Legacy Systems An Introduction. Legacy Systems Why do you think the agents are after his life ??
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Legacy SystemsLegacy SystemsAn Introduction
Legacy SystemsLegacy Systems
Why do Why do you think you think the the agents agents are after are after his life ??his life ??
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languagelanguage The system documentation out-of-datedocumentation out-of-date The system structure corruptedstructure corrupted by many years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
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