2. 2
• Sorry, this is an English slide
• I am a good man
– Don’t ask where the (bad) examples come from
• The patterns and methods mentioned today
can be found in the following books
Taking the Teddy’s courses is one of the fastest ways
DP POSA RF PEAA
Warning
3. 3
Alien?
Do you believe
evolutional software
architecture?
I want to believe
4. 4
• Before the doom, I received the Ph. D. degree
About me
5. 5
• Recently, I updated my profile on Link-in
– Six-year teaching assist
(Saw many bad examples)
– A distributed wireless communication protocol
(WiMAX) simulator and emulator
(Project Manager, Aug 2006 – July 2009)
– An embedded DVB-H transport stream decoder
(Scrum Master, Aug 2009 – July 2011)
– A configurable conference management system &
A distributed load testing framework
(Consultant and test planner, Aug 2011 – July 2012)
– An Android game framework for teaching OOP Lab
(Major refactoring for release, Jan 2012 – Apr 2012)
The experiences
7. 7
• Recall the first year of the first project
– Chaos, spaghetti, etc.
• Starting of the second year
– Requirement change: 802.16d 802.16e
– Throw away vs. refactoring
– I played both the PM and SA roles.
– The architecture design took almost three months.
– However, it did work!!
– In addition, we were happy to add new functions
in the third year.
“Big design up front” won this time
8. 8
Mobile Station
Base Station
Application
Application Socket
Socket Driver
Driver
MAC Single Layer
Simulation
MAC SECU
Gateway UI & Console
SECU Agent
PHY1
Agent SYS UI
PHY1 Agent MAC PHY Agent
PHY2
PHY2 CHN CHN MIMO Routing Table Conf. SPMT
Plug-in Plug-in
Data Control Data Control Data Control Data Control
Socket Socket Socket Socket Socket Socket Socket Socket Control Socket
2 sheets of A2 paper class diagram, 15 sheets of A4
paper sequence diagrams, and totally over 180k LOC
The architecture
9. 9
• In the second project
– I was the scrum master of a sub-project, but was
compelled to be the SA of the main project
– The architecture design took almost four months
– Well, it did work, again!!
• In our sub-project, all features completed near 2-month
before the due day
Signal 1
Signal 2
具DVB-H訊號接受器與
具Bluetooth或WiFi之
DVB-H訊號源 Bluetooth或WiFi之裝置A
平板B (需使用本套件)
(需使用本套件)
“Big design up front” won, again
10. 10
• In the following projects
– When I involved, chaos or close to chaos
– “Throw away” is forbidden
– Refactoring adding new features chaos
refactoring adding new features chaos
refactoring, ...
– Evolutional software architecture also works?
• Especially, after I refactored the Android game
framework
The things that changed my mindset
11. 11
always
usually
often
• I sometimes use MVC in a GUI application
rarely
never
• Why do we use MVC? POSA
– Separation of concern
– Focus on the problem domain
– Reusable model, etc.
Starting from the MVC pattern
12. 12
• Do we implement the MVC correctly?
– Are you kidding?
– In Android, Activity is a model, view, or controller?
An Activity is an application component that provides a screen with which
users can interact in order to do something, such as dial the phone, take a
photo, send an email, or view a map. Each activity is given a window in which
to draw its user interface. The window typically fills the screen, but may be
smaller than the screen and float on top of other windows.
http://developer.android.com/guide/components/activities.html
MVC implementation is easy?
13. 13
• I don’t how to test my Android App quickly!!
– I know the advantages of unit tests, but I wrote all
the logics in the activities.
– Using the Android testing and Instrumentation
framework is very slow.
ATMTextConsole ATMSwingApp ATMAndroidApp
ATMCore ATMCore ATMCore
(100% Tested) (100% Tested) (100% Tested)
How to test an Android App?
14. 14
• Extract method and extract class RF
View
View
View
Controller
Controller
Model
View
View
Controller Presentation Controller
Model
Model
Evolution to MVC
15. 15
public class CalculatorModel {
public Number LeftOperand { get; };
public Number RightOperand { get; };
public Number Result { get; };
public void InputDigit(Button button, TextBox result) {
// Append the value of the button to the right operand
// Update the text displayed on the text box
}
}
public class CalculatorView : Form { Any problem?
public CalculatorView(CalculatorModel model) {
...
Nine.Click += new EventHandler(DigitPressed);
}
private void DigitPressed(object sender, EventArgs e) {
Model.InputDigit((Button)sender, ResultTextBox);
}
}
An example
16. 16
• Observer and Strategy pattern DP
– Hollywood Principle: don't call us, we'll call you
View
Strategy Observer Strategy & Observer
Presentation Controller
Program to abstraction Program to abstraction
Model
Direct
Indirect
Dependencies between MVC
17. 17
• In the O’Reilly head first series, you often see
– “lots of customers love your program, and your
boss wants a better program that has ...”
– The boss wants a cloud-based App
• Client server pattern is a good choice POSA
– Who is on the server and who is on the client?
Client Server
View
Model
Controller
Client-server architecture
18. 18
• How do the model in the server side notify the
observer (view) in the client slide?
– Assume a connection is always kept between a
client and the server
– Remote proxy DP
Client Server
View
Model
Controller
Model Proxy Observer Stub Observer Proxy Model Stub
Methods won’t be like methods
19. 19
• Web application – one of the most popular
connectionless client-server architecture
– Decode the URLs
– Call the correct methods
– Keep the model state Server
– Object creation
Model
Client (Browser) Session (Container)
View Command (Struts 2 Action) DP
(AJAX Controller) Front Controller (Container) PEAA
Connectionless client server
20. 20
• Two different models
– Object domain model (class diagram)
• Behavior, inheritance, and polymorphism
• Composition with collection (list, map, etc.)
• Direct (dot) navigation
– Data model (ERD for relational databases)
• Composition with foreign key mapping (and relation
tables)
• SQL join
– Data mapper PEAA
• Extract the persistence logic from the domain model
Persistence
21. 21
<<interface>>
core::PreferencesManager
<<interface>>
core::Preferences +loadPreferences(in preferences : Preferences)
1 +savePreferences(in preferences : Preferences)
+setPreference(in key : string, in value : string)
+getPreference(in key : string) : string
+getPreferenceKeys() : string[] 1
+addPreferencesListener(in listener : PreferencesListener) 1
+removePreferencesListener(in listener : PreferencesListener)
<<interface>>
1 core::ComicSurferModel
<<interface>>
core::LanguageManager +initialize()
+exit()
+initialize(in path : string)
1 +getNavigator() : NavigationModel
+loadLanguage(in name : String) : bool 1
+getDisplayModel() : ImageDisplayModel
+getLocalizedText(in key : string) : string
+getMotionController() : MotionController
+getCurrentLanguage() : string
1 +getLanguageManager() : LanguageManager
+setCurrentLanguage(in name : string) : string
+getPreferences() : Preferences
+getAvailableLanguages() : Set<string>
+getViewHistory() : ViewHistory
+addLanguageChangeListener(in listener : LanguageChangeListener)
+getReaderManager() : ComicBookSuiteReaderManager
+removeLanguageChangeListener(in listener : LanguageChangeListener)
+getParallelTaskQueue() : BlockingQueue<Runnable>
<<interface>> 1
core::ViewHistory 1 1
+getRecordCount() : int
+getMaximumRecordCapacity() : int <<interface>>
+getLastRecord() : ViewRecord core::ViewHistoryManager
+getRecord(in index : int) : ViewRecord +saveHistory(in history : ViewHistory)
+getRecord(in name : string) : ViewRecord +loadHistory(in history : ViewHistory)
+getRecords() : Iterator<ViewRecord>
+setLastViewRecord(in name : string, in uri : URI, in volume : int, in page : int)
+setMaximumRecordCapacity() : int
+addViewHistoryListener()
Data mapper example
22. 22
• Comic surfer supports many formats
– How about ISO, RAR, or comic books on the web?
Comic Surfer readers
23. 23
• Plug-in pattern can be seen is many software
and platforms PEAA
– Eclipse, Firefox, Chrome, etc.
– Extend additional functionalities
• Plug-in can be designed with many techniques
– Reflection for instantiating objects
– Factory method for plug-in initialization DP
– Strategy for utilizing plug-ins DP
– Command for invoking functions DP
– Mediator for plug-in communication DP
Plug-in architecture pattern
25. 25
• When the plug-in API is published
– Any modification could make the existing plug-ins
not compatible with the host application
• Eclipse 3.8 Eclipse 4.2
– Adapter
• Great, but whose responsibility?
Compatibility issue
26. 26
• This method is NOT silver bullet
– Change interfaces and adapt changes on the
abstract classes
<<interface>>
<<interface>>
core::ComicBookSuite
core::ComicBook <<interface>>
+getComicBookCount() : int core::Page
+open()
+getComicBook(in index : int) : ComicBook
+close() +getContent() : InputStream
+getSuitePath() : string 1 1..* 1 1..*
+getPageCount() : int +close()
+getSuitePath() : URI
+getPage(in index : int) : Page
+close()
core::AbstractComicBookSuite core::AbstractComicBook core::AbstractPage
ThirdPartyComicBookSuite ThirdPartyComicBook ThirdPartyPage
How to adapt the changes?
27. 27
• When the model becomes more complicated
– The components in the model can be organized in
different logical layers POSA
http://docs.oracle.com/javase/7/docs/
Layer architecture pattern
28. 28
• Ideally, clients access only the top layer
– For some reasons, clients access the lower layer
– Even the world is not perfect,
• Law of Demeter (Façade) DP
Layer 1 Layer 1
Layer 2 Layer 2
Layer 3 Layer 3
Layer 4 Layer 4
Ideal case Real case
Visibility in layer
29. 29
• Layer substitution
– I want to change one of the layers, but it is difficult
because the upper layer depends on it directly
• Strong dependency between layers
– Why does TCP/IP works?
• Really?
• If you write a C/C++ network program, the TCP
interfaces are in different platforms (Unix/Linux socket
API vs. WinSocket API)
Dependency in layers
30. 30
• Decouple the dependency between layers
– Extract interface RF
• Two façade, one for the upper client and another for
the lower service provider
• Factory or dependency injection (Spring framework)
Façade for the upper client Adapter to the upper layer
Layer N
Interfaces for the lower service provider
Façade for the upper client Adapter to the upper layer
Layer N + 1
Interfaces for the lower service provider
Dependency inversion principle
31. 31
• The reader layer and streaming layer
nsc::MediaReader
<<interface>>
-DEFAULT_IO_SLEEP_TIME : unsigned int nsc::InputStream
-_sleepTime : unsigned int nsc::TransportStream +close()
-_stream : TransportStream*
+open() : bool
+run() +read() : char
#synchronize()
+stop() * 1 +read(in buffer : char*, in length : int) : int
+readPacket() : TransportPacket
+pause() +isAvaliable() : bool
+isRunning() : bool +isOpened() : bool
+setSleepTime(in time : unsigned int)
nsc::NetworkTransportStream nsc::FileInputStream
-_dataSocket : Socket*
<<interface>>
network::Socket
+connect(in host : string, in port : int)
+read(in data : void*, in length : int) : int
+write(in data, in length : int) : int
+close()
network::BluetoothTCPSocket network::BluetoothUDPSocket network::EthernetSocket
Dependency inversion example
32. 32
• Layers vs. tiers
– A tier is a physical deployment unit
– Web services
– Dependency inversion principle
Presentation tier
Layer 1
Layer 2
Layer 1
Layer 2
Layer 3
Layer 4 Model Service tier
Layer 3
Layer 4
From layers to tiers
33. 33
• Which machine should keep the model state?
– May the client cookie or server session help you?
– Duplicate states?
• Database state PEAA Presentation tier
• Disposable model objects Layer 1
Layer 2
– Reduce network overhead
• Data transfer objects PEAA
– Transaction Model Service tier
• Unit of work PEAA Layer 3
Layer 4
Model state
34. 34
• Concurrency vs. transaction
– Martin Fowler’s first law of distributed object
design: don’t distribute your objects!
Presentation tier Load Balancer
Layer 1
Layer 2
Model Service tier Load Balancer
Layer 3
Layer 4
Scale up
36. 36
• Evolutional software architecture is not easy
– Does big design at the start of the project avoid
changing the software architecture?
• It depends on the characters of the projects
• Requirements always change
– The following things will help you
• Why do we start from MVC? Domain model design
• Design principles and design patterns
• Unit tests, integration tests, and regression tests
• Continuous integration
• Utilize the frameworks, not be used by them
http://zh.wikipedia.org/wiki/Think_Different
Think different
37. 37
• Evolutional software architecture (refactoring)
is an endless story and harmless, not like...
Keep on the correct direction
