Software Re-engineering
Software Re-engineering
 It is a process of software development which is done to improve the
maintainability of a software system.
 Technical Definition:
Software Re- engineering is the examination and alteration of a system to
reconstitute it in a new form.
 This process encompasses a combination of sub-processes such as
reverse engineering, restructuring, redocumentation, forward engineering,
and retargeting.
When to Re-engineer
 When system changes are mostly confined to part of the system then reengineer that part.
 When hardware or software support becomes obsolete When tools to
support re-structuring are available When to re-engineer.
Key advantages of Software Reengineering
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.
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.
 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.
 Maintenance of these old systems is increasingly expensive so reengineering these system extends their useful life time. Re-engineering
improves the system structure, creates new system documentation and
makes it easier to understand.
Re-engineering Vs New Software
Development
 Forward Engineering
System
specification
Design and
implementation
New system
Understanding and
transformation
Re-engineered
system
 Software Reengineering
Existing system
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.
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
Re-engineering Process
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(e.g. COBOL- 74 to COBOL-85) or may be a translated to a
completely different language(e.g. FORTRAN to C)
Source Code Translation
System to be
re-engineered
System to be
re-engineered
Identify
source code
differences
Design
translator
instructions
Automatically
translate
code
re-engineered
system
Manually
translate code
Why source code translation?
It may be necessary for the following reasons.
 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.
 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.
 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.
 Lack of software support:
The suppliers of the language may have gone out of business or may discontinue for their
product.
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.
Reverse Engineering
Program
structure
diagrams
Automated
analysis
System to be
reengineered
System
information
store
Document
generation
Data structure
diagrams
Manual
annotation
Traceability
metrices
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
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.
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.
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.
Program Modularization
 Several different types of module may be created during the program
modularization process:
Data Abstractions:
 These are abstract data types that are created by associating data with
processing components.
Hardware modules:
 These modules combines together all of the functions which are used to
control a particular h/w device.
Program Modularization
Functional modules:
 These are modules which collect together functions that carry out similar
or closely related tasks. For e.g. All of the functions concerned with input
and input validation may be incorporated in a single module.
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 e.g., in
a library system, a process support module may include all of the
functionality required to support issue and return of books.
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.
 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
Data Re-engineering
ii. Inherent limits that are built into the program:
When originally designed, developers of many programs included built-inconstraints 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
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.
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:
The quality of the software to re- engineered:
 The lower of the quality of the software and
documentation(if any), the higher re- engineering costs.
its
associated
Cost of Re-engineering
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.
The extent of data conversion required:
 If re-engineering requires large volumes of data to be converted, this
significantly increases the process cost.
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.
Disadvantages of S/W Re- engineering
 Major architectural changes can’t be carried out automatically, so involve
high additional costs.
 Although re-engineered system can improve maintainability, the reengineered system will probably not be as maintainable as new system
developed using modern software engineering methods.