1 CS 501 Spring 2002 CS 501: Software Engineering Lecture 15 System Architecture III

2 CS 501 Spring 2002 Administration

3 CS 501 Spring 2002 Software Reuse: Application Packages Package supports a standard application (e.g., payroll, user interface to Internet information, mathematical algorithms) Functionality can be enhanced by: => configuration parameters (e.g., table driven) => extensibility at defined interfaces => custom written source code extensions

4 CS 501 Spring 2002 Reuse: Object Oriented Software Engineering Example: Java is a relatively straightforward language with a very rich set of class hierarchies. Java programs derive much of their functionality from standard classes Learning and understanding the classes is difficult. => Java experts can write complex systems quickly => Inexperienced Java programmers write inelegant and buggy programs

5 CS 501 Spring 2002 Reuse: Objects - Basic Definitions An object is a piece of code that owns attributes and provides services through methods. The methods operate on instance data owned by the object. A class is a collection of like objects.

6 CS 501 Spring 2002 Reuse: Objects - Characteristics Encapsulation. An object has a public interface that defines how other objects or applications can interact with it. methods public instance data Inheritance. Subclasses can be derived from parent classes. They inherit or override the parents' methods and instance data. Polymorphism. The effect of a method can vary depending on the class that implements it (e.g., display_object)

7 CS 501 Spring 2002 Reuse: Objects - Object Binding Binding is the linking of the software interface between two objects. Static binding: The interface is determined at compile or build time. Straightforward Allows type checking Dynamic binding or late binding: The link is established at run time. Flexible and extensible Complex

8 CS 501 Spring 2002 Reuse: Objects - Distributed Objects Objects on separate computers interact through method calls and instance data. Major systems: CORBA (Common Object Request Broker Architecture) Microsoft family: OLE, COM, DCOM, Active X,.net

9 CS 501 Spring 2002 Desirable Properties of Distributed Objects Different languages and operating environments Reusable code: components Architecture can be extensible Future changes can be localized Standard tools used for client/server interactions

10 CS 501 Spring 2002 Object Request Broker (ORB) Objects C C++ Java Other Cobol IDL ClientServer IDL Object Request Broker Interface

11 CS 501 Spring 2002 Example: Fedora IDL A research project to explore extensibility: -- very simple Interface Definition Language -- powerful tools for extensions -- interoperability experiments, Cornell and CNRI

12 CS 501 Spring 2002 Interface Definition Language module { ; interface [: ] { See next slide } interface [: ] {..... } { Naming context Define a class

13 CS 501 Spring 2002 Interface Definition Language (continued) interface [: ] { ; [ ( ) [raises exception] [context];.... [ ( ) [raises exception] [context];.... } Define a class Define a method

14 CS 501 Spring 2002 ORB: Programmer's View Object Request Broker Invoke a on object X Invoke a on object Y Object X a Object Y a ClientServer

15 CS 501 Spring 2002 Object Request Broker (ORB) An ORB lets objects make requests to and receive responses from other objects located locally or remotely. Static and dynamic method invocations High-level language bindings Self-describing system Local/remote transparency Inter-ORB protocols Internet Inter-ORB Protocol (IIOP)

16 CS 501 Spring 2002 ORB: System View Object Request Broker Interface repository Dynamic invocation Client IDL stubs ORB interface Implementation repository Static skeletons Dynamic invocation Object adapter Client Object implementation

17 CS 501 Spring 2002 CORBA Services Naming service Event service Concurrency control service Transaction service Relationship service Externalization service Query service Life cycle service Persistence service Licensing service Properties service Security service Time service

18 CS 501 Spring 2002 Distributed Objects and the System Life-Cycle All large systems change with time. Dynamic binding of objects combined with polymorphism permits the addition of extra object types, incremental changes, etc. to be localized. Development environments change with time. Language bindings and IIOP permit changes. Production environments changes with time. Code can be reused in different environments.

19 CS 501 Spring 2002 Discussion of Pfleeger, Chapter 6 Format: State a question. Ask a member of the class to answer. (Sorry if I pronounce your name wrongly.) Provide opportunity for others to comment. When answering: Stand up. Give your name or NetID. Make sure the TA hears it. Speak clearly so that all the class can hear.

20 CS 501 Spring 2002 Question 1: Class boxes Here is a UML class box. Explain the three sections of this box. Bill Issue_date: Date price() taxes() add_bill (customer, amount)

21 CS 501 Spring 2002 Question 2: Packages Turn to Figure 6.18 on page 281. (a) What is the purpose of a package diagram? (b) Why do you think that some, but not all, of the lines have arrows? (c) What is the significance of the numbers on the line between the Parking and Parking Spaces classes?

22 CS 501 Spring 2002 Question 3: Use cases (a) What is a Use Case? (b) What is an extension to a Use Case? (c) At what stage of the Waterfall Model would you make use of Use Cases? (d) What have Use Cases to do with Object Oriented Design?

23 CS 501 Spring 2002 Question 4: A UML Diagram Explain the following diagram BookBorrower libMem: LibraryMember theCopy:Copy theBook:Book borrow(theCopy) okToBorrow borrow