Alamitos, Calif









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