System Desigren_OOD-9asdasdasdsasdasdasd.pdf
- 1. System design & Analysis DR. LOBNA MOHAMED ABOU EL-MAGD
- 3. Classes and Objects A class is the general template we use to define and create specific instances, or objects. Every object is associated with a class. For example, all of the objects that capture information about patients could fall into a class called Patient, because there are attributes and methods that all patients share.
- 4. Object Oriented Design Object-oriented systems focus on capturing the structure and behavior of information systems in little modules that encompass both data and processes. These little modules are known as objects
- 6. • in most object-oriented programming languages, both classes and instances of classes can have attributes and methods. •Class attributes and methods tend to be used to model attributes (or methods) that deal with issues related to all instances of the class. •For example, to create a new customer object, a message is sent to the customer class to create a new instance of itself.
- 7. Methods and Messages Methods implement an object’s behavior. A method is nothing more than an action that an object can perform. Methods are very much like a function or procedure in a traditional programming language. Messages are information sent to objects to trigger methods. A message is essentially a function or procedure call from one object to another object.
- 9. Encapsulation and Information Hiding Encapsulation is simply the combining of process and data into a single entity. The principle of information hiding suggests that only the information required to use a software module be published to the user of the module.
- 10. Inheritance Used to identify higher level, or more general, classes of objects. Common sets of attributes and methods can be organized into super classes. classes are arranged in a hierarchy whereby the super classes, or general classes, are at the top, and the subclasses, or specific classes, are at the bottom.
- 11. The relationship between the class and its superclass is known as the A-Kind-Of (AKO) relationship. For example, a salesperson is A-Kind-Of employee
- 12. Inheritance makes it simpler to define classes. Instead of repeating the attributes and methods in the employee and customer classes separately, the attributes and methods that are common to both are placed in the person class and inherited by those classes below it.
- 15. Polymorphism and Dynamic Binding Polymorphism means that the same message can be interpreted differently by different classes of objects.
- 16. Benefits of Object-Oriented Systems Analysis and Design • Concepts like polymorphism, encapsulation, and inheritance taken together allow analysts to break a complex system into smaller, more manageable components, to work on the components individually • modularity makes system development easier to grasp, easier to share among members of a project team • Finally, many people argue that “object think” is a much more realistic way to think about the real world.
- 17. UNIFIED MODELING LANGUAGE UML • The objective of the Unified Modeling Language is to provide a common vocabulary of object-based terms and diagramming techniques that is rich enough to model any systems development project from analysis to design. The current version of UML, version 2.0 • The diagrams are broken into two major groupings: • one for modeling the structure of a system • and one for modeling behavior
- 18. Structure diagrams are used for representing the data and static relationships that are in an information system. Behavior diagrams provide the analyst with a way to depict the dynamic relationships among the instances or objects that represent the business information system.
- 19. Four Fundamental UML Diagrams use case diagrams class diagrams sequence diagrams behavioral state machine diagrams.
- 20. USE CASE DIAGRAM Use cases are the primary drivers for all of the UML diagramming techniques. The use case communicates at a high level what the system needs to do.
- 21. Elements of a Use Case Diagram A use case diagram illustrates in a very simple way the main functions of the system and the different kinds of users who will interact with it.
- 24. Creating a Use Case Diagram You should note that the use case diagram is similar to information found in DFD context and level 0 diagrams. Identify Use Cases Draw the System Boundary Place the Use Cases on the Diagram Identify the Actors Add Association Relationships
- 26. CLASS DIAGRAM • The class diagram is a static model that supports the static view of the evolving system. • It shows the classes and the relationships among the classes that remain constant in the system over time. • The class diagram is very similar to the entity relationship diagram (ERD) ; however, the class diagram depicts classes, which include attributes, behaviors, and states, while entities in the ERD include only attributes.
- 27. Elements of a Class Diagram Represents a kind of person, place, or thing about which the system must capture and store information. Has a name typed in bold and centered in its top compartment. Has a list of attributes in its middle compartment. Has a list of operations in its bottom compartment. Does not explicitly show operations that are available to all classes. Represents properties that describe the state of an object.
- 28. A method Represents the actions or functions that a class can perform. Can be classified as a constructor, query, or update operation. Includes parentheses that may contain special parameters or information needed to perform the operation. An association Represents a relationship between multiple classes, or a class and itself. Is labeled by a verb phrase or a role name, whichever better represents the relationship. Can exist between one or more classes. Contains multiplicity symbols, which represent the minimum and maximum times a class instance can be associated with the related class instance.
- 30. Creating a Class Diagram Identify Classes Identify Attributes and Operations
- 31. Draw Associations between the Classes Associations
- 32. SEQUENCE DIAGRAM A sequence diagram illustrates the objects that participate in a use case and the messages that pass between them over time for one use case. A sequence diagram is a dynamic model that supports a dynamic view of the evolving systems. It shows the explicit sequence of messages that are passed between objects in a defined interaction.
- 33. Elements of a Sequence Diagram
- 36. Creating a Sequence Diagram Identify Objects For example, the instances of classes used for the Purchase A Tune scenario include Customer and Tune. These should be placed in boxes and listed across the top of the drawing.
- 37. • Add Messages passed from object to object, with the arrow pointing in the message’s transmission direction. The arrows should be placed in order from the first message to the last to show time sequence. • Place Lifeline and Execution Occurrences Last, you will need to show when objects are participating in the sequence. A vertical dotted line is added below each object to represent the object’s existence during the sequence, and an X should be placed below objects at the point on the lifeline where they are no longer interacting with other objects. You should draw a narrow rectangular box over top of the lifelines to represent when the objects are sending and receiving messages.
- 38. BEHAVIORAL STATE MACHINE DIAGRAM A behavioral state machine diagram is a dynamic model that shows the different states that a single class passes through during its life in response to events, along with its responses and actions.
- 39. Elements of a Behavioral State Machine Diagram State A state is a set of values that describes an object at a specific point in time Event An event is something that takes place at a certain point in time and changes a value(s) that describes an object, which in turn changes the object’s state.
- 41. Creating a Behavioral State Machine Diagram Identify the States The first step is to identify the various states that a selected tune will have over its lifetime. Identify the Transitions The next step is to identify the sequence of states that selected tune object will pass through during its lifetime and then determine exact what causes each state to occur.
- 43. exercise Draw the Use Case and class diagram of your project