OBJECT ARCHITECTURE DESIGN These slides continue with our example application, based on the simplified OMT-based technique. I am not trying to cover all or not even most aspects here. We will have other examples to show how things can be done differently. 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

What Is Architectural Design? Choices Made In Architectural Design: Components High-Level Design Patterns Architectural Styles A Possible Framework Architecture Processes and Hardware Processes and Communication Other Architecture-Related Decisions  -> Some of these issues depend on each other strongly. 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Why Architectural Design? Managing complexity It is easier to manage complexity, if we divide the application into reasonable parts. Maintainability Usually a reasonable architecture makes it much easier to maintain the software. This may actually be the biggest reason for architectural design. Efficiency A good architecture enables us to isolate the potential causes for inefficiency and makes it possible to scale up performance when load increases. 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Input Information For Architecture Design Analysis model of the application showing what the system is about and what it should do. Hardware environment Software environment - possible database management system - communication technologies - programming language – if known - target operating system(s) – if known 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Architectural Design For Example Game Application Clearly, it seems reasonable to separate the game logic from the user interface. If done suitably, this will also enable multiple client applications with a view to the same game. This kind of an approach is actually quite usual. In fact, so usual, that there is a well-known architectural solution for this kind of setting, called Model-View-Controller architecture (MVC architecture). We will study a variant of MVC from a separate set of slides by Ari Jaaksi, Nokia. 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Design Patterns Our design could follow the principles of MVC (or MVC++) directly. Another possibility is to copy an existing design idea and modify it to our needs. The idea of copying designs like this is the basic idea behind design patterns. It has been difficult to reuse code. The idea of design patterns is to reuse ideas. In a way, applying the MVC model is reusing the idea. However, there have been efforts to give a fixed format for presenting design patterns. 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Design Pattern Description Name Problem Solution Static: E.g. Class Diagram Dynamic: E.g. Sequence Diagram Strategy How to implement the pattern Consequences Results and trade-offs 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Design Pattern ”Observer” Problem: We want to keep a number of objects (observers) aware of the state of an object (subject) This is done by making the observers subscribe to the subject. Whenever the subjects state changes, it will publish information about that to all subscribed observers. 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Class Diagram for Observer Design Pattern observes Object {abstract} update() {abstract} Subject {abstract} * attach(x:Observer) detach(x: Observer) notify() for all g in observes { g.update() } registers ConcereteObserver update() ConcreteSubject 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

A Sequence Diagram For Observer Design Pattern :ConcreteSubject t1:ConcreteObserver t2:ConcereteObserver attach(t1) attach(t2) Changes State notify() update() update() 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Some observations A subject and the respective observers need minimal information on each other. In fact, they need to implement the required operations (attach, detach, notify, update), but that’s about that. This way, we get a high level of independence in their implementations. 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Applying The Observer Design Pattern observes Object {abstract} update() {abstract} Subject {abstract} * attach(x:Observer) detach(x: Observer) notify() for all g in observes { g.update() } registers GameGUI update() GameModel Controller? 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Applying The Observer Pattern Apparently, we can use the Observer pattern for the user interface to observe the state of the game. Q: How is this different from using the MVC model? A: This model does not include the control part, ie. it is more appropriate for situations, where observing is enough. This way, MVC seems more appropriate for our game example. -> Back to the drawing board. The MVC looked better. However, we will look at yet another possibility: components. 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Components - What? Component technologies can be seen as packaging technologies Independent Can be used as a building block to build larger systems – dynamic, ”plug & play” linking Have a well-defined interface, which hides the implementation completely Can be treated as a product of its own Can be installed separately Can be implemented with any language, as long as it implements the necessary interfaces 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Components - Why? Object-oriented source-level re-use of code requires same source code language. Object-oriented source-level re-use may require understanding of the implementation. Building the system from source-level pieces requires that these pieces compile happily with each other. We want to avoid the above problems and build binary components with well-defined interfaces. 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Component Diagram implements uses Interface – this may also be represented with stereotype <<interface>> for a class. ComponentZ InterfaceX ComponentY component 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Component - Interfaces An interfaces defines a set of services, which semantically belong together. An interface is a contract between the user and the implementor. A componenent may implement many interfaces and an interface may be implemented by many components. Once an interface is released, it does not change. If changes are necessary, a new interface is released. As a matter of fact, you should know all this. 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Component Technologies Microsoft COM & DCOM (distributed COM) CORBA standard several vendors heavyweight system Java Beans 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Component Diagram For The Game Application GameGUI Game Controller GameControllerInterface GameModel GameModelInterface 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Sequence Diagram for ”Take Card” at Component Level GameView GameController GameModel User Choose to take card Take card Pay (1) Show funds Show funds Updated funds Turn Card Show card value Card Value Show card value Add Funds (Value) Show funds Updated funds Show funds 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa

Deployment Diagram Processing resource (a device, not a device type) : GameClient : GameServer : GUI : GameModel <<TCP/IP>> : GameController Component instance Object – ok, this was a component in an earlier slide, this is just for example 4.10.2004 Software Engineering 2004 Jyrki Nummenmaa