SWEN 256 – Software Process & Project Management

Software change is inevitable

o New requirements emerge when the software is under

development or being used

o The business environment changes

o Errors must be repaired, Risks mitigated

o New equipment must be accommodated

o The performance or reliability may have to be improved

A key problem for organisations is implementing

and managing change to their current projects and

legacy systems

Sometimes change occurs during development

that necessitates changes in scope o Approval of CCB (Change Control Board) and

o Requires extensive planning

o May require more time/resources (project triangle)

Plan-driven methodologies may or may not have this built in

(i.e. Spiral) or may be specifically built to resist change (i.e.

Waterfall)

Agile Methodologies embrace change

o Scrum allows for change to the Product Backlog at any time, but

manages risk by freezing the current Sprint Backlog

Stakeholder Communication IS KEY

Software maintenance

o Changes are made in response to changed requirements

but the fundamental software structure is stable

Architectural transformation

o The architecture of the system is modified generally from

a centralised architecture to a distributed architecture

Software re-engineering

o No new functionality is added to the system but it is

restructured and reorganised to facilitate future changes

These strategies may be applied separately or

together

Law Description

Cont inuing change A program that is used in a real-world environment

neces sarily must change or become progress ively less

useful in that environment.

Increasing complexity As an evolving program changes , its st ructure tends

to become more complex. Extra res ources must be

devoted to pres erving and simplifying the s tructure.

Large program evolut ion Program evolution is a s elf-regulating process .

Syst em att ributes such as size, time between releas es

and the number of reported errors are approximately

invariant for each s ystem release.

Organis ational st ability Over a program’s lifet ime, its rate of development is

approximately const ant and independent of the

resources devoted to sys tem development.

Cons ervation of

familiarit y

Over the lifetime of a sys tem, the incremental change

in each releas e is approximately constant.

This has not yet been established

They are generally applicable to large, tailored

systems developed by large organisations

It is not clear how they should be modified for

o Shrink-wrapped software products

o Systems that incorporate a significant number of COTS

components

o Small organisations

o Medium sized systems

Modifying a program after it has been put into

use

Maintenance does not normally involve major

changes to the system’s architecture

Changes are implemented by modifying existing

components and adding new components to the

system

The system requirements are likely to change

while the system is being developed because

the environment is changing. Therefore a

delivered system won't meet its requirements!

Systems are tightly coupled with their environment.

When a system is installed in an

environment it changes that environment and

therefore changes the system requirements.

Systems MUST be maintained therefore if they

are to remain useful in an environment

Maintenance to repair software faults

o Changing a system to correct deficiencies in the way meets

its requirements (Corrective Maintenance)

Maintenance to adapt software to a different operating

environment

o Changing a system so that it operates in a different environment

(computer, OS, etc.) from its initial implementation (Adaptive

Maintenance)

Maintenance to add to or modify the system’s functionality

o Modifying the system to satisfy new requirements (Perfective

Maintenance)

F u nc t io na li ty

a dd it io n or

m o di fi c a ti on

(65 % )

F a u lt re pa i r

(17 % )

S o f tw are

a da p ta t io n

(18 % )

S p e ci f ic a t io n Im pl e m e nt io n

V a li da t io nO p e ra ti on

S ta rt

R e le as e 1

R e le as e 2

R e le as e 3

Usually greater than development costs (2* to

100* depending on the application)

Affected by both technical and non-technical

factors

Increases as software is maintained.

Maintenance corrupts the software structure so

makes further maintenance more difficult.

Ageing software can have high support costs

(e.g. old languages, compilers etc.)

0 5 0 1 00 1 50 2 00 2 50 3 00 3 50 4 00 4 50 5 00

S y st e m 1

S y st e m 2

D e v e lo pm e n t c os ts M a in te n a nc e c os ts

$

Team stability

o Maintenance costs are reduced if the same staff are involved with

them for some time

Contractual responsibility

o The developers of a system may have no contractual responsibility

for maintenance so there is no incentive to design for future change

Staff skills

o Maintenance staff are often inexperienced and have limited domain

knowledge

Program age and structure

o As programs age, their structure is degraded and they become

harder to understand and change

Rather than think of separate development and

maintenance phases, evolutionary software is

software that is designed so that it can

continuously evolve throughout its lifetime

YES, but how/much?

Maintenance prediction is concerned with

assessing which parts of the system may cause

problems and have high maintenance costs

o Change acceptance depends on the maintainability of

the components affected by the change

o Implementing changes degrades the system and

reduces its maintainability

o Maintenance costs depend on the number of changes

and costs of change depend on maintainability

P re di c ti ng

m a in ta i na b il it y

P re di c ti ng sy st e m

c ha n ge s

P re di c ti ng

m a in te n a nc e

c os ts

W h a t w i ll be th e li fe ti m e

m a in te n a nc e c os ts of th is

s ys te m ?

W h a t w i ll be th e c os ts o f

m a in ta i ni ng t hi s s ys t em

o ve r t he n e xt y e a r?

W h a t pa r t s o f t he s ys te m

w i ll be t he m os t e x pe ns iv e

t o m a i nt a in ?

H o w m a ny c ha n ge

re qu e st s c a n b e

e xp e c te d ?

W h a t pa r ts o f the sy ste m a re

m os t li ke ly t o b e a f fe c te d by

c ha n ge re qu e st s?

Predicting the number of changes requires an

understanding of the relationships between a

system and its environment

Tightly coupled systems require changes whenever

the environment is changed

Factors influencing this relationship are

o Number and complexity of system interfaces

o Number of inherently volatile system requirements

o The business processes where the system is used

Predictions of maintainability can be made by

assessing the complexity of system components

Studies have shown that most maintenance effort

is spent on a relatively small number of system

components

Complexity depends on

o Complexity of control structures

o Complexity of data structures

o Procedure and module size

Process measurements may be used to assess

maintainability

o Number of requests for corrective maintenance

o Average time required for impact analysis

o Average time taken to implement a change request

o Number of outstanding change requests

If any or all of these is increasing, this may indicate

a decline in maintainability

There is a need to convert many legacy systems

from a centralised architecture to a client-server

architecture

Change drivers

o Hardware costs. Servers are cheaper than mainframes

o User interface expectations. Users expect graphical user

interfaces (CLIGUI)

o Distributed access to systems. Users wish to access the

system from different, geographically separated,

computers

Factor Description

Business importance Returns on the investment of distributing a legacy system depend on its

importance to the business and how long it will remain important. If

distribution provides more efficient support for stable business

processes then it is more likely to be a cost-effective evolution strategy.

System age The older the system the more difficult it will be to modify its

architecture because previous changes will have degraded the structure of

the system.

System structure The more modular the system, the easier it will be to change the

architecture. If the application logic, the data management and the user

interface of the system are closely intertwined, it will be difficult to

separate functions for migration.

Hardware procurement

policies

Application distribution may be necessary if there is company policy to

replace expensive mainframe computers with cheaper servers. .

Ideally, for distribution, there should be a clear

separation between the user interface, the system

services and the system data management

In practice, these are usually intermingled in older

legacy systems

D a t a ba s e

U s e r i nt e r fa c e

S e rvi c e s

Ide a l m o de l for di st r ib ut io n R e a l le g a c y s ys te m s

D a t a ba s e

U s e r i nt e r fa c e

S e rvi c e s

St ra tegy A dva nt age s D is adva nt age s

Imp lem e nta t ion

u s ing th e w indow

m a nage m ent

s ys tem

A cc e ss to a ll UI f unc t ion s so no

re a l re s tri ct ions on UI de s ign

Be t te r UI pe rf o rm ance

P la tf o rm dep e ndent

M ay be m o re di ffi cul t to ach ieve

in te rf a c e con s is te ncy

Imp lem e nta t ion

u s ing a w eb

b ro w ser

P la tf o rm ind e penden t

Lo w e r tr ain ing co s ts due to u s e r

fa m il ia r ity w i th th e WWW

E a sie r to a chi e ve int erf ac e

con s is te ncy

P oten t ia l ly poo re r UI

pe rf o rm anc e

Int erf ac e des ign i s con s tra ined

by th e f ac i li t ie s p rovid e d by web

b ro w ser s

The costs of software change usually exceed the

costs of software development

Factors influencing maintenance costs include

staff stability, the nature of the development

contract, skill shortages and degraded system

structure

Architectural evolution is concerned with evolving

centralised to distributed architectures

A distributed user interface can be supported using

screen management middleware