1. Representing Systems Sixth Meeting

2. Modeling Systems Models block-diagram Used throughout engineering Represents behavior and structure of systems. Only the aspects of the system that are of interest. Structure of a system Indicates the components of a system and The relationship between them. Behavior of the system indicates what the system does. Modeling techniques Describe communication systems; A system can consist entirely of software or of hardware or both. abstraction. Ignore many of the details of the system.

3. Project B Project A Terminating the Process GM Branch Tech Mgr. Tech

4. State Transition Diagram States = symbols Transitions = directed lines. The line is labeled with the input and output signals Input signal = Causes the transition Output signals = Outcomes of the state The input and output signals are separated by a forward slash

5. Signal Sequence Diagrams Sometimes it is useful to look at a particular exchange of signals between a finite state machine and its environment. Signal sequence diagrams provide a convenient way of recording such an exchange.

6. Signal Exchange Vertical lines express the passing of time Signals are represented by sloping lines. Vertical displacement of a sloping line gives a measure of time taken.

7. Object Oriented Models An object Is a collection of data items or attributes together with operations which use that data. Corresponds to the ‘real’ objects. Encapsulation The data and operations are kept together, (i.E., Data and behavior.) Easier to maintain and modify. Re-use The systems can be built using pre-existing program elements, i.E.,.

8. Class A collection of same-type objects. A sub-class A class of objects which is a specialization of an existing class Parent class (super class) The specialization relationship of classes and subclasses.

10. Class - Details Attributes A collection of data items relating to the component of the system For example, the attributes of a ‘cursor’ object X-position Y-position Shape Operations Action which objects of that class can carry out. Referred to as services or methods. Inheritance Attributes and operations defined in the parent class For example, a scrolling window will inherit All the attributes and operations of the ‘window’ class, and It own attributes and operations

11. Different classes having operations with the same name For example, a system may need ‘scaleable windows’ whose contents shrink or grow when the window is resized. The ‘Scaleable window’ class would be a subclass of the ‘Window’ class but the resize operation for the scaleable window would have different implementation. Class – Polymorphism

12. Class - Client Server Messages sent from one object to another. For example, when a window on a computer screen is activated its title bar changes color to reflect this. The window object sends a message to the title bar object.