1. Software Maintenance

2. What is Reverse Engineering ?
You have an unexpected case:
You finished one course project using Java
Your program runs OK
But, by accident, you delete the java file
How to hand in your project?
Reverse Engineering

3. Reverse Engineering
Analyzing software with a view to understanding its design and specification
May be part of the reengineering process
May be used to specify a system for prior to reimplementation
Program understanding tools may be useful (browsers, cross-reference generators, etc.)

4. What is Reverse Engineering ?
Forward Engineering
Reverse Engineering
Requirements
Design
Source Code
Behavior

5. What is Reverse Engineering ?
Abstraction System
Reverse Engineering
Abstraction
Forward Engineering
Re-Implementation
Old system
New System

6. What is Reverse Engineering?
RE encompasses any activity that is done to determine how a product works, to learn the ideas and technology that were used in developing that product.
RE can be done at many levels
RE generally belongs to Software Maintenance

7. Why do we need RE ? Recovery of lost information
providing proper system documentation
Assisting with maintenance
identification of side effects and anomalies
Migration to another hw/sw platform
Facilitating software reuse

8. Why do we need RE ? Benefits maintenance cost savings
quality improvements
competitive advantages
software reuse facilitation

9. Reverse Engineering Concepts part 1
Abstraction level
ideally want to be able to derive design information at the highest level possible
Completeness
level of detail provided at a given abstraction level
Interactivity
degree to which humans are integrated with automated reverse engineering tools

10. Reverse Engineering Concepts part 2
Directionality
one-way means the software engineer doing the maintenance activity is given all information extracted from source code
two-way means the information is fed to a reengineering tool that attempts to regenerate the old program
Extract abstractions
meaningful specification of processing performed is derived from old source code

11. Reverse Engineering Process

12. Reverse Engineering Activities part 1
Understanding process
source code is analyzed to at varying levels of detail
system
program
component
pattern
statement
to understand procedural abstractions and overall functionality

13. Reverse Engineering Activities part 2
Understanding data
internal data structures
database structure
User interfaces
what are the basic actions (e.g. key strokes or mouse operations) processed by the interface?
what is a compact description of the system's behavioral response to these actions?
what concept of equivalence of interfaces is relevant?

14. Difficulties of Reverse Engineering
Gap between problem
/solution domain
Gap between concrete
and abstract
Gap between coherency/disintegration
Gap between hierarchical/associational

15. Scope and Task of Reverse Engineering
program understanding
Problem/Application
domain
Mapping
Program/Implemen.
domain

16. Scope and Task of Reverse Engineering
Redocumentation and/or document generation
Recovery of design approach and design details at any level of abstraction
Identifying reusable components and components that need restructuring
Recovering business rules
Understanding high-level system description.

17. Maintenance Costs
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.)

18. Maintenance Costs (cont’d)
Time and money (software that costs £ 10 a line to develop costs £ 400 a line 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 in the maintained software
Upheaval caused during development efforts when staff must be “pulled” to work on a maintenance task

19. Maintenance Cost Factors
Team stability
Maintenance costs are reduced if the same staff are involved with them for some time
Contractual responsibility
The developers of a system may have no contractual responsibility for 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 become harder to understand and change

20. Estimation of Maintenance Cost
Maintenance efforts – 60% of the total life cycle cost.
It varies widely from one application domain to another.
2 to 4 times of the development cost.
Boehm – MC estimation as a part of COCOMO.
He defines it as a Annual Change Traffic (ACT).

21. Con.. ACT= KLOC(added) +KLOC(deleted) /KLOC(total).
KLOC(added) : Total kilo lined of source code added during maintenance.
KLOC(deleted): Total KLOC deleted during maintenance.
MC= ACT*Development cost.
The results are approximate