The College Of Applied Studies And Community Services Lecture 3 :Use cases II (UC description) Systems Analysis & Design Instructor: Nouf Aljaffan CT 1414 * Nouf Aljaffan 1 February 2012

Outline Concept of Use Case Description Levels of Use Case Description Reading and writing Use Case Descriptions CT 1414 * Nouf Aljaffan 2

Use Case Diagram of the Customer Support System Use Cases grouped into system modules Note: Same actor interacts with different modules CT 1414 * Nouf Aljaffan 3

Use Case Description Complements Use Case Diagram A breakdown of a single use case (e.g., sequence of steps included in the function “Look up item availability”); process logic included In contrast to Use Case Diagram, Use Case Description captures variations of a Use Case Example: “Create new order” can be done via phone+clerk and via Internet ordering – 2 scenarios (see slide 3) CT 1414 * Nouf Aljaffan 4

Level of Use Case Description Three levels of detail: UC* Brief description Summary of what system does in response to actor’s actions UC Intermediate description Shows steps in use case, if-then UC Full description Includes Brief description, expands intermediate description, shows scenarios CT 1414 * Nouf Aljaffan 5 * UC=Use Case

Brief Description of Create New Order Use Case CT 1414 * Nouf Aljaffan 6 Same description that is usually captured in initial Use Case Diagrams (“bird’s view” of system)

Intermediate Use Case Description CT 1414 * Nouf Aljaffan 7 Telephone Order Scenario for Create New Order Use Case

Full Use Case Description Superset of intermediate and brief descriptions (contains these) Consists of 11 compartments (we will use some) Shows steps (“Flow of Events”) broken down to the actor and the system side – useful! CT 1414 * Nouf Aljaffan 8

Full Use Case Description Telephone Order Scenario for Create New Order Use Case CT 1414 * Nouf Aljaffan 9 Computer System, Computer (steps encoded in software)

Use-Cases – Common Mistakes Complex diagram No system No actor Too many user interface details “User types ID and password, clicks OK or hits Enter” Very low goal details User provides name User provides address User provides telephone number … CT 1414 * Nouf Aljaffan 10

Writing Use Case Descriptions 1.Select a use case 2.Write abbreviated full description (Use case name, Scenario (if any), Business Event, Actors, Flow of steps, Exception conditions) 3.For figuring Flow of steps, - Keep in mind general system model: Input-Processing-Output - Steps should be at nearly the same level of abstraction (each makes nearly same progress toward use case completion) 4.For figuring exception conditions, focus on if-then logic. CT 1414 * Nouf Aljaffan 11

Method of Modeling Bottom-up Process Starting with throwing all scenarios on the page, and then combining them: Top-down Process Starting with an overview of the system, and then splitting Use- cases CT 1414 * Nouf Aljaffan 12 File actions Formatting actions Viewing Actions print save Bullets format load Save as preview Font format Paragraph format

Combining Processes Number Limit: The diagram should have between 3 to 10 base use-case. No more than 15 use cases (base + included + extending). Abstraction: All use-cases should be in similar abstraction levels. Size: Use cases should be described in half a page or more. Interaction: Use-cases which are carried out as part of the same interaction. CT 1414 * Nouf Aljaffan 13 UC

Dividing Processes Size: If a use-cases takes more than a page, consider include/extend Weak dependency: If the dependency between two parts of a use-case is weak, they should be divided. CT 1414 * Nouf Aljaffan 14 UC

More Guidelines Factor out common usages that are required by multiple use cases If the usage is required use > If the base use case is complete and the usage may be optional, consider use > A use case diagram should: contain only use cases at the same level of abstraction include only actors who are required CT 1414 * Nouf Aljaffan 15