Software Engineering 2003 Jyrki Nummenmaa 1 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.

Software Engineering 2003 Jyrki Nummenmaa 2 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.

Software Engineering 2003 Jyrki Nummenmaa 3 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.

Software Engineering 2003 Jyrki Nummenmaa 4 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

Software Engineering 2003 Jyrki Nummenmaa 5 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.

Software Engineering 2003 Jyrki Nummenmaa 6 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.

Software Engineering 2003 Jyrki Nummenmaa 7 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

Software Engineering 2003 Jyrki Nummenmaa 8 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.

Software Engineering 2003 Jyrki Nummenmaa 9 Subject {abstract} Subject {abstract} Object {abstract} Object {abstract} update() {abstract} ConcreteSubject ConcereteObserver update() observes * registers for all g in observes { g.update() } attach(x:Observer) detach(x: Observer) notify() Class Diagram for Observer Design Pattern

Software Engineering 2003 Jyrki Nummenmaa 10 :ConcreteSubject t1:ConcreteObserver attach(t1) update() t2:ConcereteObserver attach(t2) notify() update() Changes State A Sequence Diagram For Observer Design Pattern

Software Engineering 2003 Jyrki Nummenmaa 11 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.

Software Engineering 2003 Jyrki Nummenmaa 12 Subject {abstract} Subject {abstract} Object {abstract} Object {abstract} update() {abstract} GameModel GameGUI update() observes * registers for all g in observes { g.update() } attach(x:Observer) detach(x: Observer) notify() Applying The Observer Design Pattern Controller?

Software Engineering 2003 Jyrki Nummenmaa 13 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.

Software Engineering 2003 Jyrki Nummenmaa 14 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

Software Engineering 2003 Jyrki Nummenmaa 15 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.

Software Engineering 2003 Jyrki Nummenmaa 16 ComponentZ ComponentY InterfaceX Component Diagram implements uses Interface – this may also be represented with stereotype > for a class. component

Software Engineering 2003 Jyrki Nummenmaa 17 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.

Software Engineering 2003 Jyrki Nummenmaa 18 Component Technologies Microsoft COM & DCOM (distributed COM) CORBA standard –several vendors –heavyweight system Java Beans

Software Engineering 2003 Jyrki Nummenmaa 19 GameGUI Game Controller GameModel GameModelInterface GameControllerInterface Component Diagram For The Game Application

Software Engineering 2003 Jyrki Nummenmaa 20 User Choose to take card Show funds Card Value Sequence Diagram for ”Take Card” at Component Level Pay (1) Updated funds Turn Card Show card value Add Funds (Value) Show funds GameView GameController GameModel Take card Show funds Show card value Updated funds Show funds

Software Engineering 2003 Jyrki Nummenmaa 21 : GameClient : GameServer : GameModel : GameController : GUI > Deployment Diagram Processing resource (a device, not a device type) Component instance Object – ok, this was a component in an earlier slide, this is just for example