Introduction to UML

Introduction to UML Software Engineering BIT-8 April, 16,2008

Agenda • Part 1: • Why modeling? • Introduction to Unified Modeling Language. • Uses of UML • Mapping Diagrams. • Part 2: • Use-Case Diagrams • Actors/Use-cases • Part 3: • Lab-Task: Case Study

Modeling • A model is a simplified representation of a complex reality. • Complex systems and software cannot be understood without properly modeling them. • Today, software are getting complex and consequently we need to understand them through modeling.

Modeling • In simple words, we need simpler representations for complex models and modeling is a mean for dealing with complexity. • A modeling method comprises a language and also a procedure for using the language to construct models. • Modeling is the only way to visualize your design and check it against requirements before you start to code.

Unified Modeling Language (UML) • UML is a notational system which is principally graphical and aims at modeling system using object oriented concepts. • UML is termed as a “Visual Modeling Language’. • Generally UML is used for modeling software systems. • UML consists of : • Views: shows different faces of the system and links with the process • Diagrams: are basically the graphs that explain the contents of view. • Model Elements: are contained within the diagrams.

Unified Modeling Language • UML is a complete language for capturing knowledge about a subject and then expressing that knowledge i.e. gathering requirements and then modeling those requirements. • Such modeling includes two phases : • Analysis • Design

Unified Modeling Language UML • Analysis Phase: • System is described by a set of requirements. • USE-CASE DIAGRAM • Design Phase: • It is tightly connected to the analysis phase, as it starts from the identification of requirements and continues up till the detailed specification of those requirements. • Class Diagrams • Interaction Diagrams • State Chart Diagrams • Deployment Diagrams

USE-CASE DIAGRAMS Software Engineering BIT-8

Use-Case Diagram • Use Case Diagram is used to describe the functionalities provided by a system and the users associated with that system. • The Use case diagram is used to identify the primary elements and processes that form the system. • The primary elements are termed as "actors" and the processes are called "use cases." • The Use case diagram shows which actors interact with each use case.

Use-Case Diagram • The main purpose of the use-case diagram is: • to help development teams visualize the functional requirements of a system • To help identify relationship of "actors" (human beings who will interact with the system) with essential processes • and understand the relationships among different use cases

Elements of a use-case diagram • Use-case diagrams contain the following elements: • Actors, which represent users of a system, including human users and other systems. • Use Cases, which represent functionality or services provided by a system to users.

Actor • Definition: • The outside entity which communicates with the system: • A Person (user) • An external system • Physical Environment • An Actor has a unique name and an optional description • Symbol: UML notation used to represent an actor

Actor (Example) • Consider the following scenario related to a “University Management System” : • In a university management system, a Student can submit the assignments, the instructor marks those assignments and then uploads the result. The Student is allowed to view the Results. • Now, by recalling the definition of actor, can you identify the actors in this System? • Student • Instructor

Actor (Example/2) Student Instructor Student is an external entity which interacts with the system. Student is a user of this system, as some services are used by it. Instructor is another external entity which interacts with the university management system. Student Instructor

Use-case • Represent functionality or services provided by a system to users. • It is a description of set of sequence of actions that a system perform that produces an observable result. • A use case represents a class of functionality provided by the system as an event flow. • Use cases describe the interaction between a primary actor and the system itself

Use-case • The use case technique is used in software and systems engineering to capture the functional requirements of a system. • Each use case describes how the actor will interact with the system to achieve a specific goal. • One or more scenarios may be generated from each use case, corresponding to the detail of each possible way of achieving that goal. • Symbol : UML notation used to represent a use-case

Use-case (Example) • Consider the same example again: • In a university management system, a Student can submit the assignments, the instructor marks those assignments and then uploads the result. The Student is allowed to view the Results. • Now, by recalling the definition of use-case, can you identify the use-cases in this System? • Submit Assignments • Mark Assignments • Upload Results • View Results

Use-case (Example/2) • The use-cases are linked with the functional requirements of this system. In this example : • Student submit the assignments. • Instructor marks the assignments. • Instructor upload the marks. • Student can view the marks. • It is now clear that how actors are interacting with different use-cases of this system. • Now, lets combine actors and use-cases in one diagram? Easy ?

Symbols in Use-Case Diagrams ACTOR USE-CASE INTERACTION: denotes set of messages exchanged among objects NOTES/COMMENTS

Use-Case Diagram (University Management System) SYSTEM BOUNDARY Submit Assignments Mark Assignments Student Upload Results View Results Instructor Package: University Management System

Extending Use-Case Diagram Software Engineering BIT-8

Lab-Exercise (Extracting Use-cases) 1 Hour Exercise

Use-Case Associations • Use case association is the relationship between use cases • Important types: • Extends • A use case extends another use case • Include • A use case uses another use case (“functional decomposition”)

<<Include>>: Functional Decomposition • A function in the original problem statement is too complex to be solved immediately. • What’s the Solution? • Describe the function as the aggregation of a set of simpler functions • The associated use case is decomposed into smaller use cases

<<include>> Example • The include association from Use Case A to Use Case B indicates that an instance of A performs all the behavior described in B • In <<include>> association, the base case cannot exist alone. It is always called with the supplier use case Base (A) <<include>> Supplier (B)

<<Extend>> Association for Use Cases • Problem: • The functionality in the original problem statement needs to be extended. • Solution: • An extend association from Use Case B to Use Case A indicates that B is an extension of A. <<extend>> A B

Example • Example: • The use case “ReportEmergency” is complete by itself , but can be extended by the use case “Help” for a specific scenario in which the user requires help • Note: In an extend association, the base use case can be executed without the use case extension <<extend>> Help ReportEmergency Field Officer

Lab-Exercise • Read the following case : • Identify the actors • Identify (extract ) the use cases • Construct a proper use-case diagram (with proper symbols & notations)

Case-Study • Consider the Library Management System of SEECS. A Student is allowed to issue books for a period of two weeks. Student can read newspapers/magazines in the library and can even access the databases for e-books. The Library Staff is responsible for maintaining the records of students and along with the issued books. The Staff marks an entry in the register whenever a student issue or return a book. A fine is charged on a student if he/she fail to return the book on time. The Librarian is there to manage the staff, check the records and prepare reports for DG/DEAN.

Introduction to UML