1. Legacy Systems An Introduction

2. Legacy Systems Why do you think the agents are after his life ??

3. Legacy Systems What is he doing hanging upside-down ?

4. Objectives l To explain what is meant by a legacy system and why these systems are important l To introduce common legacy system structures l To explain how the value of legacy systems can be assessed

5. Legacy systems developed specially l Software systems that are developed specially for an organisation now obsolete l Many software systems that are still in use were developed many years ago using technologies that are now obsolete business critical l These systems are still business critical that is, they are essential for the normal functioning of the business l Hence, have been given the name LEGACY SYSTEMS

6. Legacy system replacement rarely l Legacy systems rarely have a complete specification - have undergone major changes reliant l Business processes are reliant on the legacy system embed l The system may embed business rules that are not formally documented elsewhere risky l New software development is risky and may not be successful

7. Legacy system change no consistent programming style l Different parts & teams - no consistent programming style obsolete programming language l The system may use an obsolete programming language documentation out-of-date l The system documentation out-of-date structure corrupted l The system structure corrupted by many years of maintenance understandability l Techniques to save space or increase speed at the expense of understandability may have been used incompatible l File structures used may be incompatible

8. The legacy dilemma l It is expensive and risky to replace the legacy system l It is expensive to maintain the legacy system l Businesses must weigh up the costs and risks and may choose to extend the system lifetime using techniques such as re- engineering.

9. Legacy system components

10. Layered model Hardware Support software Application software Business processes

11. System change l In principle, it should be possible to replace a layer in the system leaving the other layers unchanged l In practice, this is usually impossible l Changing one layer introduces new facilities and higher level layers must then change to make use of these l Changing the software may slow it down so hardware changes are then required l It is often impossible to maintain hardware interfaces because of the wide gap between mainframes and client- server systems

12. File-based system

13. Database-centred system

14. Transaction processing

15. Legacy data file-based l The system may be file-based with incompatible files. The change required may be to move to a database-management system DBMS, l In legacy systems that use a DBMS, the database management system may be obsolete and incompatible with other DBMS used by the business teleprocessing monitor l The teleprocessing monitor may be designed for a particular DB and mainframe. Changing to a new DB may require a new TP monitor

16. Legacy system assessment l Organisations that rely on legacy systems must choose a strategy for evolving these systems l Scrap l Scrap the system completely and modify business processes so that it is no longer required l Continue maintaining l Continue maintaining the system re-engineering l Transform the system by re-engineering to improve its maintainability l Replace l Replace the system with a new systems

17. System quality & Business value SCRAP RE-ENGINEER MAINTAIN REPLACE/ MAINTAIN

18. Why to Maintain Legacy Systems l Shortcomings of Client/Server Technology scaled l Applications have not “scaled” up well l Good security l Good security is difficult to achieve in a distributed environment Cost l Total Cost of Ownership has skyrocketed

19. Why to Maintain Legacy Systems

20. Current State of IBM Mainframe 70% to 80% of mission-critical l Still home to between 70% to 80% of mission-critical legacy applications l 15-20% annual growth l 15-20% annual growth of installed processing capacity l Full integration l Full integration of open computing and communications technologies l Number and types of applications spiraling Super Server l Now the “Super Server” for distributed computing and Internet commerce

21. “Organizations should no longer think of S/390 as synonymous with MVS and legacy application paradigms. Through the incorporation of open industry standards such as HTML, HTTP, XML and J2EE-compliant Java technology, new e- business applications and transactions can now be developed for deployment on this platform.” Dale Vecchio, research analyst with Gartner Group

22. Thank You