Garo Garabedyan's Divergent Thinking Blog

Lecture on Design Patterns, Refactoring, Sane Principles to make you a better developer by Dino Esposito

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Dino Esposito in May 14, 2009 have presented a lecture on Design Patterns, Refactoring and Sane Principles in Days of Microsoft’2009 in Faculty of Mathematics and Informatics, University of Sofia, Bulgaria, which I have attended.

These are my notes from the lecture:

Bad software design… deterioration in design. Bad software is hard to maintain and evolve. Complete redesign may not be an option. STOP at the first sign of deterioration.

Foundation of Software Design- Structured design (high cohesion; low coupling); and Separation of Concerns (modularity; information hiding). ClassA and ClassB are cohesive when changes to A have no repercussion on B. The problem is in the hidden dependencies, not in the public explicit (cohesion) dependencies.

Single Responsibility Principle (SRP)- give each class just one reason to change; and “Reason to change” == “responsibility”. In example: Invoice class does not have a responsibility to print itself.

Coupling: Level of dependency between 2 modules. ModuleA and ModuleB are coupled when changes to A force you to make changes on B.

Achieve stable constructed interfaces. ModuleA does not need to know internals of B.

Separation of Concerns (since 1974). Concern == feature of system. Taking care of each of the concerns: for each one concern, other concerns are irrelevant. Hiding implementation of behavior.

Object Oriented Design: 1st principle- Find pertinent object; 2nd principle- Program to an interface.

OOD is one paradigm. Nouns in requirements document are best candidates for classes, verbs- for functions (methods in classes).

Difference between inheritance and composition: inheritance enables polymorphism in parralel to composition, in general.

Advanced principles: 1) Open/Close; 2) Substitution; 3) Dependency Inversion. Open/Close- open for extension, close for modification; Substitution- subclasses should be substitutable for their base classes; Dependency Inversion- Low-level modules injected into the high-level module (not invoked by). Thus inverting the control of flow. Various patterns: dependency injection; service locator.

Dino Esposito ( is Microsoft Most Valuable Professional and is one of the world’s authorities on Web technology and software architecture. He writes articles covering topics such as AJAX, Silveright, software design and patterns. The event was sponsored by, Musala Soft, Microsoft and Faculty of Mathematics and Inforamtics, University of Sofia, Bulgaria. The lecture was Chapter 3 of his book Microsoft® .NET: Architecting Applications for the Enterprise (PRO-Developer).

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Written by garabedyan

May 14, 2009 at 23:43

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