Software Reengineering SEII-Lecture 27

1. Software ReengineeringSEII-Lecture 27 Dr. Muzafar Khan Assistant Professor Department of Computer Science CIIT, Islamabad.

2. Recap • Unified theory of software evolution • Reengineering • Business process reengineering and software reengineering • BPR model • Business definition, process identification, Process evaluation, process specification and design, prototyping, refinement and instantiation • Software reengineering process model • Inventory analysis, document restructuring, reverse engineering, code restructuring, data restructuring, forward engineering • Reverse engineering

3. Restructuring • Modification of source code and/or data • In general, no modification of all program architecture • Focus on design details of individual modules and local data structure • If it involves program architecture, it becomes forward engineering • Restructuring occurs when the basic architecture is solid

4. Code Restructuring • Better design to perform the same function • Different techniques • Warnier’s logical simplification techniques • Boolean algebra • Conversion of “spaghetti-bowl” code into structured program • Reengineering tools • Resource exchange diagram maps program module and resources • Program architecture is restructured to minimize coupling

5. Data Restructuring • Analysis of source code prior to data restructuring • Data definitions, file descriptions, I/O, and interface descriptions are evaluated • Objective is to extract data related information • It is also called data analysis • Data redesign • Data record standardization • Data name rationalization • Physical modifications to existing data structures

6. Forward Engineering [1/4] • Consider an example • “spaghetti bowl” code • Modules are 2000 statements long • Few meaningful comment lines • 290,000 statements • No other documentation • Modification options • Continue the ad hoc design • Try to understand inner workings of the program • Redesign, recode, and test the relevant portions • Complete redesign, recode, and test • No single “correct” choice

7. Forward Engineering [2/4] • Do not wait for maintenance request • Select a program that • Will remain in use for preselected number of years • Is currently being used successfully • Is likely to undergo major modifications • Option 2, 3, and 4 should be applied • Why we redevelop • The cost to maintain one line of source code may be 20 to 40 times the cost of initial development of that line

8. Forward Engineering [3/4] • Redesign of the software architecture (program and/or data structure), using modern design concepts, can greatly facilitate future maintenance • Because a prototype of the software already exists, development productivity should be much higher than average • The user now has experience with the software. Therefore, new requirements and the direction of change can be ascertained with greater ease • Automated tools for reengineering will facilitate some parts of the job • A complete software configuration (documents, programs, and data) will exist upon completion of preventive maintenance

9. Forward Engineering [4/4] • Consider a large organization • 500-2000 production programs • Ranked based on the importance • Reviewed for the possible candidates • Forward engineering process applies SE principles, concepts, and methods • It does not simply re-create a modern equivalent program of an older version • If focuses on the use of new user and technology requirements

10. Forward Engineering for Client-Server Architectures [1/2] • Many mainframe applications are reengineered to accommodate client-server architectures • Application functionality migrates to each client computer • New GUI interfaces are implemented at the client sites • Database functions are allocated to the server • Specialized functionality (e.g. compute-intensive analysis) may remain at the server site • New communications, security, archiving, and control requirements must be established at both the client and server sites • It requires business reengineering, software reengineering, and enterprise network infrastructure

11. Forward Engineering for Client-Server Architectures [2/2] • It starts with thorough analysis of the business environment • Three layers of abstraction can be identified • Database layer • Business rules layer • Client applications layer

12. Forward Engineering for Object-Oriented Architectures • Choice of many organizations • Some applications remain “as is” but some reengineered • Appropriate data, functional, and behavioral models are created by reverse engineering • If extended functionality/behavior is required, use cases are also created • Class hierarchies, object-relationship models, object-behavior models, and subsystems are defined • Component library can be used if exists for that domain • Otherwise algorithms and data structures may be reused

13. Economics of Reengineering [1/3] • Reengineering needs resources • Resources are limited that may be used for other business purposes • Cost-benefit analysis • Nine parameters are proposed • P1 = current annual maintenance cost for an application • P2= current annual operations cost for an application • P3= current annual business value of an application • P4= predicted annual maintenance cost after reengineering • P5= predicted annual operations cost after reengineering

14. Economics of Reengineering [2/3] • P6= predicted annual business value after reengineering • P7= estimated reengineering costs • P8= estimated reengineering calendar time • P9= reengineering risk factor • L = expected life of the system • Cost associated with continuing maintenance Cmaint = [P3 – (P1 + P2)] * L

15. Economics of Reengineering [3/3] • Cost associated with reengineering Creeng = P6 + (P4+ P5) * (L – P8) – (P7 * P9) • Overall benefit of reengineering Cost benefit = Creeng– Cmaint • It should be for high-priority applications • Highest cost-benefit applications can be targeted • Others can be postponed until resources are available

16. Software Reuse [1/3] • Reuse-based software engineering is a strategy • Originally, it was started as development strategy • Factors • Lower software production and maintenance costs • Faster delivery of systems • Improved software quality • Software is a valuable asset for an organization • Reuse to increase return on investment • Availability of reuse software is also dramatically increased • Open source movement • Organizations provide reusable components • Standards help to develop reusable general services

17. Software Reuse [2/3] • Application system reuse • The whole application may be reused • Application families with a common architecture • Component reuse • Subsystems to single objects • Example: pattern matching system (text-process system) may be used in a database management system • Object and function reuse • Component for a single function / an object class • Standard libraries • Concept reuse

18. Software Reuse [3/3] • Software development processes should be adapted for reuse strategy • Requirements refinement stage • Design and implementation stages may include explicit activities • Software reuse is more effective when planned as an organization-wide reuse program • Creation of reusable assets • Adaptation of development processes • Japanese industry is quite mature in reuse

19. Benefits of Software Reuse [1/2] • Increased dependability • Tested software • More reliable • Reduced process risk • Cost of existing software is already known • Margin of error is reduced in cost estimation • Effective use of specialists • No reinvent the wheel • Domain specialist can encapsulate their knowledge

20. Benefits of Software Reuse [2/2] • Standard compliance • User interface standards • Fewer mistakes • Accelerated development • Time to market • Speed up system production

21. Summary • Restructuring • Code restructuring, data restructuring • Forward engineering • Client-server architectures, object-oriented architectures • Economics of reengineering • Cost benefit analysis • Software reuse • Benefits of reuse