1. Driss Kettani Sommerville, 6th edition Software Engineering II Software re-engineering l Reorganising and modifying existing software systems to make them more maintainable

2. Driss Kettani Sommerville, 6th edition Software Engineering II Topics covered l Source code translation l Reverse engineering l Program structure improvement l Program modularisation l Data re-engineering

3. Driss Kettani Sommerville, 6th edition Software Engineering II l Re-structuring or re-writing part or all of a legacy system without changing its functionality l Applicable where some but not all sub-systems of a larger system require frequent maintenance l Re-engineering involves adding effort to make them easier to maintain. The system may be re- structured and re-documented System re-engineering

4. Driss Kettani Sommerville, 6th edition Software Engineering II l When system changes are mostly confined to part of the system then re-engineer that part l When hardware or software support becomes obsolete l When tools to support re-structuring are available When to re-engineer

5. Driss Kettani Sommerville, 6th edition Software Engineering II Re-engineering advantages l Reduced risk There is a high risk in new software development. There may be development problems, staffing problems and specification problems l Reduced cost The cost of re-engineering is often significantly less than the costs of developing new software

6. Driss Kettani Sommerville, 6th edition Software Engineering II Forward engineering and re-engineering

7. Driss Kettani Sommerville, 6th edition Software Engineering II The re-engineering process

8. Driss Kettani Sommerville, 6th edition Software Engineering II Source code translation l Involves converting the code from one language (or language version) to another e.g. FORTRAN to C l May be necessary because of: Hardware platform update Staff skill shortages Organisational policy changes l Only realistic if an automatic translator is available

9. Driss Kettani Sommerville, 6th edition Software Engineering II Reverse engineering l Analysing software with a view to understanding its design and specification l May be part of a re-engineering process but may also be used to re-specify a system for re-implementation l Builds a program data base and generates information from this l Program understanding tools (browsers, cross- reference generators, etc.) may be used in this process

10. Driss Kettani Sommerville, 6th edition Software Engineering II The reverse engineering process

11. Driss Kettani Sommerville, 6th edition Software Engineering II Program structure improvement l Maintenance tends to corrupt the structure of a program. It becomes harder and harder to understand l The program may be automatically restructured to remove unconditional branches l Conditions may be simplified to make them more readable

12. Driss Kettani Sommerville, 6th edition Software Engineering II Spaghetti logic

13. Driss Kettani Sommerville, 6th edition Software Engineering II Structured control logic

14. Driss Kettani Sommerville, 6th edition Software Engineering II Condition simplification

15. Driss Kettani Sommerville, 6th edition Software Engineering II Automatic program restructuring

16. Driss Kettani Sommerville, 6th edition Software Engineering II Restructuring problems l Problems with re-structuring are: Loss of comments Loss of documentation Heavy computational demands l Restructuring doesn’t help with poor modularisation where related components are dispersed throughout the code l The understandability of data-driven programs may not be improved by re-structuring

17. Driss Kettani Sommerville, 6th edition Software Engineering II Program modularisation l The process of re-organising a program so that related program parts are collected together in a single module l Usually a manual process that is carried out by program inspection and re-organisation

18. Driss Kettani Sommerville, 6th edition Software Engineering II Module types l Data abstractions Abstract data types where data structures and associated operations are grouped l Hardware modules All functions required to interface with a hardware unit l Functional modules Modules containing functions that carry out closely related tasks l Etc.

19. Driss Kettani Sommerville, 6th edition Software Engineering II Data abstraction recovery l Analyse common data areas to identify logical abstractions l Create an abstract data type or object class for each of these abstractions l Provide functions to access and update each field of the data abstraction l Use a program browser to find calls to these data abstractions and replace these with the new defined functions

20. Driss Kettani Sommerville, 6th edition Software Engineering II Data re-engineering l Involves analysing and reorganising the data structures (and sometimes the data values) in a program l May be part of the process of migrating from a file-based system to a DBMS-based system or changing from one DBMS to another l Objective is to create a managed data environment

21. Driss Kettani Sommerville, 6th edition Software Engineering II Approaches to data re-engineering

22. Driss Kettani Sommerville, 6th edition Software Engineering II Data problems l Data naming problems Names may be hard to understand. The same data may have different names in different programs l Field length problems The same item may be assigned different lengths in different programs l Record organisation problems Records representing the same entity may be organised differently in different programs l Hard-coded literals l No data dictionary

23. Driss Kettani Sommerville, 6th edition Software Engineering II Data value inconsistencies

24. Driss Kettani Sommerville, 6th edition Software Engineering II Key points l The objective of re-engineering is to improve the system structure to make it easier to understand and maintain l The re-engineering process involves source code translation, reverse engineering, program structure improvement, program modularisation and data re-engineering l Source code translation is the automatic conversion of of program in one language to another

25. Driss Kettani Sommerville, 6th edition Software Engineering II Key points l Reverse engineering is the process of deriving the system design and specification from its source code l Program structure improvement replaces unstructured control constructs with while loops and simple conditionals l Program modularisation involves reorganisation to group related items l Data re-engineering may be necessary because of inconsistent data management