Chapter 5: Software Re-Engineering Omar Meqdadi SE 3860 Lecture 5 Department of Computer Science and Software Engineering University of Wisconsin-Platteville

2 Topic Covered Software Re-engineering Life-Cycle of Software Re-engineering Reverse Engineering Software Re-engineering Process

3 Definitions Forward Engineering is the traditional process of moving from high-level abstractions and logical, implementation- independent designs to the physical implementation of a system. Reverse Engineering is the process of analyzing a subject system to Identify the system's components and their interrelationships and Create representations of the system in another form or a higher level of abstraction.

4 Definitions Reengineering - Reorganising and modifying existing software systems to make them more maintainable by first reverse engineering and then forward engineering Refactoring - A program restructuring (rearranging) in a series of small, semantics preserving transformations in order to make the code easier to maintain and modify

Forward EngineeringReverse Engineering Requirements Analysis Design Implementation Forward Engineering and Reverse Engineering

6 Forward Engineering and Re- Engineering

7 System Re-engineering A Preventive Maintenance activity Re-structuring or re-writing part or all of a legacy system without changing its functionality Applicable where some but not all sub-systems of a larger system require frequent maintenance Re-engineering involves adding effort to make them easier to maintain. The system may be re-structured and re-documented.

8 When to Re-engineer? Port to other Platform  when hardware or software support becomes obsolete Design extraction  to improve maintainability, portability, etc. Exploitation of New Technology  new language features, standards, libraries, etc.  when tools to support restructuring are readily available

9 Re-engineering Advantages Reduced risk  There is a high risk in new software development. There may be development problems, staffing problems and specification problems Reduced cost  The cost of re-engineering is often significantly less than the costs of developing new software

10 Re-engineering Cost Factors The quality of the software to be re-engineered The tool support available for re-engineering The extent of the data conversion which is required The availability of expert staff for re-engineering

11 Re-engineering Cost

Life-Cycle of Re-engineering Requirements Designs Code (1) requirement analysis (2) model capture (3) problem detection (4) problem resolution (5) program transformation people centric lightweight

Life-Cycle of Re-engineering Reverse Engineering Phase  Requirement analysis: analyze on which parts of your requirements have changed  Model capture: reverse engineer from the source-code into a more abstract form, typically some form of a design model Forwarded Engineering Phase  Problem detection: identify design problems in that abstract model  Problem resolution: propose an alternative design that will solve the identified problem  Program transformations: make the necessary changes to the code, so that it adheres to the new design yet preserves all the required functionality

14 Re-engineering Process Activities Source code translation  Convert code to a new language Reverse engineering  Analyze the program to understand it Program structure improvement  Restructure automatically for understandability Design recovery and reimplementation Pr ogram modularization  Reorganize the program structure Data reengineering  Clean-up and restructure system data

15 Source Code Translation Involves converting the code from one language (or language version) to another e.g. FORTRAN to C May be necessary because of:  Hardware platform update  Staff skill shortages  Organisational policy changes Only realistic if an automatic translator is available

16 Source Code Translation

17 Reverse Engineering Program Comprehension  Analysing existing software with a view to understand its design and specification  Systematic process of acquiring important design factors and information regarding engineering aspects from an existing product  A process which analyses a product/technology to find out the design aspects and its functions Builds a program data base and generates information from this

18 Reverse Engineering Goals Cope with complexity  need techniques to understand large, complex systems Recover lost information  extract what changes have been made and why Detect side effects  help understand ramifications of changes Synthesize higher abstractions  identify latent abstractions in software Facilitate reuse  detect candidate reusable artifacts and components

19 Reverse Engineering Activities Understanding process  source code is analyzed to at varying levels of detail  to understand procedural abstractions and overall functionality Understanding data  internal data structures  database structure Understanding user interfaces  what are basic actions processed by the interface?  what is system's behavioral response to these actions?

20 Reverse Engineering Process

21 Reverse Engineering Techniques Re-documentation  pretty printers  diagram generators  cross-reference listing generators Design recovery  software metrics  browsers  visualization tools  static analyzers  dynamic (trace) analyzers

22 Reverse Engineering for Software Maintenance Corrective maintenance:  Easier to identify defective program components and the source of residual errors Adaptive/Perfective maintenance:  Eases understanding of system’s components and their interrelationships, showing where new requirements fit and how they relate to existing components Preventive Maintenance  Represent the first phase of the re-engineering process

23 Code Restructuring (Refactoring) Maintenance tends to corrupt the structure of a program. It becomes harder and harder to understand So, the program may be automatically restructured  Source code is analyzed and violations of structured programming practices are noted and repaired  Examples: Remove unconditional branches Conditions may be simplified to make them more readable  Revised code needs to be reviewed and tested

24 Code Restructuring (Refactoring) Example1: Spaghetti logic

25 Code Restructuring (Refactoring) Example1: Structured control logic

26 Code Restructuring (Refactoring) Example2: Condition simplification -- Complex condition if not (A > B and (C F) ) ) Simplified condition if (A = D or E > F)...

27 Program Modularization The process of re-organising a program so that related program parts are collected together in a single module Usually a manual process that is carried out by program inspection and re-organisation

28 Module Types Data abstractions  Abstract data types where data structures and associated operations are grouped Hardware modules  All functions required to interface with a hardware unit Functional modules  Modules containing functions that carry out closely related tasks Process support modules  Modules where the functions support a business process or process fragment

29 Data Re-Engineering Involves analysing and reorganising the data structures (and sometimes the data values) in a program Existing data structures are reviewed for quality Integrating and centralizing multiple databases Unifying multiple, inconsistent representations Upgrading data models Objective is to create a managed data environment

30 Data Problems End-users want data on their desktop machines rather than in a file system. Systems may have to process much more data than was originally intended by their designers Redundant data may be stored in different formats in different places in the system Data naming problems  Names may be hard to understand. The same data may have different names in different programs

31 Data Problems Field length problems  The same item may be assigned different lengths in different programs Record organisation problems  Records representing the same entity may be organised differently in different programs Hard-coded literals No data dictionary

32 Data Re-engineering Approaches

33 Data Re-engineering Process

34 Data Conversion Changing the data structure organisation without changing the data values Data value conversion is very expensive. Special-purpose programs have to be written to carry out the conversion