Legacy SystemsLegacy SystemsAn Introduction

Legacy SystemsLegacy Systems

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Legacy SystemsLegacy Systems

What is he doing hanging upside-What is he doing hanging upside-down ?down ?

What is he doing hanging upside-What is he doing hanging upside-down ?down ?

ObjectivesObjectives 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

Legacy systemsLegacy systems Software systems that are developed speciallydeveloped specially

for an organisation

Many software systems that are still in use were developed many years ago using technologies that are now obsoletenow obsolete

These systems are still business criticalbusiness critical that is, they are essential for the normal functioning of the business

Hence, have been given the name LEGACY SYSTEMS

Legacy system Legacy system replacementreplacement

Legacy systems rarelyrarely have a complete specification - have undergone major changes

Business processes are reliantreliant on the legacy system

The system may embedembed business rules that are not formally documented elsewhere

New software development is riskyrisky and may not be successful

Legacy system changeLegacy system change Different parts & teams - no consistent no consistent

programming styleprogramming style The system may use an obsolete programming obsolete programming

languagelanguage The system documentation out-of-datedocumentation out-of-date The system structure corruptedstructure corrupted by many years

of maintenance Techniques to save space or increase speed at

the expense of understandabilityunderstandability may have been used

File structures used may be incompatibleincompatible

The legacy dilemmaThe 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.

Legacy system Legacy system componentscomponents

Systemhardware

Businessprocesses

Applicationsoftware

Business policiesand rules

Supportsoftware

Application data

ConstrainsUsesUsesRuns-onRuns-on

Embedsknowledge of

Uses

Layered modelLayered model

Hardware

Support software

Application software

Business processes

System changeSystem 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

File-based systemFile-based system

File 1 File 2 File 3 File 4 File 5 File 6

Program 2Program 1 Program 3

Program 4 Program 5 Program 6 Program 7

Database-centred systemDatabase-centred system

Program1

Program2

Program3

Program4

Databasemanagement

system

Logical andphysical

data models

describes

Transaction processingTransaction processing

Serialisedtransactions

Teleprocessingmonitor

Accountsdatabase

ATMs and terminals

Account queriesand updates

Legacy dataLegacy data The system may be file-basedfile-based with

incompatible files. The change required may be to move to a database-management system

In legacy systems that use a DBMS,DBMS, the database management system may be obsolete and incompatible with other DBMS used by the business

The teleprocessing monitorteleprocessing monitor may be designed for a particular DB and mainframe. Changing to a new DB may require a new TP monitor

Legacy system Legacy system assessmentassessment

Organisations that rely on legacy systems must choose a strategy for evolving these systems

ScrapScrap the system completely and modify business processes so that it is no longer required

Continue maintainingContinue maintaining the system

Transform the system by re-engineeringre-engineering to improve its maintainability

ReplaceReplace the system with a new systems

System quality & Business System quality & Business valuevalue

12

3 45

67

89

10

System quality

Business valueHigh business valueLow quality High business value

High quality

Low business valueLow quality

Low business valueHigh qualitySCRA

P

RE-ENGINEERMAINTAIN

REPLACE/MAINTAIN

Why to Maintain Legacy Why to Maintain Legacy SystemsSystems

Shortcomings of Client/Server Technology

Applications have not “scaledscaled” up well

Good securityGood security is difficult to achieve in a distributed environment

Total CostCost of Ownership has skyrocketed

Why to Maintain Legacy Why to Maintain Legacy SystemsSystems

Current State of IBM Current State of IBM MainframeMainframe

Still home to between 70% to 80% of mission-70% to 80% of mission-criticalcritical legacy applications

15-20% annual growth15-20% annual growth of installed processing capacity

Full integrationFull integration of open computing and communications technologies

Number and types of applications spiraling

Now the “Super ServerSuper Server” for distributed computing and Internet commerce

“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 Dale Vecchio, research analyst with Gartner GroupGroup

Thank YouThank You