Actors and use casesUse-case diagramBrief notationPrioritizationFully dressed notation

RequirementsFunctional requirements Use-cases

What is a use case?

A use-case describes a working procedure for a specific actor/user of an IT system. A use-case is used to show the interaction between actor and IT system Functional requirements as use-cases outline, in what way the IT system are going to support the user

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Good or Bad Use-cases?

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Good or bad?Administration of booksRegister the title of a bookLoan of bookUpdate reservationDelete reservation

Check: Are all tasks included?– Are all actor tasks

described?– Are critical tasks

included?– Can all data be

created, read, updated and deleted (CRUD)?

• Criteria:– Completed; goal fulfilled; coffee break– Small create, read, update and delete tasks are

gathered in one description (CRUD)

What is an actor?

An actor is something with behaviour that interacts with the IT system:

Person identified as a user role, e.g. cashier, salesman, stock employeeAnother computer systemA device e.g. a temperature sensor

Primary actor: Has user goals fulfilled through use-case

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Use case diagram

Use cases from the event table is displayed in a UML use case diagramUse case diagram is a graphic model of the system's functionality and communication with the stakeholdersincludes:

Use casesActorsAssociations between use cases and the actor(s) who interact with the use casedelimitation

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Use case diagram for customer - order

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Small use cases can be assembled in CreateReadUpdateDelete (CRUD) use-cases

Description formats for use cases

Overall textual descriptions in a short summarized form (customer-facing)

Brief: textual description of a happy days scenarioCasual: variations of happy days scenario

Detailed descriptions of the "expanded" form - fully dressedThe steps in the use case and variations thereof are described in detail

A graphical representation of the interaction of the use case in a system sequence diagram - SSD (in a later session)All use cases described in brief and / or causal. Only the critical described fully dressed with associated solid state and contracts

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Use case description, BriefTemplate for brief description:

Use case: Name of the use caseDescription: An overall but complete description of who initiates the use case, the expected system actions and responses of this that adds value to an actor

Input to the system actions retrieved from the event table: Steps in use case

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Use-case description Casual

In addition to the brief form there can be added alternative scenarios in the Causal formatExamples of alternative scenarios for the use-case: Register Order:

If the goods are sold the system indicates when new products are expected home, so the customer can be informedIf the customer wishes to pay immediately ......

.......

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Prioritazation af use-cases

According UP designing, implementation and testing is done in small chunks through a number of iterations (steps)The highest priority and most complex use-case is analysed, designed and coded in the first iterations (so one must assume that the rest also can be made)The steps in development of use-cases are:1. Use cases identified and they appear in a UML use-case diagram2. Then, they are described in brief or casual form.3. On this basis, use cases are prioritized (based on architecture-

related importance, risks and business value), and then the most important are analysed for the design of prototypes and "fully dressed" descriptions.

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Use-case description: ”Fully dressed”

Detail storyline in use-case in a number of steps (flow of events) consisting of:

Actor action<-> System response

Add actor, pre- and post-conditionsUse essential and black box style Brief- and/or casual descriptions and mock ups are used as the basis for the fully dressed descriptions.

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Example: Use case: Register OrderFlow of events in fully dressed description1. Use-case starts with a customer inquiry over the telephone to order goods2. Shop assistant begins a new order

the system creates a new order

3. Shop assistant Specifies the ID of the desired products4. The system returns the item description, price, sub total and running total5. Shop assistant adds the desired number of items

1. The system adds the items6. Steps 4-7 are repeated until all items are added7. Shop assistant specify delivery information8. The system validates the data and record customer9. Shop assistant completes order10. The System saves the order

11. Shop assistant request for an order form and invoice12. The system prints a confirmation

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