Chapter 5: Extending the Requirements Model

Jo Hart
Flashcards by Jo Hart, updated more than 1 year ago
Jo Hart
Created by Jo Hart about 6 years ago


Extending the Requirements Model

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Question Answer
use case – description a textual model that lists and describes the processing details for a use case
scenarios or use case instances – unique sets of internal activities within use cases
precondition – a condition that must be true before a use case begins
postcondition – what must be true upon the successful completion of a use case
system sequence diagram (SSD) – a diagram showing the sequence of messages between an external actor and the system during a use case or scenario
interaction diagram – either a communication diagram or a sequence diagram that shows the interactions between objects
lifeline or object lifeline – the vertical line under an object on a sequence diagram to show the passage of time for the object
loop frame – notation on a sequence diagram showing repeating messages
true/false condition – part of a message between objects that is evaluated prior to transmission to determine whether the message can be sent
opt frame – notation on a sequence diagram showing optional messages
alt frame – notation on a sequence diagram showing if-then-else logic
state – a condition during an object’s life when it satisfies some criterion, performs some action, or waits for an event
transition – the movement of an object from one state to another state
state machine diagram – a diagram showing the life of an object in states and transitions
pseudostate – the starting point of a state machine diagram, indicated by a black dot
destination state – for a particular transition, the state to which an object moves after the completion of a transition
origin state – for a particular transition, the original state of an object from which the transition occurs
action-expression – a description of the activities performed as part of a transition
guard-condition – a true/false test to see whether a transition can fire
concurrency or concurrent state – the condition of being in more than one state at a time
path – a sequential set of connected states and transitions
composite state – a state containing other states and transitions (that is, a path)
What are the models that describe use cases in more detail? Fully developed use case description, activity diagrams, and system sequence diagrams.
What two UML diagrams are used to model domain classes? Problem domain class diagram and state machine diagram.
Which part of a use case description can also be modeled by using an activity diagram? The “flow of activities” section.
Explain the difference between a use case and a scenario. Give a specific example of a use case with a few possible scenarios. A use case is the entire function or user goal or event. A scenario is one specific version or instance of that use case. From RMO we have Create customer account as a use case. But we might have Create online Customer account and Create instore customer account and even Create phone customer account as different scenarios.
List the parts or compartments of a fully developed use case description.  Use case name  Scenario  Triggering event  Brief description  Actors  Related use cases  Stakeholders  Preconditions  Postconditions  Flow of activities  Exception conditions
Compare/contrast precondition and postcondition. A precondition describes the “states” of data and the system that must exist before the use case can begin. For example to add an item to a shopping cart, the item must exist in the database. A postcondition describes the states of data and the system that must exist after the use case completes. For example after Create a customer account use case, a customer account object (record) must exist.
Compare/contrast postcondition and exception condition. A post condition, as explained about describes states of the data and the system. An exception condition describes some non-normal situation in the processing, i.e. in the flow of activities, that must be handled in some way..
Compare/contrast business process and flow of activities for a use case. Explain how an activity diagram can be used to model both. A business process is larger than a use case. A business process might include various manual business procedures both before and after the “business event” that causes the use case to occur. However, an activity diagram is a powerful model to describe all types of sequences of tasks and activities. The various swimlanes can represent various users or user groups as well as system activities.
What is the purpose of an SSD? What symbols are used in an SSD? An SSD (system sequence diagram) is used to describe the messages that flow into and out of a system, i.e. between the system and the use case user. The symbols include:  Stick figure for the actor  Box with object name for the system object  Vertical dashed lines for object lifelines  Horizontal arrows for messages  Horizontal dashed arrows for return data  Comment box for comments
What are the steps required to develop an SSD? 1. Identify the input messages (from the activity diagram) 2. Describe the input message using the SSD message syntax 3. Add message conditions such as looping or true/false conditions 4. Add all output message data
Write a complete SSD message from the actor to the system, with the actor asking the system to begin the process for updating information about a specific product. updateProductInformation (productID, updateInformation)
What is the name of the sequence diagram symbol used to represent the extension of an object throughout the duration of a use case? Lifeline or object lifeline
What are the two ways to show a returned value on a sequence diagram? Either with a return value on the left hand side of the equal (:=) sign, or with a return message shown by a dashed line and labeled with the return data.
What are two ways to show repetition on a sequence diagram? Either with an asterisk on the message label or a loop frame around the message(s).
What are the three types of frames used on a sequence diagram? Loop frame – repeat or loop the contents of the frame Opt frame – send or do not send the message based on true/false condition Alt frame – if-else alternative flows based on condition
What is the symbol for a true/false condition on a sequence diagram? A true/false condition is shown in brackets [ ]
What are the parameters of a message? The parameters represent the input data, i.e. the data that is being passed to the destination object.
What is an object state? An object state is the state of being of an object, and is usually measured by a set of values. It is comparable to a status condition.
What is a state transition? A state transition is the movement of an object from one state to another state.
When considering requirements, states and state transitions are important for understanding which other diagram? States and Transitions are part of the state machine diagram for an object class. Therefore, they help to understand the objects in the class diagram.
What UML diagram is used to show the states and transitions for an object? States and Transitions are part of the state machine diagram, which describes the activity of the objects in an object class.
List the elements that make up a transition description. Which elements are optional? Transition-name (parameters, ... ) [guard-condition] / action-expression Any of the three elements may be empty, i.e. are optional.
What is a composite state? What is it used for? A composite state is a high-level state in that it may have other states and transitions inside of it. It is used to represent concurrent states. For example, a printer may be in the “on” state, which is a composite state, and it may be “idle” which is an internal state within “on.”
What is meant by the term path? A path is a sequence of states and transitions. It may be a complete path to describe an entire origin to destination path, or it may be a “snippet” of a path and only contain a few states and transitions.
What is the purpose of a guard-condition? A guard-condition determines whether or not a transition can fire. Usually first the trigger fires to notify the transition that it should execute, but before it begins execution, it tests to see if the guard-condition is true.
Identify the models explained in this chapter and their relationship to one another. The two main models for requirements are the Use case model,which identifies the use cases or the “processes,” and the Domain model class diagram, which identifies the information or data for the system. The Use case diagram is supported by Use Case Descriptions, Activity diagrams, and System Sequence diagrams. The Domain model class diagram is supported by State machine diagrams.
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