Software Reengineering
CIS 376
Bruce R. Maxim
UM-Dearborn
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
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
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
Business Process Reengineering Principles - part 1
• Organize around outcomes, not tasks.• Have the people who use the output of a process,
perform the process.• Incorporate information processing work into the
work that produces the raw information.• Treat geographically dispersed resources as
though they were centralized.
Business Process Reengineering Principles - part 2
• Link parallel activities instead of integrating their results.
• Put the decision point where the work is performed and build control into the process.
• Capture the data once, at its source.
Business Process Reengineering Model - part 1
• Business redefinition– business goals identified in the context of key drivers
• cost reduction
• time reduction
• quality improvement
• empowerment
• Process identification– processes critical to achieving business goals are
identified and prioritized
Business Process Reengineering Model - part 2
• Process evaluation– 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
Business Process Reengineering Model - part 3
• 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
Reengineering Processfrom Sommerville
Reverseengineering
Programdocumentation
Datareengineering
Original data
Programstructure
improvement
Programmodularisation
Structuredprogram
Reengineereddata
Modularisedprogram
Originalprogram
Source codetranslation
Software Reengineering Process Model - part 1
• 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"
Software Reengineering Process Model - part 2
• 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 and violations of structured
programming practices are noted and repaired
– revised code needs to be reviewed and tested
Software Reengineering Process Model - part 3
• 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
Forward Engineering and Reengineeringfrom Sommerville
Understanding andtransformation
Existingsoftware system
Re-engineeredsystem
Design andimplementation
Systemspecification
Newsystem
Software re-engineering
Forward engineering
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.)
Reverse Engineering Conceptspart 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
Reverse Engineering Conceptspart 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
Reverse Engineering Processfrom Sommerville
Data stucturediagrams
Program stucturediagrams
Traceabilitymatrices
Documentgeneration
Systeminformation
store
Automatedanalysis
Manualannotation
System to bere-engineered
Reverse Engineering Activitiespart 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
Reverse Engineering Activitiespart 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?
Reverse Engineering Applicability
• Reverse engineering often precedes reengineering• Sometimes reverse engineering is preferred
– if the specification and design of a system needs to be defined prior using them as input to the requirements specification process for a replacement systems
– if the design and specification for a system is needed to support program maintenance activities
Data Abstraction Recovery
• Many legacy systems make use of shared tables and global data structures to save space
• Results in tightly coupled systems that are very hard to change
• Shared data structures need to be transformed to objects or ADT’s
Creating ADT’s and Objects
• Analyze the data common areas to identify logical abstractions
• Create ADT’s or Objects for each abstraction• Provide functions or methods to update each field
in the data abstraction• Use a program browser to find all references to
these data structures and replace them with the new function or method calls
Sommerville’sRestructuring Approaches
Automated restructuringwith manual changes
Automated sourcecode conversion
Restructuring plusarchitectural changes
Automated programrestructuring
Program and datarestructuring
Increased cost
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
Types of Restructuring - part 1
• 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
Types of Restructuring - part 2
• Data restructuring– analysis of source code
– data redesign
– data record standardization
– data name rationalization
– file or database translation
Automatic Program Restructuring from Sommerville
Graphrepresentation
Programgenerator
Restructuredprogram
Analyser andgraph builder
Program to berestructured
Automatic Restructuring Problems
• Loss of source code comments• Loss of documentation• Heavy computational demands• Will not help with poor modularization problems
(e.g. related components widely dispersed throughout the source code)
• The understandability of data driven programs may not be improved by restructuring
Source Code Translation
• Involves converting the code from one language (or language version) to another
• May be necessary because of – hardware platform updates
– staff skill shortages
– organizational policy changes
• May only be realistic (e.g. cost and time effective) if an automatic translator is available
• Manual fine tuning of new code is always required
Program Translation Processfrom Sommerville
Automaticallytransla te code
Design translatorinstructions
Identify sourcecode differences
Manuallytransla te code
System to bere-engineered
System to bere-engineered
Re-engineeredsystem
Data Reengineering
• Involves analyzing and reorganizing data structures or data values used in a program
• Might be part of the process of migrating from a file-based system to a DBMS or changing from one DBMS to another DBMS
• The goal to create an environment where is managed not just used
Data Rengineering Approaches - part 1
• Data cleanup– data records and values are analyzed to improve
quality– duplicates removed– redundant information is deleted– consistent format applied to all records– normally does not require and program changes
Data Reengineering Approaches - part 2
• Data extension– data and programs are reengineered to remove
data processing limits (e.g. size or field widths)– data itself may need to rewritten to reflect
program changes
• Data migration– data is moved to modern DBMS– data might be stored in separate files or an older
DBMS
Data Problems
• Data naming problems– names be hard to understand
– heavy use of aliasing by programmers
• Field length problems– different field lengths used for same data item in different
programs
• Record organization problems– different field orderings used by different programs
• Hard-coded literals
• No data dictionary
Data Value Inconsistencies
• Inconsistent default values used in different programs (e.g. especially missing data codes)
• Inconsistent units used for same quantity (e.g. miles in one program kilometers in another)
• Inconsistent validation rules (e.g. different standards used to reject values as bad)
• Inconsistent representation semantics (e.g. multiple ways of using uppercase to convey meaning in text strings)
• Inconsistent handling of negative numbers (e.g. data validation and representation issues)
Data Reengineering Processfrom Sommerville
Entity namemodification
Literalreplacement
Data definitionre-ordering
Datare-formattingDefault value
conversion
Validation rulemodification
Dataanalysis
Dataconversion
Dataanalysis
Modifieddata
Program to be re-engineered
Change summary tables
Stage 1 Stage 2 Stage 3
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
Forward Engineering Object-Oriented Architectures - part 1
• existing software is reverse engineered so that appropriate data, functional, and behavioral models can be created
• use-cases are created if reengineered system extends functionality of application
• data models created during reverse engineering are used with CRC modeling as a basis to define classes
Forward Engineering Object-Oriented Architectures - part 2
• create class hierarchies, object-relationship models, object-behavior models and begin object-oriented design
• a component-based process model may be used if a robust component library already exists
• where components must be built from scratch, it may be possible to reuse algorithms and data structures from the original application
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
Economics of Reengineering
• Cost of maintenance = cost annual of operation and maintenance over application lifetime
• Cost of reengineering = predicted return on investment reduced by cost of implementing changes and engineering risk factors
• Cost benefit = Cost of reengineering - Cost of maintenance
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