1. System Reengineering
Restructuring or rewriting part or all of a system without changing its functionality
Applicable when some (but not all) subsystems of a larger system require frequent maintenance
Reengineering involves putting in the effort to make it easier to maintain
The reengineered system may also be restructured and should be redocumented

2. When do you decide to reengineer?
When system changes are confined to one subsystem, the subsystem needs to be reengineered
When hardware or software support becomes obsolete
When tools to support restructuring are readily available

3. Business Process Reengineering
Concerned with redesigning business processes to make them more responsive and more efficient
Often relies on the introduction of new computer systems to support the revised processes
May force software reengineering of legacy computer systems which designed to support existing processes

4. Business Process Reengineering Principles
Organize around outcomes, not tasks.
Incorporate information processing work into the work that produces the raw information.
Treat geographically dispersed resources as though they were centralized.
Link parallel activities instead of integrating their results.

5. BPR Model
A model for business process reengineering defines six activities.
Business Definition
Process Identification
Refinement and instantiation
Prototyping
Process Evaluation
Process specification
and design

6. BPR Model Business definition Process identification
business goals identified in the context of key drivers
cost reduction
time reduction
quality improvement
empowerment
Process identification
processes that are critical to achieving business goals are identified and prioritized

7. BPR Model Process evaluation Process specification and design
existing processes are analyzed and measured
process costs and time are noted
quality/performance problems are isolated
Process specification and design
use-cases are prepared for each process to be redesigned (these use-case scenarios deliver some outcome to a customer)
new tasks are designed for each process

8. BPR Model
Prototyping
used to test processes before integrating them into the business
Refinement and instantiation
based on feedback from the prototype, business processes are refined
refined processes then instantiated within a business system

9. Software reengineering process
Definition: Rebuilding a software to create another
with added functionality, better performance and reliability.
Inventory analysis
Document restructuring
Forward engineering
Reverse engineering
Data restructuring
Code restructuring

10. Software Reengineering Process Model
Inventory analysis
sorting active software applications by business criticality, longevity, current maintainability, and other local criteria
helps to identify reengineering candidates
Document restructuring options
live with weak documentation
update poor documents if they are used
fully rewrite the documentation for critical systems focusing on the "essential minimum"

11. Software Reengineering Process Model
Reverse engineering
process of design recovery
analyzing a program in an effort to create a representation of the program at some abstraction level higher than source code
Code restructuring
source code is analyzed
violations of structured programming practices are noted and repaired
revised code needs to be reviewed and tested

12. Software Reengineering Process Model
Data restructuring
usually requires full reverse engineering
current data architecture is dissected
data models are defined
existing data structures are reviewed for quality
Forward engineering
sometimes called reclamation or renovation
recovers design information from existing source code
uses this design information to reconstitute the existing system to improve its overall quality or performance

13. Forward Engineering and Reengineering from Sommerville

14. 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.)

15. Reverse Engineering Process

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

17. Reverse Engineering Activities
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?

18. Restructuring Benefits
Improved program and documentation quality
Makes programs easier to learn
improves productivity
reduces developer frustration
Reduces effort required to maintain software
Software is easier to test and debug

19. Types of Restructuring
Code restructuring
program logic modeled using Boolean algebra and series of transformation rules are applied to yield restructured logic
create resource exchange diagram showing
data types
procedures
variables shared between modules
restructure program architecture to minimize module coupling

20. Types of Restructuring
Data restructuring
analysis of source code
data redesign
data record standardization
data name rationalization
file or database translation

21. Forward Engineering Client/Server Architectures
application functionality migrates to each client computer
new GUI interfaces implemented at client sites
database functions allocated to servers
specialized functionality may remain at server site
new communications, security, archiving, and control requirements must be established at both client and server sites

22. Forward Engineering User Interfaces
understand the original user interface and how the data moves between the user interface and the remainder of the application
remodel the behavior implied by the existing user interface into a series of abstractions that have meaning in the context of a GUI
introduce improvements that make the mode of interaction more efficient
build and integrate the new GUI