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Legacy Systems

Legacy Systems. An Introduction. Legacy Systems. Why do you think the agents are after his life ??. Legacy Systems. What is he doing hanging upside-down ?. What is he doing hanging upside-down ?. Objectives. To explain what is meant by a legacy system and why these systems are important

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Legacy Systems

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  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 ? What is he doing hanging upside-down ?

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

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

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

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- no consistent programming style • The system may use an obsolete programming language • The system documentation out-of-date • The system structure corrupted by many years of maintenance • Techniques to save space or increase speed at the expense of understandability may have been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

  8. The legacy dilemma • It is expensive and risky to replace the legacy system • It is expensive to maintain the legacy system • 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 B u s i n e s s p r o c e s s e s A p p l i c a t i o n s o f t w a r e S u p p o r t s o f t w a r e H a r d w a r e

  11. System change • In principle, it should be possible to replace a layer in the system leaving the other layers unchanged • In practice, this is usually impossible • Changing one layer introduces new facilities and higher level layers must then change to make use of these • Changing the software may slow it down so hardware changes are then required • 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 • The system may be file-based with incompatible files. The change required may be to move to a database-management system • In legacy systems that use a DBMS, the database management system may be obsolete and incompatible with other DBMS used by the business • 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 • Organisations that rely on legacy systems must choose a strategy for evolving these systems • Scrap the system completely and modify business processes so that it is no longer required • Continue maintaining the system • Transform the system by re-engineering to improve its maintainability • Replace the system with a new systems

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

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

  19. Why to Maintain Legacy Systems

  20. Current State of IBM Mainframe • Still home to between 70% to 80% of mission-critical legacy applications • 15-20% annual growth of installed processing capacity • Full integration of open computing and communications technologies • Number and types of applications spiraling • 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

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