PV260 QUALITY IN SOFTWARE
ENGINEERING
Lean Architecture and Best Practices
Ondřej Krajíček

ondrej.krajicek@ysoft.com
http://linked.in/in/ondrejkrajicek
@hedragon @ysoftdevs
Organisations which design systems are constrained to produce
designs which are copies of the communication structures of
these organisations.
—M. CONWAY
Architecture
Design
Code
ARCHITECTURE AND DESIGN
SOFTWARE ARCHITECTURE
GIVES ANSWERSTOTHE MOST
EXPENSIVE QUESTIONS.
SOFTWARE ARCHITECTURE
ISTHE SERVANT OF HIGH-PRIORITY STAKEHOLDERVALUES.
IS AS SIMPLE AS POSSIBLE, BUT NOT SIMPLER AND
IS DESIGNEDTO BE REPLACEABLE.
(TOM GILB)
• Software Architecture
• Servant to StakeholderValues
• Simple, but not Simpler
• Replaceable
SOFTWARE DESIGN IS A DECOMPOSITION
OF A SYSTEM
INTO A SET OF CONTRACTS
BASED ON
ASSOCIATED QUALITIES,
SOTHAT CONTRACTS RESPECT SYSTEM
BOUNDARIES.
SOFTWARE DESIGN IS ABOUT ANSWERSTO
QUESTIONS WHERE CHANGES GO
BEYOND A SINGLE UNIT, SUCH AS A CLASS OR A
MODULE.
CODE…
…PROVIDES
(SOMETIMES INTENDED)
BEHAVIOR.
QUALITY OFTHE DESIGN
• Extreme Programming
• SOLID GRASP Principles
• Design Patterns
• MVC / ECB Patterns
• Refactoring
EXTREME PROGRAMMING
• KISS (Keep it Simple and Stupid)
• YAGNI (You Ain’t Gonna Need it)
XP SIMPLICITY RULES
• Kent Beck’s Four Rules of Simple Design
• Tests Pass
• Expresses Intent
• No Duplication
• Minimalistic Code
TESTS PASS
• Tests tell you when you are done.
• Verification andValidationTests
• Automatic or Manual
• UnitTesting
UNITTESTING
• What is a Unit?
• Basic Structure of a UnitTest (Arrange - Act - Assert)
• Best practices?
• Single assert per test.
• Test Driven Development (Chicago vs. London School of UnitTesting)
• Black-box vs.White-box Approach
EXPRESSES INTENT
• Code comments…
• …are not enough!
• Self-documenting Code

http://c2.com/cgi/wiki?SelfDocumentingCode
EXPRESSES INTENT (2)
• Methods vs. Code Fragments

http://c2.com/cgi/wiki?MethodsVsCodeFragments
• Separate Interfaces from Implementation

http://c2.com/cgi/wiki?SeparateInterfacesFromImplementation
• Handle Errors in Context

http://c2.com/cgi/wiki?HandleErrorsInContext
HANDLING ERRORS
• Handle errors in the same place where you detected them.
• Handle errors as late as you possibly can.
NO DUPLICATION
• What can be duplicated?
• Code Blocks
• Methods
• Classes
• Functions
• Components
• Exceptions
• ?
MINIMALISTIC CODE
• What minimalism mean? What do we want to minimize?
• What can be minimized?
COUPLING AND COHESION
• Cohesion…
• How different parts of an interface / contract are related to each other and cooperate together.
• Classes with high cohesion have a split personality.
• Coupling…
• The interaction dependency between different parts of the system.
• Coupling is directly related to decomposition and you need to keep it in mind when you
decompose.
SOLID GRASP
• Single Responsibility Principle
• Open / Closed Principle
• Liskov Substitution Principle
• Interface Segregation Principle
• Dependency Inversion
GRASP
• General Responsibility Assignment Software Patterns
• A set of design patterns or aspects emphasising good coding
practices.
• Might be useful, but only after you have good understanding of
SOLID principles.
DESIGN PATTERNS
• GRASP (to some extent)
• GoF (Creational, Behavioral and Structural)
• Model-View-Controller
• Entity-Boundary-Control
FOOD FORTHOUGHT
• Example of just-in-time-design : Refactor to Open/Closed

http://blog.goyello.com/2014/02/11/example-of-just-in-time-design-refactor-to-open-closed/
• Extreme Programming Simplicity Rules

http://www.c2.com/cgi/wiki?XpSimplicityRules
• Distributed Big Balls of Mud

http://www.codingthearchitecture.com/2014/07/06/distributed_big_balls_of_mud.html
• Microservices until Macrocomplexity

https://michaelfeathers.silvrback.com/microservices-until-macro-complexity
• Microservices and the failure of Encapsulation

https://michaelfeathers.silvrback.com/microservices-and-the-failure-of-encapsulaton
• CodeSmell

http://c2.com/cgi/wiki?CodeSmell
• ClassicTDD or London School

http://codemanship.co.uk/parlezuml/blog/?postid=987
• Model-View-Controller - a terrific MVC diagram

http://alvinalexander.com/uml/uml-model-view-controller-mvc-diagram