maintanance 2 (1)

7/28/2019 Maintanance 2 (1)

1/37

2004 by SEC

Software Maintenance


2/37

2

2004 by SEC

Software Evolution

It is impossible to produce system of any size which do notneed to be changed. Once software is put into use, newrequirements emerge and existing requirements changes as the

business running that software changes.

Parts of the software may have to be modified to correcterrors that are found in operation, improve its performance orother non-functional characteristics.

All of this means that, after delivery, software systems always

evolve in response to demand for change.


3/37

3

2004 by SEC

Software Maintenance

Software maintenance is the general process of changing asystem after it has been diverted.

The change may be simple changes to correct coding errors,more extensive changes to correct design errors or significantenhancement to correct specification error or accommodatenew requirements.


4/37

4

2004 by SEC

Maintenance Characteristics

We need to look at maintenance from three differentviewpoints: [PRE2004]

the activities required to accomplish the maintenance phase and the

impact of a software engineering approach (or lack thereof) on theusefulness of such activities

the costs associated with the maintenance phase

the problems that are frequently encountered when softwaremaintenance is undertaken


5/37

5

2004 by SEC

Computer software programmers and engineers perform

various software maintenance functions to keep software

running with as few problems as possible.

Programmers and engineers also constantly seek to improvethe reliability and functionality of software through

maintenance activities.

Many businesses rely on various software programs to

manage their finances, inventory, employees, securitysystems, and other facets of business activity.

Types of Maintenance


6/37

6

2004 by SEC

Corrective software maintenance involves developing and

deploying solutions to problems ("bugs") that arise during use

of a software program.

Computer users will notice performance problems withsoftware, such as error messages coming on the screen or the

program freezing or crashing, meaning corrective software

maintenance is needed.

Often these fixes permanently solve the problem, but not

always. Some fixes act as a temporary solution while computer

programmers work on a more permanent solution.

Corrective


7/37

7

2004 by SEC

Perfective

No software program contains zero flaws or areas

for improvement. Perfective software maintenance

involves computer programmers working to improve

the way a software program functions or how

quickly it processes requests. Programmers may also

engage in perfective


8/37

8

2004 by SEC

software maintenance to improve the software's

menu layouts and command interfaces. Sometimes

programmers need to conduct perfective

maintenance on software because of outside

influences, such as new government regulations that

affect how a business operates.

Perfective(contd)


9/37

9

2004 by SEC

Adaptive

The field of technology constantly changes through bothhardware and software developments. Adaptive softwaremaintenance addresses these changes. A change in a

processor's speed, for example, will affect how the softwareperforms on a single computer. Software interacts with othersoftware programs on a computer or network, meaningchanges in one program can require changes in other

programs. A user will eventually introduce new software tothe computer or network, which can also affect how other

software already present operates.


10/37

10

2004 by SEC

Preventative

When computer programmers engage in preventative softwaremaintenance they try to prevent problems with software

programs before they occur. Programmers seek to preventcorrective maintenance as much as possible, while alsoanticipating adaptive maintenance needs before usersexperience problems. Computer programmers test software, asautomotive companies test the vehicles they make, to makesure the software can handle high data loads and otherstressful operations without problems. Computer

programmers also test the software with other programs userslikely will use on their computers, making sure compatibilityissues do not arise.


11/37

11

2004 by SEC

Maintenance effort distribution .[SOM2004]

software

adaption

(18%)

Fault repair

(17%)

functionality

addition ormodification

(65%)


12/37


13/37

13

2004 by SEC

Maintenance Examples

Y2K

many, many systems had to be updated

language analyzers (find where changes need to be made)

Anti-Virus Software

don't usually have to update software, but must send virus definitions


14/37

14

2004 by SEC

Maintenance Examples (contd)

Operating System Patching

Microsoft, Apple, Linux/Unix

OS is core to use of computer, so it must be constantly maintained

Commercial Software in General

customers need to be informed of updates

updates have to be easily available - web is good tool


15/37

15

2004 by SEC

Usually greater than development costs (2* to100* depending on the application)

Affected by both technical and non-technicalfactors

Increases as software is maintained.Maintenance corrupts the software structure somakes further maintenance more difficult.

Ageing software can have high support costs

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

Maintenance Costs


16/37

16

2004 by SEC

Maintenance Costs (contd)

Time and money (software that costs 10 a line to develop costs 400 aline to maintain)

Organizations become maintenance bound and cannot produce new

software Customer dissatisfaction when seemingly legitimate requests for repair or

modification cannot be addressed in a timely manner

Reduction in overall software quality as changes introduce latent errors inthe maintained software

Upheaval caused during development efforts when staff must be pulledto work on a maintenance task


17/37

17

2004 by SEC

Team stability

Maintenance costs are reduced if the same staff are involved withthem for some time

Contractual responsibility

The developers of a system may have no contractual responsibilityfor maintenance so there is no incentive to design for future change

Staff skills

Maintenance staff are often inexperienced and have limited domain

knowledge

Program age and structure

As programs age, their structure is degraded and they becomeharder to understand and change

Maintenance Cost Factors


18/37

18

2004 by SEC

Maintainability Factors

Availability of qualified staff.

Understandable system structure.

Use of standardized programming languages

and operating systems. Standardized structure of documentation.

Availability of test cases.

Built-in debugging facilities.

Availability of a proper computer to conductmaintenance.


19/37

19

2004 by SEC

Maintenance Side Effects

In this context a side effect implies an error or undesirablebehavior that occurs as the result of a modification.

the three major areas are[PRE2004]

code

data structures

documentation


20/37

20

2004 by SEC

Documentation Side Effects

These consist of the failure to update documentation so that itno longer matches the code.

If the user doesnt know about changes frustration is

inevitable.

The entire documentation should be reviewed before re-release


21/37

21

2004 by SEC

Coding Side Effects

Any change can cause side-effects but these tend to be moreerror prone a subprogram is deleted or changed

A statement label is deleted or modified

An identifier is deleted or modified

Changes are made to improve execution performance


22/37

22

2004 by SEC

Coding Side Effects (contd)

Logical operators are modified

Files are opened or closed

Design changes which translate into major code changes Changes are made to logical tests of boundary conditions

These may be caught in testing or cause software failureduring operation.


23/37

23

2004 by SEC

Data Side Effects

Data side effects occur as the result of modifications made toa data structure. The most error-prone are:

redefinition of local and global constants

redefinition of record or file formats

Incr. or decr. in size of array or other data structure

modification of global data

re initialization of control flags and pointers

rearrangements of parameters (especially in I/O)


24/37

24

2004 by SEC

Re-engineering, Reverse Engineering

and Forward Engineering,


25/37

25

2004 by SEC

Software Rejuvenation

Re-documentation

Creation or revision of alternative representations of software

at the same level of abstraction

Generates:

data interface tables, call graphs, component/variable crossreferences etc.

Restructuring

transformation of the systems code without changing its behavior


26/37

26

2004 by SEC

Software Rejuvenation (contd)

Reverse Engineering

Analyzing a system to extract information about the behavior and/orstructure

also Design Recovery - recreation of design abstractions from

code, documentation, and domain knowledge Generates:

structure charts, entity relationship diagrams, DFDs, requirementsmodels

Re-engineering

Examination and alteration of a system to reconstitute it in anotherform

Also known as renovation, reclamation


27/37

27

2004 by SEC

Re-structuring or re-writing part or all of alegacy system without changing itsfunctionality

Applicable where some but not all sub-systems

of a larger system require frequentmaintenance

Re-engineering involves adding effort to makethem easier to maintain. The system may be re-structuredand re-documented

System Re-engineering


28/37

28

2004 by SEC

When system changes are mostly confined topart of the system then re-engineer that part

When hardware or software support becomesobsolete

When tools to support re-structuring areavailable

When to Re-engineer


29/37

29

2004 by SEC

Re-engineering Advantages

Reduced risk

There is a high risk in new software development. There may bedevelopment problems, staffing problems and specification

problems

Reduced cost The cost of re-engineering is often significantly less than the costs

of developing new software


30/37

30

2004 by SEC

Forward Engineering and Re-engineering [SOM2004]

Understanding andtransformation

Existingsoftware system

Re-engineeredsystem

Design andimplementation

Systemspecification

Newsystem

Software re-engineering

Forward engineering


31/37

31

2004 by SEC

Re-Engineering Cost Factors

The quality of the software to be re-engineered

The tool support available for re-engineering

The extent of the data conversion which is required

The availability of expert staff for re-engineering


32/37

32

2004 by SEC

Re-Engineering Approaches[SOM2004]

Automated r estructuringwith manual changes

Automated sourcecode conversion

Restructuring plusarchitectural changes

Automated programrestructuring

Program and datarestructuring

Increased cost


33/37

33

2004 by SEC

Source Code Translation

Involves converting the code from one language (orlanguage version) to another e.g. FORTRAN to C

May be necessary because of:

Hardware platform update

Staff skill shortages

Organisational policy changes

Only realistic if an automatic translator is available


34/37

34

2004 by SEC

The Program Translation Process[SOM2004]

Automaticallytranslate code

Design translatorinstructions

Identify sourcecode differences

Manuallytranslate code

System to bere-engineered

System to be

re-engineered

Re-engineered

system


35/37

35

2004 by SEC

Program Structure Improvement

Maintenance tends to corrupt the structure of a program. Itbecomes harder and harder to understand

The program may be automatically restructured to removeunconditional branches

Conditions may be simplified to make them more readable


36/37

36

2004 by SEC

Reverse Engineering

Analysing software with a view to understanding its designand specification

May be part of a re-engineering process but may also beused to re-specify a system for re-implementation

Builds a program data base and generates information fromthis

Program understanding tools (browsers, cross-referencegenerators, etc.) may be used in this process


37/37

37

The Reverse Engineering Process[SOM2004]

Data stucturediagrams

Program stucturediagrams

Traceabilitymatrices

Documentgeneration

Systeminformation

store

Automated

analysis

Manualannotation

System to bere-engineered

maintanance 2 (1)

Documents