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Patterns in Software Engineering Lecturer: Raman Ramsin^ Lecture 13^ Reengineering Patterns

Part 1

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Part

Patterns in Software Engineering – Lecture 13 ReengineeringReengineering „ Goal of Reengineering

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^ Reducing the complexity of a

legacy system

sufficiently so that it can

continue to be used and adapted at an acceptable cost. „^

Reasons for Reengineering^

Unbundling a monolithic system

so that the individual parts can be

^ Unbundling

a monolithic system

so that the individual parts can be

more easily marketed separately or combined in different ways. Improving performance. Porting the system to a new platform. Extracting the design

as a first step to a new implementation.

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xploiting new technology

as a step toward cutting maintenance costs.

^ Reducing human dependencies

by documenting knowledge about the

system and making it easier to maintain.

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Patterns in Software Engineering – Lecture 13 Reengineering LifecycleReengineering

Lifecycle

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Patterns in Software Engineering – Lecture 13 Reengineering Problems: ArchitecturalReengineering

Problems: Architectural

„

Insufficient documentation:

Documentation either does not

„

Insufficient

documentation: Documentation either does not

exist or is inconsistent with reality. „

Improper layering: Missing or improper layering hampers „

Improper layering: Missing or improper layering hampersportability and adaptability. „

Lack of modularity: Strong coupling between modules hampers „

Lack of modularity: Strong coupling between modules hampersevolution.D^

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Duplicated code: "Copy, paste, and edit" is quick and easy, butleads to maintenance nightmares.D^

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Duplicated functionality: Similar functionality is reimplementedby separate teams, leading to code bloat.

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Patterns in Software Engineering – Lecture 13 Reengineering PatternsReengineering

Patterns

„

Reengineering patterns

codify and record knowledge about

modifying legacy software.modifying legacy software. „^

They are stable units of expertise that can be consulted in anyreengineering effort:reengineering effort:^

they help in diagnosing problems and identifying weaknesses that mayhinder further development of the system

and

hinder further development of the system, and they aid in finding solutions that are more appropriate to the newrequirementsrequirements.

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Patterns in Software Engineering – Lecture 13 Reengineering Patterns: CategoriesReengineering

Patterns: Categories

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Patterns in Software Engineering – Lecture 13 Reengineering Patterns: Categories (2)Reengineering

Patterns: Categories (2)

6

Migration Strategies:

help keep a system running while it is being

6.^

Migration Strategies:

help keep a system running while it is being

reengineered and increase the chances that the new system will beaccepted by its users.

7.^

Detecting Duplicated Code:

help identify locations where code may

have been copied and pasted, or merged from different versions ofthe software.

8.^

Redistribute Responsibilities:

help discover and reengineer classes

with too many responsibilities.

9.^

Transform Conditionals to Polymorphism:

help redistribute

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responsibilities when an object-oriented design has beencompromised over time.

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Patterns in Software Engineering – Lecture 13 Reengineering Patterns:

Setting Direction

Reengineering

Patterns:

Setting

Direction

Problem:

How do you establish a common sense of purpose in a team? Solution:

Establish the key priorities for the project and identify guidingfor the project and identify guidingprinciples that will help the team tostay on track.

Problem:

Which problems should you focus on first? Solution:

Start working on the aspects that are most valuable to yourcustomer.customer. Problem:

Which parts of a legacy system should you reengineer and

Problem:

How do you maintain architectural vision during the course of acomplex project? Solution:

Appoint a specific person whose responsibility in the role of Navigator is to

which should you leave as they are? Solution:

Only fix the parts that are "broken"- those that can no longer beadapted to planned changes.

responsibility in the role of Navigator is toensure that the architectural vision ismaintained.

Problem:

How do you keep your team synchronized? Solution:

Hold brief regular round Solution:

Hold brief, regular round table meetings.^ Problem:

How can you possibly tackle all the reported problems? Solution:

Address the source of a problem, th^ th

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Problem:

How much flexibility should you try to build into the new system? Solution:

Prefer an adequate but simple solution to a potentially more

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rather than particular requests of yourStakeholders.

simple solution to a potentially moregeneral but complex solution.

Patterns in Software Engineering – Lecture 13 Reengineering Patterns:

Initial Understanding

Reengineering

Patterns:

Initial

Understanding

Problem

: How do you recover the way design concepts are represented in the source code? Solution:

Use your development expertise to conceive a hypothetical class diagram representingh^ d^

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Problem

: Which object structures represent the valuable data?

the design. Refine that model by verifying whetherthe names in the class diagram occur in the sourcecode and by adapting the model accordingly.

Problem

: How can you quickly identify potential design problems in large software systems?

represent the valuable data? Solution:

Analyze the database schema and assess which structuresrepresent valuable data. Derive a classdiagram representing those entities.

Solution:

Measure the structural entities forming the software system (i.e., the inheritancehierarchy, the packages, the classes, and themethods) and look for exceptions in thequantitative data you collected.

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Patterns in Software Engineering – Lecture 13 Reengineering Patterns:

Detailed Model Capture

Reengineering

Patterns:

Detailed

Model Capture^ Problem

: How can you understand a cryptic piece of code? Solution:

Iteratively rename and refactor the code to introduce meaningful names and to make sure

Problem

: How do you keep track of, synchronize and share yourunderstanding about a piece of codeand the questions that you have? S^ l^ ti

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the structure of the code reflects what the system isactually doing.

Problem

: How do you discover which Solution:

While you are working on the code, annotate it directly with thequestions you are facing.^ Problem

: How do you discover which objects are instantiated at run time andhow they collaborate? Solution:

Run each of the scenarios and use your debugger to step through thecode.

Problem

: How can you discover why the system is designed the way it is? Which parts of the system are stable and whichparts aren't? Solution:

Use tools to find entities where functionality has

Problem

: How do you determine which contracts

a class supports? Solution:

Look for common programming idioms that expose the way clients makeuse of the class interface. Generalize yourb^

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been removed (sign of a consolidating design), and entitiesthat change often (sign of an unstable part of the design).

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observations in the form of

contracts.

Patterns in Software Engineering – Lecture 13 Reengineering Patterns: Migration StrategiesReengineering

Patterns: Migration Strategies

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Patterns in Software Engineering – Lecture 13 R fReference „ Demeyer, S., Ducasse, S., and Nierstrasz, O.,

Object-Oriented

Reengineering Patterns, Elsevier Science, 2003.

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