Lecture05

Object Oriented Software Modeling and Design CE 350 Abdel-Karim Al-Tamimi, Ph.D. [email_address] http://faculty.yu.edu.jo/altamimi Al-Tamimi 2011 ©

Overview Documenting a Use-case Diagram Developing a Use-case Diagram Al-Tamimi 2011 ©

Documenting Use-Cases A use-case is a description of what a system is used for, and who uses it, without providing details of how it performs its functions A use-case description serves as an agreed description between the user and the system designer on the flow of events that would happen when a use case is invoked A use-case description is explained and elaborated through scenarios (a set of sequences of actions) Each of these scenarios is simply an instance of the use-case Use-cases are text documents not diagrams Al-Tamimi 2011 ©

Documenting Use-Cases Al-Tamimi 2011 ©

Importance of Use-Cases The use case model is not only useful for requirements specification but also for planning the work in different phases of the system development life cycle Since the use case model should be understandable by both the system developer and the user, it is quite natural to plan the development of the system by scheduling the completion dates of the use cases in the use case model Al-Tamimi 2011 ©

Use-Case Formats Use-cases are written in different formats and levels of formality: Brief : usually a one paragraph summary, usually the main success scenario Casual : informal paragraph format. Multiple paragraphs that cover various scenarios Fully dressed : all steps and variations are written in detail, and there are supporting sections, such as preconditions and success guarantees Al-Tamimi 2011 ©

Use-Case Template Example Part 1 Al-Tamimi 2011 © Use case name Name of the use case Use case ID ID of the use case Super use case The name of the generalized use case to which this use-case belongs Actor(s) The name of the actor(s) who participates in the use case Brief description A description showing how this use case adds value to the organization, that is, what the purpose or role of this use case is in enabling the actors to do their job Preconditions The conditions that must be satisfied before this use case can be invoked Post-conditions The conditions that will be established as a result of invoking this use case sucessfully

Use-Case Template Example Part 2 Al-Tamimi 2011 © Flow of events A step-by-step description of the interactions between the actor(s) and the system, and the functions that must be performed in the specified sequence to achieve a user goal Alternative flows and exceptions Major alternatives or exceptions that may occur in the flow of events Priority The development priority of this use case Non-behavioral requirements The non-functional requirements of the system such as hardware and software platform requirements, performance, security, … etc Assumptions All the assumptions made about the use case Issues All outstanding issues regarding the use case Source Reference materials relevant to the use case

Use-Cases Prioritization The following factors typically increase the priority ranking of a use case: Architectural significance of the use case Use of new and untested technologies Problems which require substantial research effort Great improvement in efficiency (or revenue) of the business process; and Use cases that support major business processes Al-Tamimi 2011 ©

Packages Packages should be used where appropriate to make the use-case diagram more easily understood Use cases that form a natural grouping should be organized into packages Al-Tamimi 2011 ©

Developing an initial use case model Developing the problem statement Identifying the major actors and use-cases Creating an initial use-case diagram Describing briefly the use-cases (with initial descriptions) Identifying/refining candidate business (domain) classes using textual analysis Refining the use case model Developing base use-case descriptions Structuring Use-Cases : Iteratively elaborating on the base use-case descriptions and determining the extend , include and generalization relationships Developing instance scenarios Prioritizing use-cases Developing Use-Cases Steps Al-Tamimi 2011 ©

Developing An Initial Use-Case Model Developing the problem statement Identifying the major actors and use-cases Creating an initial use-case diagram Describing briefly the use-cases (with initial descriptions) Identifying/refining candidate business (domain) classes using textual analysis

Step 1 : Developing the Problem Statement The chief executive officer of a mail order company is interested in computerizing the company’s business process in order to improve operational efficiency. The major business activities of the company can be briefly described as follows: A customer registers to become a member by filling in the membership form and mailing it to the company. A member who has not been active (no transactions) for a period of one year will be removed from the membership list and he/she needs to apply for reinstatement of the lapsed membership Al-Tamimi 2011 ©

Step 1 : Developing the Problem Statement A member should inform the company of any change in personal details, such as home address, telephone numbers, etc A member can place an order by filling out a sales order form and faxing it to the company or by phoning the Customer Service Assistant with the order details The Customer Service Assistant checks the validity of membership and then enters the sales order information into the system Al-Tamimi 2011 ©

Step 1 : Developing the Problem Statement The Order Processing Clerk checks the availability of the ordered items and, if they are available, holds them for the order. When all the ordered items are available, the Order Processing Clerk will schedule their delivery. The Inventory Control Clerk controls and maintains an appropriate level of stock and is also responsible for acquiring new items. Al-Tamimi 2011 ©

Step 1 : Developing the Problem Statement If there is a problem with an order, the member will phone the Customer Service Assistant , who will then take appropriate action to follow up the particular sales order Members may return defective goods within 30 days and get their money back The system will record the name of the staff member who handles the transaction for future follow up action Al-Tamimi 2011 ©

Step 2-a : Identifying the Major Actors Actors from the client point of view: Customer Service Assistant Order Processing Clerk Inventory Control Clerk Actor Specification: Al-Tamimi 2011 © Actor name: Order Processing Clerk Description: The Order Processing Clerk is responsible for processing sales orders, submitting reorder requests, requesting necessary deposits from members and scheduling the delivery of the goods to members

Step 2-b : Identifying the Use-Cases The following questions may be useful in collecting information from users: What are the main tasks carried out by each actor? What data are manipulated and processed by the system? What problems is the system going to solve? What goals does an actor want to achieve using the system? What are the major problems with the current system and how could the proposed system simplify the work of the user? Al-Tamimi 2011 ©

Step 2-b : Identifying the Use-Cases Check order status Place order Handle goods return Update membership record Archive membership Register new member Process order Schedule delivery Order goods Receive goods Deliver goods Al-Tamimi 2011 ©

Step 3 : Creating an initial use-case diagram Al-Tamimi 2011 ©

Step 4 : Describing briefly the Use-Cases An Initial Use Case Description of the Schedule Delivery Use-Case : Al-Tamimi 2011 © Use case: Schedule Delivery Use case ID: UC-300 Actor: Order Processing Clerk Description: The Order Processing Clerk selects an order from the list of filled sales orders. The system displays the sales order details, and the member’s telephone number and address are displayed. The Order Processing Clerk enters the delivery date and time after talking with the member over the phone. The system records the delivery date and time in a dispatch request to the delivery team.

Step 4 : Describing briefly the Use-Cases An Initial Use Case Description of the Check Order Status Use-Case: Al-Tamimi 2011 © Use case: Check Order Status Use case ID: UC-400 Actor: Customer Service Assistant Description: The Customer Service Assistant enters the ID of the member. The Customer Service Assistant selects a sales order of the member. The system displays the status of the sales order.

Step 5 : Identifying/refining candidate business (domain) classes using textual analysis To identify the objects and classes, perform a textual analysis to extract all nouns and noun phrases from the problem statement The following categories are more likely to represent objects: Tangible things (e.g. classroom, playground) Conceptual things (e.g. course, module) Events (e.g. test, examination, seminar) Outside organizations (e.g. publisher, supplier) Roles played (e.g. student, teacher, principal) Other systems (e.g. admission system, grade reporting system) Al-Tamimi 2011 ©

Step 5 : Identifying/refining candidate business (domain) classes using textual analysis Al-Tamimi 2011 © Use case: Schedule Delivery Use case ID: UC-300 Actor: Order Processing Clerk Description: The Order Processing Clerk selects an order from the list of filled sales orders . The system displays the sales order details, member’s telephone number and address . The Order Processing Clerk enters the delivery date and time after talking with the member over the phone . The system records the delivery date and time in a dispatch request to the delivery team .

Step 5 : Identifying/refining candidate business (domain) classes using textual analysis Al-Tamimi 2011 ©

Refining the Use-Case Model Developing base use-case descriptions Structuring Use-Cases : Iteratively elaborating on the base use-case descriptions and determining the extend , include and generalization relationships Developing instance scenarios Prioritizing use-cases

Basic Flow List the basic events that will occur when this use case is executed Include all the primary activities that the use case will perform Be fairly descriptive when defining the actions performed by the actor and the response of the use case to those actions This description of actions and responses are your functional requirement This will be the basis for writing the test case scenarios for the system Al-Tamimi 2011 ©

Alternative Flow Any subsidiary events that can occur in the use case should be listed separately Each such event should be completed in itself to be listed as an alternative flow If there are too many alternatives flows, you need to revisit your design to make it simpler, or break the use case into smaller units Al-Tamimi 2011 ©

Alternative Flow One way to look at it  they are really all the same thing by different names: Optional flows implies that the behavior is optional and doesn't always need to be performed Alternative flows implies some sort of alternative decision is taken Exception flows implies that something other than the ordinary has occurred Al-Tamimi 2011 ©

Basic vs. Exception vs. Alternative Flows Basic Flow is the normal flow of action in an application. For example, in the login page after entering user name and password the next screen should appear is the basic flow Exception flow are the activities in case of the exception thrown. They are the flow of events which will happen in case of the error Alternate flow are the alternative actions that can be performed. For example in the login page the alternative flow will be checking the existence of the user name entered Al-Tamimi 2011 ©

Basic vs. Alternative vs. Exception Flows Al-Tamimi 2011 © Basic Flow Alternate Flow 1 Alternate Flow 2 Alternate Flow 3 Alternate Flow 4 Exception Flow 1 Exception Flow 2 Exception Flow 3

Step 1 : Developing base use-case descriptions Al-Tamimi 2011 © Use case name Place Order Use case ID UC-100 Super use case The name of the generalized use case to which this use case belongs. Actor(s) Customer Service Assistant Brief description A Customer Service Assistant places an order and then submits it for processing. Preconditions The member must have registered with the system. Post-conditions The Customer’s order will be directed to the order processing department for processing.

Step 1 : Developing base use-case descriptions Al-Tamimi 2011 © Flow of events The Customer Service Assistant finds the member’s record by entering the member’s ID or name. The system displays a list of members which match the information entered by the Customer Service Assistant. The Customer Service Assistant selects the required member record. The system displays the details of the member. The Customer Service Assistant selects “Place Order”. A new order form and order ID are then generated and displayed. The Customer Service Assistant selects items from the catalog and adds them to the order. The Customer Service Assistant submits the order for processing. The system records the order and forwards it to the Order Processing Clerk.

Step 1 : Developing base use-case descriptions Al-Tamimi 2011 © Alternative flows and exceptions At any time the Customer Service Assistant can decide to suspend the ordering process and come back to it later, or to cancel the order. Priority High Non-behavioral requirements The system should be able to handle 20,000 new orders per day. Assumptions Issues Is there any limit on the amount of an order? Source User Interview Memo 21, 8/9/01

Step 2 : Structuring Use-Cases Al-Tamimi 2011 © Use case name Place Order Use case ID UC -100 Super use case Actor(s) Customer Service Assistant Brief description A Customer Service Assistant places an order and then submits it for processing. Preconditions The member must have registered with the system. Post-conditions The Customer’s order will be directed to the order processing department for processing. Flow of events Include ( Find Member Record ). The Customer Service Assistant selects “Place Order”. A new order form and order ID are then generated and displayed. The Customer Service Assistant selects items from the catalog and adds them to the order. The Customer Service Assistant submits the order for processing. The system records the order and forwards it to the Order Processing Clerk.

Step 2 : Structuring Use-Cases Al-Tamimi 2011 © Use case name Find Member Record Use case ID UC-10 Brief description A member record is requested. Post-conditions A membership record is returned. Flow of events The Customer Service Assistant finds the member record by entering the member’s ID or name. The system displays a list of members which match the information entered by the Customer Service Assistant. The Customer Service Assistant selects the required member record. The system then displays the details of that member. Alternative flows and exceptions No member record is found for the customer.

Step 3 : Developing Instance Scenarios A use case specifies all possible ways of using a system functionality to achieve a user goal Sometimes, it is necessary to write some examples (instance scenarios) to illustrate the execution of a complex use case Instance scenarios are easier for the user to understand, and they are very useful for clarifying any ambiguity in the use case description The instance scenarios can also serve as test cases for system testing Al-Tamimi 2011 ©

Step 3 : Developing Instance Scenarios Al-Tamimi 2011 © Parent use case name Place Order Parent use case ID UC-100 Instance name A sales order form is received but the membership number is missing. Instance ID UCIS-100-1 Environmental conditions and assumptions The name (Peter Chan) and signature of the member are available in the system. Inputs A sales order form

Step 3 : Developing Instance Scenarios Al-Tamimi 2011 © Instance flow description The Customer Service Assistant enters “Peter Chan” to find the member record. The system then displays a list of members which match the member’s name. The Customer Service Assistant repeatedly selects a member record. The system displays the signature of the member when a member record is selected. The Customer Service Assistant selects “Place Order”. A new order form and order ID are then generated and displayed. The Customer Service Assistant selects items from the catalog and adds them to the order. The Customer Service Assistant submits the order for processing. The system records the order and forwards it to the Order Processing Clerk. Outputs The sales order is placed.

Step 4 : Prioritizing Use-Cases Al-Tamimi 2011 © Priority Rank Use Case Reason High Process Order Directly improves the efficiency of the business process and affects the system architecture. High Place Order Same as above High Find Member Record Included as part of the Place Order use case. Medium Order Goods Ordering goods is less often than processing order but still is one of the major business processes. Medium Deliver Goods Can improve the control of stock level. Low Update Membership Record Small impact on the system architecture. Low Register New Member Same as above.

Resources Object Oriented Technology, By Tsang chapter 3 Tsang slides Chapter 6, Applying UML and Patterns Al-Tamimi 2011 ©

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