1. Requirements and Use Cases
Modelling
Class T04
Requirements and Use Cases
References:

2. UML and SysML
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3. UML – An overview…
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4. SysML – An overview…
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5. A Context Diagram (example for a HybridSUV system)
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6. Use Cases
Use cases describes an interaction between the system and other external entity (an actor).
The description must be provided from the point of view of the actor! Therefore it describes "who" can do or is affected by "what" with or from the system.
The use case technique is used to elicit functional requirements by relating them with usage/behavioral scenarios.
In a document requirements the use cases can be presented before the lists of requirements, as they can provide good glimpses…
Use cases are also useful to make the bridge between the requirements documenting and the modeling of the detailed systems’ behavior
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7. High level use cases
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8. High level use cases
Use Cases
Actors
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9. High level use cases
These actors might be the same object, but conceptually we must consider them independents
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10. Casos de Uso: Example of a template
Name
UC-8: Search
Summary
All occurrences of a search term are replaced with replacement text.
Rationale
While editing a document, many users find that there is text somewhere in the file being edited that needs to be replaced, but searching for it manually by looking through the entire document is time-consuming and ineffective. The search-and-replace function allows the user to find it automatically and replace it with specified text. Sometimes this term is repeated in many places and needs to be replaced. Other times, only the first occurrence should be replaced. The user may also wish to simply find the location of that text without replacing it.
Users
All users
Preconditions
A document is loaded and being edited.
Basic Course of Events
The user indicates that the software is to perform a search-and-replace in the document.
The software responds by requesting the search term and the replacement text.
The user inputs the search term and replacement text and indicates that all occurrences are to be replaced.
The software replaces all occurrences of the search term with the replacement text.
Alternative Paths
In step 3, the user indicates that only the first occurrence is to be replaced. In this case, the software finds the first occurrence of the search term in the document being edited and replaces it with the replacement text. The postcondition state is identical, except only the first occurrence is replaced, and the replacement text is highlighted.
In step 3, the user indicates that the software is only to search and not replace, and does not specify replacement text. In this case, the software highlights the first occurrence of the search term and the use case ends.
The user may decide to abort the search-and-replace operation at any time during steps 1, 2 or 3. In this case, the software returns to the precondition state.
Postconditions
All occurrences of the search term have been replaced with the replacement text.
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11. Driver’s use cases
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12. Driver’s use cases
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13. Driver’s use cases
Complex use cases can be detailed in other diagrams…
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14. SysML – An overview…
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15. Requirements and Stakeholders
A requirement specifies a capability or condition that must (or should) be satisfied.. A requirement may specify a function that a system must perform or a performance condition that a system must satisfy. Requirements are used to establish a contract between the customer (or other stakeholder) and those responsible for designing and implementing the system.
Stakeholders
Anybody involved in the system’s lifecycle (analysis, design, development, maintenance, …)
Anybody else who, directly or indirectly, may impose requirements for the system (business owner, user, …)
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16. Types of requirements Functional Requirements (FR)
The specification of a function of the system or its components.
It must refer a behaviour of the system!
Non-Functional Requirements (NFR)
It must refer how the system must behave.
Examples of non-functional requirements: Performance; Scalability; Availability; Reliability; Maintainability; Serviceability; Security; Regulatory; Manageability; Usability; Interoperability
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17. Requirements specification
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18. Requirements derivation
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19. Requirements in the Enterprise Architect…
VERY IMPORTANT:
Be aware that EA tool supports requirements diagrams as
formal SysML Requirements Diagrams
or as
informal requirements diagrams as extensions to UML
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20. Requirements containment
The containment (cross hair) relationship refers to the practice of decomposing a complex requirement into simpler, single requirements.
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21. Copy relationship
A Copy relationship is a dependency between a supplier requirement and a client requirement that specifies that the text of the client requirement is a read-only copy of the text of the supplier requirement. A Copy dependency created between two requirements maintains a master/slave relationship between the two elements for the purpose of requirements re-use in different contexts. When a Copy dependency exists between two requirements, the requirement text of the client requirement is a read-only copy of the requirement text of the requirement at the supplier end of the dependency.
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22. Callout relationship (notes)
A callout notation can be used to represent derive, satisfy, verify, refine, copy, and trace relationships…
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23. DeriveReqt relationship
A DeriveReqt relationship is a dependency between two requirements in which a client requirement can be derived from the supplier requirement.
For example, a system requirement may be derived from a business need, or lower-level requirements may be derived from a system requirement.
As with other dependencies, the arrow direction points from the derived (client) requirement to the (supplier) requirement from which it is derived.
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24. Verify relationship
A Verify relationship is a dependency between a requirement and a test case or other model element that can determine whether a system fulfills the requirement.
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25. Satisfy relationship
A Satisfy relationship is a dependency between a requirement and a model element that fulfills the requirement.
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26. Refine relationship
The refine requirement relationship can be used to describe how a model element or set of elements can be used to further refine a requirement. For example, a use case or activity diagram may be used to refine a text-based functional requirement. Alternatively, it may be used to show how a text-based requirement refines a model element. In this case, some elaborated text could be used to refine a less fine-grained model element
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27. Trace relationship
A generic trace requirement relationship provides a general-purpose relationship between a requirement and any other model element. The semantics of trace include no real constraints and therefore are quite weak. As a result, it is recommended that the trace relationship not be used in conjunction with the other requirements relationship...
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28. Relating requirements with other elements
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29. Use Cases
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30. Use cases and requirements
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31. Traceability in the Enterprise Architect tool
A fundamental technique in modelling to relate decisions with their origin or implications
Traceability in the Enterprise Architect tool
Traceability Diagrams
Relationship Matrix
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