Normal use cases description

A normal use case includes a Title, Description, System Under Design field, Scope field, Level field, a Primary Actor field, a Participants field, a Goal field, a list of Following Use Cases field, a Precondition, an Invariant, a Success Postcondition, a sequence of Steps, a set of Any Extensions, and a set of Extension Points. The description of these elements is as follow.

• Title: a label that uniquely identifies the use case within the use case model.
• Description: a free form text that summarizes the use case.
• System Under Design specifies what is the system in the use case. The system is the entity that react to stimuli from external actors.
• Scope: specifies what system is being considered black box under design (e.g. whole business, system, sub-system, function).

  The different possible values for scope are defined in property file traits.properties.

• Level: is the use case level of detail.

  The different possible values for scope are defined in property file traits.properties.

• Primary Actor: the actor that initiates the use case.
• Participants: other actors participating in the use case.
• Goal: a statement of the primary actor expectation at the successful completion of the use case.
• Follows Use Cases: a list of normal use cases that the use case directly follow.

  A follow list expression reflects how the listed use cases are synchronized in relation to the described use case. Two operators are used. Operator AND expresses synchronization (synchronized follow list), while operator OR expresses asynchronism (unsynchronized follow list).

  Given use cases $uc_{0}$, $uc_{1}$, $uc_{2}$, $\cdots$, $uc_{n}$, the following interpretation is given.

  • If the follow list of $uc_{0}$ is specified as `` '', all of $uc_{1}$, $uc_{2}$, $\cdots$, $uc_{n}$ must reach a point from which use case $uc_{0}$ is enabled before use case $uc_{0}$ (synchronism).
  • If the follow list of $uc_{0}$ is specified as `` '', use case $uc_{0}$ may be executed as soon as any of use cases $uc_{1}$, $\cdots$, $uc_{n}$ reaches a point from which use case $uc_{0}$ is enabled (asynchronism).
  When a use case $uc_{i}$ refers to a use case $uc_{j}$ in its follow list, use case $uc_{j}$ must include an enabling directive referring to use case $uc_{i}$.

• Invariant: a condition that must hold through the use case.
• Precondition: a condition that must hold before an instance of the use case can be executed.
• Success Postcondition: a condition that must be true at the end of a 'successful' execution of an instance of the use case.
• Steps: a sequence of repeat blocks and steps.

  A repeat block is a sequence of steps that are supposed to repeat based on time and/or condition.

  Each step references a use case step operation.

  A use case step operation may be a concept operation instance, a branching statement or a use case sequencing statement.

  A step may also include a set of step extensions and an alternative postcondition. Each step extension defines an alternative behavior (secondary scenario) following the step. Alternative postconditions are conditions that must hold at the end of the secondary scenario defined by an step extension.

• Any Extensions: a set of step extensions that applies to all the steps in the use case.
• Extension Points: a set of locations in the use case steps where additional behaviors defined in extension use cases might be inserted.

A use case description can be seen as a two parts description with:

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a static part that includes the use case Title, Description, System Under Design, Scope, Level, Primary Actor, a Participants, Goal, a list of Following Use Cases, Precondition, Invariant, and Success Postcondition fields,

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a dynamic or procedural part that consists of the use case Steps.