Software re engineering

1. Software Re-engineering
Strategy for Software Change
Indu Sharma
HOD(CSE)
CPTC, Rajsamand

2. Introduction
 We have already discussed three
types of maintenance:
 Corrective Maintenance
 Adaptive Maintenance
 Perfective Maintenance
 There is one more type of
maintenance that is called:
 Preventive Maintenance

3. Introduction
 Prevention (Preventive maintenance or
reengineering): Computer software
deteriorates due to change, and because of
this, preventive maintenance, often called
software reengineering, must be conducted to
enable the software to serve the needs of its
end users. In this maintenance no new
functionality is added to the system. Rather,
the system is modified so that it can be more
easily corrected, adapted, and enhanced.

4. Legacy Systems
 Legacy systems are old systems which
are essential for business process
support. Companies rely on these
systems so they must keep them in
operation. Software evolution strategies
include maintenance, replacement,
architectural evolution and software re-
engineering.

5. Legacy Systems
 The majority of legacy systems have been
written in COBOL, a programming language
best suited to business data processing or
FORTRAN, a programming language for
scientific or mathematical programming.
These languages have limited program
structuring facilities and in the case of
FORTRAN, very limited support for data
structuring.

6. Legacy Systems
 Maintenance of these old systems is
increasingly expensive so re-engineering
these system extends their useful life time.
Re-engineering a system is cost effective
when it has a high business value but is
maintain to expensive. Re-engineering
improves the system structure, creates new
system documentation and makes it easier to
understand.

7. Software Re-Engineering
 Software re-engineering is concerned with re-
implementing legacy system to make them
more maintainable. Re-engineering may
involve re-documenting the system,
organizing and restructuring the system,
translating the system to more modern
programming language and modifying and
updating the structure and values of the
system’s data.

8. Key Advantages or Re-
engineering
 Reduced risk: there is a high risk in
redeveloping software that is essential
for an organization. Errors may be
made in the system specification, there
may be development problems etc.
 Reduced cost: the cost of re-
engineering is significantly less than the
costs of developing new software.

9. System
Specification
Design &
Implementation
New
System
Forward Engineering
Existing s/w
system
Understanding &
transformation
Re-engineered
System
Software Re-engineering
Re-engineering V/S New
Software Development

10. Re-engineering V/S New
Software Development
 The critical difference between re-
engineering and new software
development (also called forward
engineering) is the starting point for the
development. Rather than start with a
written specification, the old system
acts as a specification for the new
system.

11. The Re-engineering Process
Reverse
engineering
Program
documentation
Data
reengineering
Original data
Program
structure
improvement
Program
modularisation
Structured
program
Reengineered
data
Modularised
program
Original
program
Sourcecode
translation

12. Re-engineering Process
The input to the process is a legacy
program and the output is the modularized
version of the same program. As the same
time as program re-engineering, the data
for the system may also be re-engineered.
The activities in this re-engineering process
are: Source Code Translation,
Reverse Engineering, Program
Structure Improvement, Program
Modularization, Data Re-engineering

13. I Source Code Translation
Automatically
translatecode
Designtranslator
instructions
Identifysource
codedifferences
Manually
translatecode
Systemtobe
re-engineered
Systemtobe
re-engineered
Re-engineered
system

14. Source Code Translation
 The simplest form of s/w re-engineering is program
translation where source code in one programming
language is translated to source code in some other
language.
 Source code translation is only economically realistic
if an automated translator is available.
 In this process source in one programming language
is automatically translated in source code in some
other language. The target language may be an
updated version of the original language(eg. COBOL-
74 to COBOL-85) or may be a translated to a
completely different language(eg. FORTRAN to C)

15. Why source code translation?
 It may be necessary for the following
reasons.
i. Hardware Platform Update: The
organization may whish to change its
standard h/w platform. Compilers for the
original language may not be available
on the new h/w.

16. Why source code translation?
ii. Staff skill shortages: There may be a lack of
trained maintenance staff for the original
language. This is a particular problem where
programs were written in a non-standard
language that has now gone out of general use.
iii. Organizational Policy Changes: An
organization may decide to standardize on a
particular language to minimize it support
software costs. Maintaining many copies of old
compilers can be very expensive.

17. Why source code translation?
IV. Lack of software support: The
suppliers of the language may have
gone out of business or may discontinue
for their product.

18. II Reverse Engineering
Process
Datastucture
diagrams
Programstucture
diagrams
Traceability
matrices
Document
generation
System
information
store
Automated
analysis
Manual
annotation
Systemtobe
re-engineered

19. Reverse Engineering
 The objective of the reverse
engineering is to derive the design and
specification of a system from its source
code. It is the process of analyzing a
program in an effort to create a
representation of the program at a
higher level of abstraction than source
code.

20. III Program Structure
Improvement
 Program restructuring modifies source code and/or
data in an effort to make it easier for future changes.
 Easy to read and understand
 Unstructured control, complex conditions can also be
simplified as part of the restructuring process.
 Complex condition: if not( A>B AND (C>D OR NOT
(E>F)))…
 Simplified condition: if A<= B AND (C>=D OR E>F)…
 Use of structured control statements

21. Program Structure Improvement
 It focuses on design details of
individual modules and on local data
structures defined within modules.
The benefits of program restructuring
are:
i. Programs have higher quality-better
documentation, less complexity, and
conformance to modern s/w engineering
practices and standards.

22. Program Structure Improvement
ii. Frustration among s/w engineers who
must work on the program is reduced,
thereby improving productivity and
making learning easier.
iii. Efforts required to maintenance activities
is reduced.
iv. S/W is easier to test and debug.

23. IV Program Modularization
 Program modularization is the process of
reorganizing a program so that related parts
are collected together and considered as a
single module. Once this has been done, it
becomes easier to remove redundancy in
these related components, to optimize their
interactions and to simplify their interface with
the rest of the program.
 In some cases, this stage may involve
architectural transformation.

24. Program Modularization
 Several different types of module may be
created during the program modularization
process:
i. Data Abstractions: These are abstract data
types that are created by associating data with
processing components.
ii. Hardware modules: These modules combines
together all of the functions which are used to
control a particular h/w device.

25. Program Modularization
iii. Functional modules: These are modules which
collect together functions that carry out similar
or closely related tasks. For eg. All of the
functions concerned with input and input
validation may be incorporated in a single
module.
iv. Process support modules: These are modules
where all of the functions and the specific data
items required to support a particular business
process are grouped. For eg., in a library
system, a process support module may include
all of the functionality required to support issue
and return of books.

26. V Data Re-engineering
Process
Entityname
modification
Literal
replacement
Datadefinition
re-ordering
Data
re-formatting
Defaultvalue
conversion
Validationrule
modification
Data
analysis
Data
conversion
Data
analysis
Modified
data
Programtobere-engineered
Changesummarytables
Stage1 Stage2 Stage3

27. Data Re-engineering
 During the re-engineering process, the
storage, organization and format of data
processed by legacy programs may
have to evolve to reflect changes to the
software. The process of analyzing and
reorganizing data structures and,
sometimes, the data values in a system
to make it more understandable is
called data-reengineering.

28. Data Re-engineering
 Various reasons for modifying the data are:
i. Data Degradation: Over time, the quality of data
tends to decline. Changes to the data introduces
errors, duplicate values may have been created
and changes to the external environment may
not be reflected in the data.
eg. Change in account no. format,
e-mail address

29. Data Re-engineering
ii. Inherent limits that are built into the
program: When originally designed,
developers of many programs included
built-in-constraints on the amount of data
which would be processed. However,
programs are now often required to
process much more data that was
originally specified by their developers.
Data re-engineering may be required to
remove the limitations

30. Data Re-engineering
iii. Architectural evolution: If a centralized
system is migrated to a distributed
architecture it is essential that the
architecture should be a data
management system that can be
accessed from remote clients. This may
require a large data re-engineering effort
to move data from separate files into the
server database management system.

31. Cost of Re-engineering
 The cost of re-engineering depend on the
extent of the work that is carried out. Cost
increases from left to right so that source
code translation is the cheapest option and
re-engineering as part of the architectural
migration is the most expensive.
 Apart from the extent of the re-engineering,
the principal factors that affect re-engineering
costs are:

32. Cost of Re-engineering
i. The quality of the software to re-
engineered: The lower of the quality of
the software and its associated
documentation(if any), the higher re-
engineering costs.
ii. The tool support available for re-
engineering: The use of CASE tools to
automate most of the program changes
is normally cost effective to re-engineer a
software.

33. Cost of Re-engineering
iii. The extent of data conversion required:
If re-engineering requires large volumes of data
to be converted, this significantly increases the
process cost.
iv. The availability of expert staff: If the staff
responsible for maintaining the system can’t be
involved in the re-engineering process, this will
increase the costs. System re-engineers will
have to spend a great deal of time
understanding the system.

34. Disadvantages of S/W Re-
engineering
i. Practical limits to the extent that a system can be
improved by re-engineering. For eg. It is not
possible to convert a system written using a
functional approach to an object-oriented system.
ii. Major architectural changes can’t be carried out
automatically, so involve high additional costs.
iii. Although re-engineered system can improve
maintainability, the re-engineered system will
probably not be as maintainable as new system
developed using modern software engineering
methods.