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Software Engineering, CPSC-4360-01, CPSC-5360-01, Lecture 5

Software Engineering, CPSC-4360-01, CPSC-5360-01, Lecture 5. Review of Last Lecture. Analysis: Software Architecture. Use Case Realization: Use Case → Sequence Diagrams. Domain Model Refinement: Domain Model → Partial Class Diagram. Overview of This Lecture. Design:

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Software Engineering, CPSC-4360-01, CPSC-5360-01, Lecture 5

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  1. Software Engineering, CPSC-4360-01, CPSC-5360-01, Lecture 5 CPSC-4360-01, CPSC-5360-01, Lecture 5

  2. Review of Last Lecture • Analysis: • Software Architecture. • Use Case Realization: • Use Case → Sequence Diagrams. • Domain Model Refinement: • Domain Model→ Partial Class Diagram. CPSC-4360-01, CPSC-5360-01, Lecture 5

  3. Overview of This Lecture • Design: • Major activities during design phase. • Tools: • Class Diagram. • Object Diagram. CPSC-4360-01, CPSC-5360-01, Lecture 5

  4. Requirement Analysis Design Implement Test Where are we now? • Flesh out the system design: • Choose the appropriate hardware and software environment. • Detail Class Design. CPSC-4360-01, CPSC-5360-01, Lecture 5

  5. Design: Overview • Inputs: • Software Architecture. • Analysis Class Diagram. • Activities: • Decide and design appropriate classes for other layers in the Software Architecture. • Refine Analysis Class Diagram: • Produce detailed Class Diagram ready for implementation. • Collaboration Diagrams to study interaction between classes. • State Chart to study behavior of a class. • Apply Design Pattern. CPSC-4360-01, CPSC-5360-01, Lecture 5

  6. Design and the Layered Architecture • Analysis shows how business functions can be implemented in the application layer. • Design extends this level of modelling to the other layers, i.e., the Presentation and Storage layers: • Studies interaction using the sequence diagrams. • Infers information about the classes. CPSC-4360-01, CPSC-5360-01, Lecture 5

  7. Design: Presentation Layer • Decide the suitable User Interface and design the classes to support. • Details about designing a good user interface is not the aim of this course. • Important points independent of the chosen User Interface: • Separation between the User Interface and Application. • Relationship between the User Interface and Application. CPSC-4360-01, CPSC-5360-01, Lecture 5

  8. Presentation Layer Revisited • System messages have been shown arriving at the controller in the Application layer: • Questions like “How the user initiates certain events?”, “How do we get this value from the users?” were ignored. • In fact, these messages have been ‘pre-processed’ in the Presentation layer: • The boundary object in the Presentation layer models the system's user interface. • User requests are received and processed before they are redirected to the controller object. • Responsible for interacting with input devices. CPSC-4360-01, CPSC-5360-01, Lecture 5

  9. Case Study 1: Graphical User Interface • Assumption: a window-based application, i.e., a Graphical User Interface will be used. • Possible sequence of initiating the Display Booking use case: • Select an appropriate menu option. • Dialogue box appear. • User enters the date and click the OK button. • Should concentrate on the steps that trigger operations in the Application layer, e.g., the last step above. CPSC-4360-01, CPSC-5360-01, Lecture 5

  10. Case Study 1: Presentation Layer • Packages are included to show the interaction between the layers. • Upon clicking the OK button: • A message submit( ) is generated which is caught by StaffUI in the Presentation Layer. • StaffUI sends a display( ) message to the BookingSystem in the Application Layer. CPSC-4360-01, CPSC-5360-01, Lecture 5

  11. Case Study 1: Mouse Event • Mouse events are handled similarly: • An user interface object translates mouse events into system messages; • Time and Table are derived from mouse coordinates. CPSC-4360-01, CPSC-5360-01, Lecture 5

  12. Case Study 1: Inferring Class Information • For GUI, there exists a series of user generated events for one use case, e.g., Transferring an existing booking by “Drag and Drop” to a new slot. Select a Booking on screen Move the mouse around “Drop” the booking to a new slot CPSC-4360-01, CPSC-5360-01, Lecture 5

  13. Case Study 1: Inferring Class Information • User generated events might not have an one-to-one correspondence with System Message. • The boundary objects may need to keep extra information to: • Remember the state of current interaction. • Deduce when to send a system message. • In the Table Transfer example, the GUI has to: • Remember that Table Transfer is being performed, even when the user moves the mouse around. • Responsible for sending the transfer() message when the mouse button is released. CPSC-4360-01, CPSC-5360-01, Lecture 5

  14. **************************************** Welcome to BR-Booking Reservation System **************************************** Display Booking Record Booking ... ... ... Your Choice -> 1 Please Input Date -> 01/01/2006 Bookings on 01/01/2006 (Sunday): Table 1: 7pm – 9pm: YJ (1234): 4 Persons 9pm – 11pm: WH (5678): 6 Persons ... ... ... ... Although the interface is very different, activities are similar: Design UI. Study Interaction. Design the UI classes. Text Based UIs are slightly easier to design as the order of events is well defined. Case Study 1: Text Based User Interface Restaurant Booking System – Text Based UI CPSC-4360-01, CPSC-5360-01, Lecture 5

  15. :Staff Case Study 1: Text Based User Interface <<Boundary>> :StaffTextUI <<Control>> :BookingSystem :Restaurant displayOpt ( ) readDate ( ) This part is the same as the Sequence Diagram in Lecture 4, Slide 37 display( date ) date getBookings ( date) … … bookings New interactions for the Presentation layer CPSC-4360-01, CPSC-5360-01, Lecture 5

  16. Presentation Layer: Summary • Activities during design phase for Presentation layer: • Decide the appropriate type of User Interface. • Draft the User Interface. • Study the interaction to perform each of the use cases: • Modifying existing sequence diagrams derived during analysis. • Derive the classes needed: • Messages. • Class attributes. • Association with classes in the Application layer. CPSC-4360-01, CPSC-5360-01, Lecture 5

  17. Storage Layer: Revisited • Most systems need persistent data which is: • Not lost when the system closes down. • Stored in the file system or a database. • A few possible choices to provide persistency: • Relational databases (RDBMS). • Object serialization (Java). • Files input/output. • Designer needs to: • Identify what data needs to be persistent. • Identify ways to save/load the data according to the storage choice. CPSC-4360-01, CPSC-5360-01, Lecture 5

  18. Designating Persistent Classes • Case Study 1: • All booking information must be saved. • But not current date, or selected bookings. CPSC-4360-01, CPSC-5360-01, Lecture 5

  19. Designating Persistent Classes • In UML, classes are the unit of persistence. • A persistent class is denoted by a tagged value {persistent}. CPSC-4360-01, CPSC-5360-01, Lecture 5

  20. Saving and Reloading Object • As an object exists only during the program execution, there is no clear counterpart in the static storage, i.e., you cannot save an “object” directly to a file. • Instead, attributes of an object are saved. • Upon reloading, the attributes are read and an object is recreated using the same attributes, giving the illusion that “object” is loaded from a static storage. • This works well for objects that contain only simple values, but what about reference? CPSC-4360-01, CPSC-5360-01, Lecture 5

  21. Preserving Association • An association between objects operates using reference (memory address): • The memory address of an object may be different upon reloading as the object is reallocated. • An identification information to locate an object is needed to restore the association. • A simple way is to assign an unique id to each object. CPSC-4360-01, CPSC-5360-01, Lecture 5

  22. Simple Example • Example to highlight the problem of saving/loading objects. • Given the code fragment below: class A { int AInt; B refB; ... } class B { int BInt; ... } • Assume we instantiated two objects of class A and link them to two objects of class B. • A memory view during execution is on next page. CPSC-4360-01, CPSC-5360-01, Lecture 5

  23. The reference of class B object is kept as a memory address (e.g., 0x00001234) in the object of class A. Simple example (memory view) …… AInt: 11111 Class A Object refB: 0x00001240 …… Class A Object AInt: 22222 refB: 0x00001234 …… Class B Object BInt: 999 …… Class B Object BInt: 888 …… CPSC-4360-01, CPSC-5360-01, Lecture 5

  24. Simple Example (after saving to file) • Suppose we save all object attributes directly to a text file: • Upon reloading, the attributes for each object are read (e.g., the first two lines for class A object). • And a new object of the desired class is instantiated with the information read. • As we have no way to influence where to place an object, the object reference no longer works…. 111110x00001240222220x00001234999888 Text file after saving 4 objects. CPSC-4360-01, CPSC-5360-01, Lecture 5

  25. Simple Example (after reloading) …… • Let us add an oid to each object. • Instead of remembering the reference, the oid is kept instead. • Note: Only one pair of objects A and B is shown on next page to simplify the diagram. Class A Object AInt: 11111 refB: 0x00001240 Class B Object BInt: 888 …… Class B Object BInt: 999 …… AInt: 22222 Class A Object refB: 0x00001234 …… …… CPSC-4360-01, CPSC-5360-01, Lecture 5

  26. Simple Example (with oid ) • The object of class A contains its own oid, as well as the oid for the class B object that it reference (B_oid). • Memory reference is used during runtime to allow quick access. …… AInt: 11111 Class A Object refB: 0x00001240 OID: 1 B_OID: 4 …… …… …… …… BInt: 888 Class B Object OID: 4 CPSC-4360-01, CPSC-5360-01, Lecture 5

  27. Simple Example (Save and Reload with oid) • The identification information oid is saved along with other attributes. • Upon reloading, the objects will be re-instantiated with the attributes saved. • The reference is restored by looking up the object that matches oid. 11111148884 Text file after saving 2 objects CPSC-4360-01, CPSC-5360-01, Lecture 5

  28. Simple Example (Restoring Reference) …… …… AInt: 11111 AInt: 11111 Class A Object Class A Object refB: ?????? refB: 0x001200 OID: 1 OID: 1 B_OID: 4 B_OID: 4 …… …… BInt: 888 BInt: 888 Class B Object Class B Object OID: 4 OID: 4 …… …… …… …… After Restoration Before Restoration CPSC-4360-01, CPSC-5360-01, Lecture 5

  29. Observations • A mapping class is needed: • To map oid to actual memory reference. • To assign oid to objects during new object creation. • Oid behaves just like a key in a database record: • The whole process is equally applicable when using DBMS instead of an I/O file. • Using an oid to identify other objects is equivalent to using a foreign key to identify other record. • DBMS is beyond the scope of this course. • However, the process/steps are still valuable insights. CPSC-4360-01, CPSC-5360-01, Lecture 5

  30. Case Study 1: Adding Persistency Support • Take the Table class as example: • A subclass is added to incorporate the oid. • A mapper class is added. CPSC-4360-01, CPSC-5360-01, Lecture 5

  31. Case Study 1: Adding Persistency Support • The PersistentTable subclass is added so that other classes that depend on the Table class will not be affected. • Incorporating oid directly into the Table class would limit the possible choice of persistency support. • The TableMapper class is responsible for creating objects of the PersistentTable class and restoring them from persistent storage if required. • Apply the same idea to other classes that require persistency support: • Booking • Customer • Etc… CPSC-4360-01, CPSC-5360-01, Lecture 5

  32. Case Study 1: Persistency Architecture • Persistent subclasses and mapper classes depend on the class they are supporting. • So, they must be in the Application layer. • The Restaurant class is dependent on mapper classes: • Restaurant uses the mapper class to create an object with persistency support. • In order to preserve layered architecture: • Split the Application layer into two sub-packages: • Domain sub-package for all classes directly related to problem domain. • Persistency sub-package for persistency support classes has minimal effect on the ‘Domain’ sub-package. • Changing the Persistency sub-package should have a minimum impact on the Domain sub-package. CPSC-4360-01, CPSC-5360-01, Lecture 5

  33. Persistency Architecture CPSC-4360-01, CPSC-5360-01, Lecture 5

  34. Persistency Sub-Package: Possible Questions • One possible way of achieving persistency has been described. • There are other possible questions: • When to save/load objects? • Load on execution starts, Save on exit? • Save on creation/modification? • Load only when needed? • Should the system provide backup? • Should the system be crash-proof? • These constraints should be taken into account when designing the persistency support. CPSC-4360-01, CPSC-5360-01, Lecture 5

  35. Storage Layer: Summary • Activities during design phase for Storage layer: • Identify classes that require persistency support. • Choose appropriate persistency service. • Introduce classes to work with the chosen persistency service. • Additional sequence diagram can be drawn to capture the operations needed. CPSC-4360-01, CPSC-5360-01, Lecture 5

  36. Design Phase: The rest of the journey • At this point, the basic technique/activity during design phase is covered. • Subsequent lectures (up to lecture 8) will take a closer look at the tools (relevant UML diagrams) and one important technique to enhance the design (design patterns). CPSC-4360-01, CPSC-5360-01, Lecture 5

  37. Detailed Class Design • Create a detailed class specification that could be used as a basis for implementation. • Start with analysis class model. • Collect messages from all realizations: • check redundancy, inconsistency, etc. • define the operation interface of class. • specify detailed parameters and return types. CPSC-4360-01, CPSC-5360-01, Lecture 5

  38. Class Name Attributes Operations Class Diagram: Review • Class is represented by: One Class • A relationship between classes is represented by an association with: • Association name. • Role name. • Multiplicity. • Nagivability (direction). CPSC-4360-01, CPSC-5360-01, Lecture 5

  39. Class Multiplicity • Multiplicity notation, e.g.: • 3 (three only, specific number). • 2..8 (two to eight only, specific range). • 1,3,5 (either one, three or five only). • * (zero to many). • Can be applied to class, known as class multiplicity: • Determine the number of instances for a class. • Default class multiplicity is *. • Special cases can be denoted as: This class can have exactly one instance during execution. Class Name 1 CPSC-4360-01, CPSC-5360-01, Lecture 5

  40. Table number: Integer places: Integer Attribute Type • Each attribute should have a type, denoted as: attribute_name: type • Example: • UML defines only Integer, String, Boolean. • Specific Programming Language types are usually allowed, e.g., Float, Double, Char, etc. • UML allows definition of a new type using enumeration. CPSC-4360-01, CPSC-5360-01, Lecture 5

  41. <<enumeration>> Color red amber green TrafficLight currentLight: Color Enumeration • Define a new datatype color with the acceptable values red, amber, green: • Usage example: The traffic light color can be either red, amber or green. The attribute currentLight can only have the values red, green or amber. CPSC-4360-01, CPSC-5360-01, Lecture 5

  42. Table number: Integer places: Integer totalTable: Integer Attribute Scope • Attribute of a class has instance scope by default: • i.e., each instance (object) of the class has an independent copy of the attribute. • There are cases where class scope is needed: • All instances share one copy of the attribute (also known as class attribute in Java). • Denote by underlining the attribute: There is only one copy of totalTableregardless of the number of Tableobjects. CPSC-4360-01, CPSC-5360-01, Lecture 5

  43. Table - number: Integer - places: Integer + totalTable: Integer Attribute Visibility • Equivalent to the accessibilitylevel in languages like C++, Java. • UML defines four levels of accessibility: • public (+): visible to all classes. • protected (#): visible to instances of subclasses. • private (-): visible only in the same class. • package (~): visible to classes in the same package. • numberand placesare private to each object. • totalTableis accessible to everyone. CPSC-4360-01, CPSC-5360-01, Lecture 5

  44. Module - examDate [0..1]: Date - staff [*]: String ... ... Attribute Multiplicity • Attribute multiplicity defines how many values an object stores for an attribute: • default is exactly 1. • optional multiplicity shows possible null values. • arrays modelled by * (many) multiplicity. CPSC-4360-01, CPSC-5360-01, Lecture 5

  45. Table - number: Integer - places: Integer + totalTable: Integer + getNumber( ): Integer + setNumber(n: Integer) + getTotal( ): Integer + Table(n: Integer, p: Integer) Operation • Operation uses the following syntax: Operation_name (parameter: type, …) : return_type • Scope and Accessibility notations are the same as the attribute’s. • Constructor is denoted as Class Scope operation in UML. CPSC-4360-01, CPSC-5360-01, Lecture 5

  46. Constructing Class Diagram • Study relevant structures (usually real world entities) and generalize to class diagram. • May be difficult in complicated cases: • We need a way to study specific examples instead of all possible scenarios. • From a few representative examples, we generalize to a structure that is able to support all cases. • An object diagram is introduced to study specific examples instead of general cases. CPSC-4360-01, CPSC-5360-01, Lecture 5

  47. Object Diagram • Classes in a program describe all possible instances (objects). • During program execution, only a subset of all possible objects are instantiated. • Similarly, UML defines Object Diagrams to examine instances (possible scenarios) of Class Diagrams: • The notation is very similar to a Class Diagram. • Slight difference in terminology. • Can help to understand and refine a Class Diagram. CPSC-4360-01, CPSC-5360-01, Lecture 5

  48. Class Diagram: Describes ALL possible Table Objects. Object Diagram: Describes ONE table object, with specific values. Operations were not included. Example Java Code to create this object: Table tableOne = new Table(1,10); Table tableOne: Table - number: Integer - places: Integer number = 1 places = 10 + getNumber( ): Integer + setNumber(n: Integer) Object Diagram: First Look CPSC-4360-01, CPSC-5360-01, Lecture 5

  49. Object Diagram: Closer Look • An object is given an object name: • Represents the identity of an object. • So that it can be easily referred in the diagram. • Usually it corresponds to the variable name in programming construct for convenient sake: • An object variable in Java is a reference. • Multiple object variable can refer to the same object. • However, one object can have only one object name in UML. • Denoted by: objectName: ClassName CPSC-4360-01, CPSC-5360-01, Lecture 5

  50. Object Diagram: Closer Look • The object name can be omitted when we are not interested in knowing the exact object in action: :Person • The attributes of an object have specific values. • Denoted by: attributeName = value • Operations of an object are not shown as all objects of the same class have the same set of operations. CPSC-4360-01, CPSC-5360-01, Lecture 5

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