Software Architectures

Software Architectures
Dr. M.E. Fayad, Professor Computer Engineering Department, Room #283I College of Engineering San José State University One Washington Square San José, CA © M.E. Fayad SJSU -- CmpE

Lesson 4-2: Use Case Diagrams
© M.E. Fayad SJSU – CmpE --- M.E. Fayad

3 Lesson Objectives Overview of Previous Lecture
Use Case Models and Diagrams Notation Discuss the following: What is use case modeling? Use Case Modeling -- Core concepts Use Case Diagram tour When to model use cases Use Case Modeling tips Use Case Templates Examples: Library & University Registration 3 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case Modeling: Core Elements
4 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case Modeling: Core Relationships (1)
<<extend>> 5 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case Modeling: Core Relationships (2)
<<include>> Multiplicities are missing! 6 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

7 Use Case Diagram Tour Shows use cases, actor and their relationships
Use case internals can be specified by text and/or interaction diagrams Kinds use case diagram use case description 7 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

8 When to model use cases Model user requirements with use cases.
Model test scenarios with use cases. If you are using a use-case driven method start with use cases and derive your structural and behavioral models from it. If you are not using a use-case driven method make sure that your use cases are consistent with your structural and behavioral models 8 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case Modeling Tips Make sure that each use case describes a significant chunk of system usage that is understandable by both domain experts and programmers When defining use cases in text, use nouns and verbs accurately and consistently to help derive objects and messages for interaction diagrams Factor out common usages that are required by multiple use cases If the usage is required use <<include>> If the base use case is complete and the usage may be optional, consider use <<extend>> A use case diagram should contain only use cases at the same level of abstraction include only actors who are required Large numbers of use cases should be organized into packages 9 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Actors (1) An actor is someone or some thing that must interact with the system under development Registrar Professor Student Billing System 10 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Actors (2) An actor represents a coherent set of roles that users of use cases play when interacting with the use cases Typically, an actor represents a role that a human, a hardware device, or even another system plays with a system 11 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Cases (1) A use case is a pattern of behavior the system exhibits Each use case is a sequence of related transactions performed by an actor and the system in a dialogue It describes what a system does but NOT how it does it 12 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Cases (2) A use case is a description of a set of sequences of actions, including variants, that a system performs to yield an observable result of value to an actor Each use case must have a name that distinguishes it from other use cases 13 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

14 Use Cases (3) Actors are examined to determine their needs
Registrar -- maintain the curriculum Professor -- request roster Student -- maintain schedule 14 Maintain Curriculum Request Course Roster Maintain Schedule © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case Relationships (1)
Can organize use cases by specifying relationships among them. Generalization Include Extend 15 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Generalization Child use case inherits the behavior and meaning of the parent use case Child use case may add to or override the behavior of its parent Child use case may be substituted any place the parent use case appears 16 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Include Base use case explicitly incorporates the behavior of another use case at a location specified in the base Use an include relationship to avoid describing the same flow of events several times by putting the common behavior in a use case of its own 17 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

<<include>> Register for courses <<include>> Logon validation 18 Maintain curriculum © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Extend An extend relationship between use cases means that the base use case implicitly incorporates the behavior of another use case at a location specified indirectly by the extending use case Use an extend relationship to model the part of a use case the user may see as optional system behavior 19 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Included Use Case Super Use Case <<include>> <<extend>> generalization Extending Use Case 20 Sub Use Case © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Fig. 3-45, UML Notation Guide © M.E. Fayad SJSU – CmpE --- M.E. Fayad

X 22 Fig. 3-46, UML Notation Guide © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case Model UC model = Use Cases + System Boundary + Actors (outside the system boundary) 23 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

What is use case modeling?
use case model: a view of a system that emphasizes the behavior as it appears to outside users. A use case model partitions system functionality into transactions (‘use cases’) that are meaningful to users (‘actors’). 24 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case Diagram (1) Use case diagrams are created to visualize the relationships between actors and use cases Student Registrar Professor Maintain Schedule Maintain Curriculum Request Course Roster Billing System 25 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case Diagram (2) A use case diagram is a diagram that shows a set of use cases and actors and their relationships. Commonly contain Use cases Actors Dependency, generalization, and association relationships 26 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

27 Use Case Diagram (3) SJSU – CmpE --- M.E. Fayad

The Use Case Model We must now identify the users of the system and the tasks they must undertake with the system. The details of the use case should be documented, using a Use Case Template. There are many different use case templates Show a few!! 34 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case Template & Example: Change Flight
Use Case Name: Change flight Actors: traveler, client account db, airline reservation system Preconditions: Traveler has logged on to the system and selected ‘change flight itinerary’ option Basic course System retrieves traveler’s account and flight itinerary from client account database System asks traveler to select itinerary segment she wants to change; traveler selects itinerary segment. System asks traveler for new departure and destination information; traveler provides information. If flights are available then … System displays transaction summary. Alternative courses If no flights are available then … 35 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

36 My Use Case Template Use Case Template
1/16/2019 My Use Case Template Use Case Template PACKAGE: _________________ [Description (an over view of the package)]. USE CASES: [A package will have one or more Use Cases]. Use Case No.: [1.1] Use Case Title: [A descriptive title] [Ex. adding a new patient, or adding a new role]. Actors: _______, _______, _______, _______. [Any users of the Use Case, ex. human, machine, other systems or subsystems]. Corresponding Roles: _______, _______, _______, _______. [There is a different role per actor in every Use Case]. Classes: _______, _______, _______, _______. [List all the classes within the Use Case Description]. Corresponding Attributes and Behaviors: Enduring Business Themes (EBT): _______, _______, _______ Business Objects (BO): _______, _______, _______, _______. Industrial Objects (IO): _______, _______, _______, _______. [This represents a clear classification of all the classes within the use case description]. Description of the Use Case: [Describes the data flow and the logic flow of the Use Case]. Alternatives: The details of the use case should be documented, using a Use Case Template. 36 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Case Study 1: Library System
You have been contracted to develop a computer system for a university library. The library currently uses a 1960s program, written in an obsolete language, for some simple bookkeeping tasks, and a card index, for user browsing. You are asked to build an interactive system which handles both of these aspects online.* 37 *Example from: “Using UML”, by: Pooley and Stevens © M.E. Fayad SJSU – CmpE --- M.E. Fayad

38 First Step! Time to start gathering the user requirements.
Different users will have different, sometimes conflicting priorities Users will not, necessarily know what they want It is very possible to miss something vital The managers do not always know what the users have to do Users can be, and frequently are, hostile. Why? What can be done about it? 38 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Copyright © 1997 by Rational Software Corporation
1/16/2019 Documenting Use Cases A flow of events description is created for each use case Written from an actors point of view Details what the system must provide to the actor when the use case is executed Typical contents How the use case starts and ends Normal flow of events Alternate flow of events Exceptional flow of events 39 Copyright © 1997 by Rational Software Corporation © M.E. Fayad SJSU – CmpE --- M.E. Fayad 16

Actors An actor is someone or something that must interact with the system under development BookBorrower Browser Librarian JournalBorrower © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Cases Actors are examined to determine their needs BookBorrower
Checkout and return books Browser locate and peruse items of interest Librarian maintain order and accountablility JournalBorrower checkout and return journals Checkout Journal Checkout Book Return Book © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case Description The usual course through the system when actor is using the system is called the basic course. Other courses would be modeled as extending Use Cases. An example of a basic course would be: Borrow copy of book A BookBorrower presents a book. The system checks that the potential borrower is a member of the library, and that s/he does not already have the maximum permitted number of books on loan. This maximum is six unless the member is a staff member, in which case it is 12. If both checks succeed, the system records that this library member has this copy of the book on loan. **Example from: “Using UML”, by: Pooley and Stevens 42 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case Diagram for the first iteration
43 *Example from: “Using UML”, by: Pooley and Stevens © M.E. Fayad SJSU – CmpE --- M.E. Fayad

What Requirements would an ideal system satisfy?
Books and Journals: The library contains books and journals. It may have several copies of a given book. Some of the books are for short term loans only. All other books may be borrowed by any library member for three weeks. Only members of staff may borrow journals. Members of the library can normally borrow up to six items at a time, but members of staff may borrow up to 12 items at one time. New books and journals arrive regularly, and are sometimes disposed of. The current year’s journals are sent away to be bound into volumes at the end of each year.* 44 *Example from: “Using UML”, by: Pooley and Stevens © M.E. Fayad SJSU – CmpE --- M.E. Fayad

What Requirements would an ideal system satisfy?
Borrowing: It is essential that the system keep track of when books and journals are borrowed and returned, since the current system already does that. The new system should produce reminders when a book is overdue. There may in future be a requirement for users to be able to extend the loan of a book if it is not reserved. Browsing: The system should allow users to search for a book on a particular topic, by a particular author, etc., to check whether a copy of the book is available for loan, and if not, to reserve the book. Anyone can browse in the library.* 45 *Example from: “Using UML”, by: Pooley and Stevens © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Cases for the library
46 *Example from: “Using UML”, by: Pooley and Stevens © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Case Study 2: University Registration
The ESU University wants to computerize their registration system The Registrar sets up the curriculum for a semester One course may have multiple course offerings Students select 4 primary courses and 2 alternate courses Once a student registers for a semester, the billing system is notified so the student may be billed for the semester Students may use the system to add/drop courses for a period of time after registration Professors use the system to receive their course offering rosters Users of the registration system are assigned passwords which are used at logon validation 47 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

1/16/2019 Use Cases Actors are examined to determine their needs Registrar maintain the curriculum Professor request roster Student maintain schedule Billing System receive billing information from registration Maintain Schedule Maintain Curriculum Request Course Roster Copyright © 1997 by Rational Software Corporation © M.E. Fayad SJSU – CmpE --- M.E. Fayad 15

Maintain Curriculum: Flow of Events (description)
1/16/2019 Maintain Curriculum: Flow of Events (description) This use case begins when the Registrar logs onto the Registration System and enters his/her password. The system verifies that the password is valid (E-1) and prompts the Registrar to select the current semester or a future semester (E-2). The Registrar enters the desired semester. The system prompts the professor to select the desired activity: ADD, DELETE, REVIEW, or QUIT. If the activity selected is ADD, the S-1: Add a Course subflow is performed. If the activity selected is DELETE, the S-2: Delete a Course subflow is performed. If the activity selected is REVIEW, the S-3: Review Curriculum subflow is performed. If the activity selected is QUIT, the use case ends. 50 Copyright © 1997 by Rational Software Corporation © M.E. Fayad SJSU – CmpE --- M.E. Fayad 17

1/16/2019 Use Case Model Use case diagrams are created to visualize the relationships between actors and use cases Request Course Roster Professor Student Maintain Schedule Billing System Maintain Curriculum Registrar Copyright © 1997 by Rational Software Corporation © M.E. Fayad SJSU – CmpE --- M.E. Fayad 18

Uses and Extends Use Case Relationships
1/16/2019 Uses and Extends Use Case Relationships As the use cases are documented, other use case relationships may be discovered A uses relationship shows behavior that is common to one or more use cases An extends relationship shows optional behavior Register for courses <<uses>> Logon validation Maintain curriculum Copyright © 1997 by Rational Software Corporation © M.E. Fayad SJSU – CmpE --- M.E. Fayad 19

Possible Problems with Use Cases
Use Cases emphasize ordering. This can be considered to be incompatible with object technology. Over modeling – Leads to requirement inflation. 53 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

54 Cautions Do not invent requirements!
Use cases are about the user’s requirements, not about what you, as the designer might think that the system could usefully do! 54 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Sample Use Case from Philips Project (1)
Use Case No.: 1.1.1 Use Case Title: Find Candidate Actors: Registrar Roles: Data Entry Clerk (Registrar), Classes: IDSession, PersonProfile, PersonIdentifier, PersonTraits , CandidateListGenerator, DataManager Enduring Business Themes: (EBT): identity, security, Business Objects: IDSession, IDManager, DataManager, PersonIdentifier Industrial Objects: CandidateList, PersonTraits, PersonProfiles, SecurityManager, TraitGatekeeper 55 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Description of the Use Case: 1. The Registrar enters the information about a person into the System. 2. IDSession clears the request with Security. 3. The System tells the Person-Identifier to search for candidates. 4. The Person-Identifier gives the request to its DataManager 5. The DataManager determines a list of candidates, using its CandidateListGenerator and its set of PersonProfiles and returns it to the System. 6. The Registrar chooses the candidate from the list that represents the person. 56 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case No.: 1.2.1 Use Case Title: Register New ID Actors: Registrar Roles: Data Entry Clerk (Registrar), Classes: IDSession, IDManager, PersonProfile, PersonTraits, CandidateList, PersonIdentifier Enduring Business Themes (EBT): identity, security Business Objects (BO): IDSession, IDManager, PersonIdentifier Industrial Objects (IO): PersonProfile, PersonTraits, CandidateList 57 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Description of the Use Case: 1. The Registrar enters the information about a person into the IDSession. 2. The IDSession has security clear the request. 3. The IDSession has the PersonIdentifier search for candidates. 4. The Person-Identifier determines that no candidates fit the criteria. 5. The Person-Identifier gives this information to the system. 6. The informs the Registrar that no candidates exist. 7. System asks the Registrar if the person should be added as new. 8. Registrar tells System to add new person. 9. System sends traits to ID-Manager. 10. ID-Manager creates a new profile. 58 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Exceptional Flow of Events 01: If any of the identifying information entered by the Registrar is incomplete or invalid the system displays corresponding error message(s). The system will not validate the New Person until all identifying information is made available. Exceptional Flow of Events 02: In case the system determines that one or more of the identifying information for a person matches one or more person(s) already in the system the Registrar is displayed with a screen listing all the person(s) meeting the search criteria. The Registrar is then given the opportunity to either create the person in the system with a new ID or pick one from the selection list. 59 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Use Case No.: 1.3.1 Use Case Title: Get Patient Profile using Patient ID Actors / Roles: Nurse, Patient, and Profile Access Classes: Enduring Business Themes (EBT): Diagnosis, Customer Service and Complete Medical History Business Objects (BO): Profile Access, Identify Person and Identity Industrial Objects (IO): Identity Access 60 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Description of the Use Case: 1. The Nurse enters the Person ID for the person. 2. The Person Identification system determines the validity of the Person ID. 3. The Get Profile System returns the profile the specified Person ID. Exceptional Flow of Events 01: If the Person ID is invalid an error message is displayed. The nurse then can decide either to search the system with person identification information or redirect the person to a Registrar. 61 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

64 Multiplicities (1) Association One to Many
* * One to Many 1 Association Directed association is a one-way association, in which one side knows the other, but not vice versa. Multiplicity Specification: 1 exactly one 0, 1 zero or one 0..4 between zero and four 3, 7 either three or seven 64 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

65 Multiplicities (2) More multiplicity specifications:
0..* greater than or equal to zero (default) * many 1..* greater than or equal to one 0..3, 7, 9..* between zero and three, or exactly seven, or greater than or equal to nine. 65 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Samples of Use Case Diagrams (1)
supply Retailer Wholesaler * sale 66 A supply activity consists of many sales. © M.E. Fayad SJSU – CmpE --- M.E. Fayad

deliver, pay sale 1 * 1 Retailer Wholesaler order 67 A sale activity consists of order and deliver. © M.E. Fayad SJSU – CmpE --- M.E. Fayad

sale Different kinds of sales & their constituent actions saleByPrice saleByQty saleBySupply salePrice 68 pay accept order reqPay deliver © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Discussion Questions 1. Define: use case model, a use case, use case diagrams, and, actors 2. T/F a. A use case is a pattern of behavior the system exhibits. b. A use case describes how the system does it but NOT what a system does. c. Use case diagrams are created to visualize the behavior between actors and use cases d. Use cases are about user’s requirements not about what you might think as a designer that the system could usefully do. 69 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Questions for the Next Lecture
CRC Cards Existing CRC Cards My CRC Cards How to create with CRC Cards 70 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

Tasks for Next Lecture Task 1: Problem Statement for team projects are needed (see sample problems on OOPSLA – DesignFest). This is due on the third week of the semester. Task 2: Identify the team members of your team. Select a team name and me, the team name, team’s members’ names, their s, phone numbers -- Immediately. Task 3: Think about extra assignments and writing essays. me if you like to start right away. Please note that problem statements must be submitted electronically as MS Word format. 71 © M.E. Fayad SJSU – CmpE --- M.E. Fayad

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