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104 lines
3.1 KiB
Markdown
104 lines
3.1 KiB
Markdown
---
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title: Use case diagrams
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---
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# Use case diagrams
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- specifies the participants (actors) and the relationships between them
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- high level view of what a system does (not how) and who uses it
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- represent users perspective of a system
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- used mainly in requirements specification and early system dev
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- effectively a todo list
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## 1 pros
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+ informal,flexible, easy to construct
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+ easily understood
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+ improve communication between users and developers
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+ can be used to confirm requirements
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+ provide overview
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+ link analysis to design
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+ can be used to inform subsequent dev tasks
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+ derive test cases
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+ prioritise imlementation tasks
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+ help clarify new feature requests or bug reports
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## 2 Notation
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### 2.1 Actor
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- roles that people have when interacting with the system
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- external systems or hardware that are essential to system operation
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### 2.2 Use case
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- discrete unit of system functionality
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- activity from perpective of an actor
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- can be abstract or focused
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- say nothing about flow or behaviour
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- map to ⇒ menu items, forms, reports, etc
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### 2.3 Association
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- relationship (interaction) between actor and use casel
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- actor can be associated with more than one use case
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- use case can be associated with more than one actor
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- 
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### 2.4 Specialisation/generalisation
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- actors and use cases can be orgainsed into special/general hierachies
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- acotrs can be specialisations of another actor
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- same for use cases
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- mutually exclusive
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- similar to inheritance
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### 2.5 Dependency
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- occur between use cases
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- one case extends the behaviour of another
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- one case includes the behabiour of another
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- one case requires the behaviour of another
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- read in direction of arrow
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- indicate opportunities for reuse of functionality
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#### 2.5.1 Extends dependency
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- use cases can have optional, subordinate tasks
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- useful with specialised actors
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#### 2.5.2 Includes dependency
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- use cases that have mandatory, subordinate tasks
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- does not indicate sequence, only that they must happen
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#### 2.5.3 Requires dependency
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- mandatory, _independent_ tasks, that must be completed first
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- forces sequence
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- use sparingly
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## 3 development of use case diagrams
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organise related use case diagrms itno use case model
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- have have multiple levels of detail
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- group related diagrams into packages
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### 3.1 example methods
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- user goal technique ⇒ simple
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- event decompositition technique ⇒ more comprehensive
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### 3.2 top down
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identify actors ⇒ identify use cases ⇒ detail use cases
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- who will enter and/or recience information
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- what other systems will interact with the system
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- prioritise use cases
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- further develop use case, starting with highest priority
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- structure overall use case model
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> **avoid specifying the sequence**
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### 3.3 bottom up
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create scenario ⇒ generalise scenario ⇒ organise use case model
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## 4 Examples
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