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| version="1.0.0"> |
| <mainDescription><h3>
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| Explanation
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| </h3>
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| <p>
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| A use-case model is a model of how different types of users interact with the system to solve a problem.&nbsp; As such,
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| it describes the goals of the users, the interactions between the users and the system, and the required behavior of
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| the system in satisfying these goals.
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| </p>
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| <p>
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| A use-case model consists of a number of model elements.&nbsp; The most important model elements are: use cases, actors
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| and the relationships between them.
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| </p>
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| <p>
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| A use-case diagram is used to graphically depict a subset of the model to simplify communications.&nbsp; There will
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| typically be several use-case diagrams associated with a given model, each showing a subset of the model elements
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| relevant for a particular purpose.&nbsp; The same model element may be shown on several use-case diagrams, but each
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| instance must be consistent.&nbsp; If tools are used to maintain the use-case model, this consistency constraint is
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| automated so that any changes to the model element (changing the name for example) will be automatically reflected on
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| every use-case diagram that shows that element.
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| </p>
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| <p>
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| The use-case model may contain packages that are used to structure the model to simplify analysis, communications,
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| navigation, development, maintenance and planning.
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| </p>
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| <p>
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| Much of the use-case model is in fact textual, with the text captured in the&nbsp;<a class="elementLink"
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| href="./../../../openup/guidances/templates/uc_specification.html" guid="_0cpNwMlgEdmt3adZL5Dmdw">Use-Case
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| Specification</a>s that are associated with each use-case model element.&nbsp;These specifications describe the flow of
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| events of the use case.
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| </p>
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| <p>
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| The use-case model serves as a unifying thread throughout system development. It is used as the primary specification
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| of the functional requirements for the system, as the basis for analysis and design, as an input to iteration planning,
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| as the basis of defining test cases and as the basis for user documentation&nbsp;&nbsp;
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| </p>
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| <h3>
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| Basic model elements
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| </h3>
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| <p>
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| The use-case model contains, as a minimum, the following basic model elements.
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| </p>
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| <h4>
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| Actor
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| </h4>
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| <p>
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| A model element representing&nbsp;each actor. Properties include the actors name and brief description. See&nbsp;<a
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| class="elementLinkWithType" href="./../../../openup/guidances/concepts/actor.html"
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| guid="_zGqO0MDpEduTGJ8i4u8TMw">Concept: Actor</a> for more information.
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| </p>
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| <h4>
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| Use Case
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| </h4>
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| <p>
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| A model element representing&nbsp;each use case. Properties include the use case name and use case specification. See
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| <a class="elementLinkWithType" href="./../../../openup/workproducts/use_case-2.html"
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| guid="_0VGbUMlgEdmt3adZL5Dmdw">Artifact: Use Case</a> and <a class="elementLinkWithType"
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| href="./../../../openup/guidances/concepts/use_case-4.html" guid="_KudM0NcJEdqz_d2XWoVt6Q">Concept: Use Case</a> for
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| more information.
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| </p>
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| <h4>
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| Associations
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| </h4>
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| <p>
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| Associations are used to describe the relationships between actors and the use cases they participate in. This
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| relationship is commonly known as a “communicates-association”.
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| </p>
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| <h3>
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| Advanced model elements
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| </h3>
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| <p>
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| The use-case model may also contain the following advanced model elements.
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| </p>
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| <h4>
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| Subject
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| </h4>
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| <p>
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| A model element that represents the boundary of the system of interest.&nbsp;&nbsp;
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| </p>
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| <h4>
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| Use-Case Package
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| </h4>
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| <p>
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| A model element used to structure the use case model to simplify analysis, communications, navigation, and
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| planning.&nbsp; If there are many use cases or actors, you can use use-case packages to further structure the use-case
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| model in much the same manner you use folders or directories to structure the information on your hard-disk.
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| </p>
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| <p>
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| You can partition a use-case model into use-case packages for several reasons, including:
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| </p>
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| <ul>
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| <li>
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| To reflect the order, configuration, or delivery units in the finished system thus supporting iteration planning.
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| </li>
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| <li>
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| To support parallel development by dividing the problem into bite-sized pieces.
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| </li>
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| <li>
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| To simplify communication with different stakeholders by creating packages for containing use cases and actors
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| relevant to a particular stakeholder.
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| </li>
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| </ul>
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| <h4>
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| Generalizations
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| </h4>
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| <p>
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| A relationship&nbsp;between actors to support re-use of common properties.
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| </p>
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| <h4>
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| Dependencies
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| </h4>
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| <p>
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| A number of dependency types between use cases are defined in UML. In particular, &lt;&lt;extend&gt;&gt; and
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| &lt;&lt;include&gt;&gt;.
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| </p>
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| <p>
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| &lt;&lt;extend&gt;&gt; is used to include optional behavior from an extending use case in an extended use case.
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| </p>
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| <p>
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| &lt;&lt;include&gt;&gt; is used to include common behavior from an included use case into a base use case in order to
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| support re-use of common behavior.
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| </p>
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| <p>
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| The latter is the most widely used dependency and is useful for:
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| </p>
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| <ul>
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| <li>
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| Factoring out behavior from the base use case that is not necessary for the understanding of the primary purpose of
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| the use case to simplify communications.
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| </li>
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| <li>
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| Factoring out behavior that is in common for two or more use cases to maximize re-use, simplify maintenance and
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| ensure consistency.
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| </li>
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| </ul>
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| <h3>
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| Example Use-Case Diagram
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| </h3>
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| <p>
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| Figure 1 shows a use-case diagram from an Automated Teller Machine (ATM) use-case model.
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| </p>
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| <p>
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| &nbsp;<img height="410" alt="Figure 1: ATM Use-Case Diagram" src="./resources/atm_uc_diagram.GIF" width="565" />
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| </p>
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| <p>
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| Figure 1: ATM Use-Case Diagram
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| </p>
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| <p>
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| This diagram shows the subject (atm:ATM), four actors (Bank Customer, Bank, Cahier and Maintenance Person), five use
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| cases (Withdraw Cash, Transfer Funds, Deposit Funds, Refill Machine and Validate User), three &lt;&lt;includes&gt;&gt;
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| dependencies, and the associations between the performing actors and the use cases.
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| </p>
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| <p>
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| The use cases Withdraw Cash, Deposit Funds, and Transfer Funds all need to include how the customer is identified to
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| the system. This behavior can be extracted to a new inclusion use case called Validate User, which the three base use
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| cases &lt;&lt;include&gt;&gt;. The base use cases are independent of the method used for identification, and it is
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| therefore encapsulated in the inclusion use case. From the perspective of the base use cases, it does not matter
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| whether the method for identification is to read a magnetic bank card, or perform a retinal scan. They only depend on
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| the result of Validate Customer.
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| </p>
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| <p>
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| Note that Figure 1 is only a partial view of the use-case model. The complete use-case model also includes descriptions
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| of each actor, descriptions of each use case, and use-case specifications for each use case.&nbsp; For a more complete
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| example of this use case model see <a class="elementLinkWithType"
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| href="./../../../openup/guidances/examples/uc_model_evolve.html" guid="_t4QdAMNqEdu2IdAIaWZyAw">Example: Evolution of
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| the Use-Case Model</a>.<br />
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| </p></mainDescription> |
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