Systems analysis and design exam 2 study guide (chapter 6)

When drawing a communication diagram, what guidelines should you follow?

1. Apply sequence diagram guidelines 1 - 4 in question 9. 2. Do not use communication diagrams to model process flow. 3. Use a sequence diagram instead of a communication diagram when sequencing is important.

When drawing a behavioral state machine, what guidelines should you follow?

1. Only create behavioral state machines for "complex" objects. 2. Draw the initial state in the top left corner of the diagram. 3. Draw the final state in the bottom right corner of the diagram. 4. Use simple, but descriptive, names for states. 5. Question "black hole" and "miracle" states. 6. Guard conditions should be mutually exclusive. 7. Transitions should be associated with messages and operations.

When drawing a sequence diagram, what guidelines should you follow?

1. Strive for left to right ordering of messages 2. If an actor and object represent the same idea, name them the same. 3. Place the initiator of the scenario on the left of diagram. 4. When there are multiple objects of the same type, be sure to name them. 5. Only show return values when not obvious. 6. Justify message names and return values near the arrowhead.

Describe the type of class that is best represented by a behavioral state machine. Give two examples of classes that would be good candidates for behavioral state machine.

A class that responds to multiple events and that has significant changes in state over time. Examples include: invoices and purchase orders; inventories

How are guard conditions shown on a behavioral state machine?

A guard condition is a Boolean expression that includes attribute values, which allows a transition to occur only if the condition is true. The Boolean expression is placed in brackets and located along the relevant transition.

Why is iteration important when creating a behavioral model?

As we develop, expand, and validate one model, we learn more about other aspects of the system, which helps us elaborate on allied models. As we learn about system behaviors, we come to understand more about the structures needed to support them. We need to update older models to reflect the new learning. In the process of that updating, we may learning more, create more questions, and need to update additional models until the entire set is more or less stable.

Identify the model(s) that contain each of the following components:

Behavioral State Machine State, final state, initial state, event, transition, guard condition Collaboration Diagram Actor, object, association, message Sequence Diagram Actor, object, lifeline, focus of control, message, object destruction Class Diagram Class, attributes, operations, associations, multiplicity CRC Card Class name, ID, type, description, associations, responsibilities, collaborators, attributes, relationships, aggregation, generalization, extends associations Use Case Use case name, ID, importance, actor, stakeholders, trigger and relationships

How is behavioral modeling related to structural modeling?

Behavioral models describe the internal dynamic aspects of an information system that supports the business processes in an organization. Behavioral modeling describes that things that happen and changes that occur during use of a system whereas structural modeling describes the essentially permanent elements of the system.

What is CRUD analysis and what is it used for?

CRUD analysis is a useful technique for identifying potential collaborations. CRUD analysis uses a CRUD matrix, in which each interaction among objects is labeled with a letter for the type of interaction: C for create, R for read or reference, U for update, and D for delete. In an object-oriented approach, a class/actor-by-class/actor matrix is used.

How do you show the sequence of messages on a communication diagram?

Each message is given a number that corresponds with the order in which the message is transmitted.

How does a use case relate to a sequence diagram? A communication diagram?

In UML, the sequence and communication diagrams are used to show the underlying details of business processes portrayed by the use case model.

What kinds of events can lead to state transitions on a behavioral state machine?

In the parlance of behavioral state machines, every event leads to a state transition. This is because events are defined as anything that changes a value which in turn describes the state of the behavioral state machine. In other words, transitions occur only as the result of an event. Specific types of events are as follows. a) Data value change: a change in one of the data values that collectively describe the state of the object. For example, a patient transitions from "new" to "existing" after the first visit. b) Boolean condition: a Boolean test that is applied at a certain point. For instance, after a patient transitions to "existing" we may ask the question "is the patient insured?" which would lead to state changes based on billing policies. c) Time lapse: after a certain amount of time in a given state, the object may spontaneously change to a different state. For instance, a patient that is in state "inactive" (perhaps because he/she has no future appointments), may be removed from the system after 5 years.

Are states always depicted using rounded rectangles on a behavioral state machine? Explain.

Most of the time they are. The exceptions are the initial state and the final state. These are shown with a filled in circle for initial state and a "bullseye" circle for the final state.

Do lifelines always continue down the entire page of a sequence diagram? Explain.

No. When the object continues to exist for the entire sequence of events, then it will continue down to the bottom of the diagram. Otherwise, an "x" shows where it ends.

How do you show that a temporary object is to go out of existence on a sequence diagram?

Place an "x" at the bottom of its lifeline to show that a temporary object is to go out of existence on a sequence diagram. A dotted line runs vertically below each actor and object to denote the lifeline of the actors/objects over time. Sometimes an object creates a temporary object, and in this case an X is placed at the end of the lifeline at the point the object is destroyed. For example, think about a shopping cart object for a Web commerce application. The shopping cart is used for temporarily capturing line items for an order, but once the order is confirmed, the shopping cart is no longer needed. In this case, an X would be located at the point at which the shopping cart object is destroyed.

Describe the main building blocks for the communication diagram and how they are represented on the model.

The main elements of the communication diagram are the actor, object, association, and message. The actor is the person or system that initiates and derives benefit from the system. Objects participate in the sequence of activities by receiving or sending messages. An association shows a link between actors and/or objects by which messages are conveyed. A message shows that information is being conveyed from one object to another. The actor is represented by a stick figure; the object by a rectangle with the object and class names inside; the lifeline by a vertical dotted line; an association is represented by a straight line; and the message by an arrow directed line with the name of the message nearby.

What are the main building blocks for the sequence diagram? How they are represented on the model?

The main elements of the sequence diagram are the actor, object, lifeline, focus of control, message, and object destruction. The actor is the person or system that initiates and derives benefit from the system. Objects participate in the sequence of activities by receiving or sending messages. A lifeline denotes the life of an object from creation to when it is no longer needed. A focus of control shows which objects are sending and receiving messages at a particular time. A message shows that information is being conveyed from one object to another. Object destruction shows when the need for an object is finished and the object is removed from existence. The actor is represented by a stick figure; the object by a rectangle with the object and class names inside; the lifeline by a vertical dotted line; the focus of control by a thin vertical rectangle; the message by an arrow directed line with the name of the message above. The object destruction is shown by an "x" at the end of an object's lifeline.

How do you show the direction of a message on a communication diagram?

You show the direction of the message by adding an arrowhead to the side of the message line to which the message is directed.

What are the steps in building a behavioral state machine?

a) Determine the context of the behavioral state machine, usually a class. b) Identify the various states that an object will have over its lifetime including the boundaries of initial and final states. c) Determine the sequence through the states that the object can pass over its lifetime. d) Identify events, actions, and guard conditions associated with the transition between states. e) Validate the behavioral state machine that it is possible to reach the final state and that it is possible to leave each state, except the final state.

Describe the steps used to create a sequence diagram.

a) The context of the sequence diagram must be determined. Usually, this is a scenario from a use case. b) The objects to be used in the sequence being modeled are identified. c) The lifeline for each object is set. d) Messages are added to the diagram. e) The focus of control on each object's lifeline is drawn in. f) The sequence diagram is validated to make sure that all steps in the process have been accounted for.

Describe the steps used to create a communication diagram

a) The context of the sequence diagram must be determined. Usually, this is a scenario from a use case. b) The objects/actors and associations that collaborate need to be identified. One method for doing this is using the CRUD matrix to identify all relevant combinations. c) The objects/actors are laid out with their associations displayed. d) Message names and directions are added. e) The collaboration diagram is validated to make sure that all associations in the process have been accounted for.

Contrast the following sets of terms:

a) state; behavior b) class; object c) action; activity Objects have behaviors that are described by operations. The state of an object at a given point in time is the collection of data available. The purpose of behavior is largely to transition the object from one state to a new state. The class is a template that generates objects. Objects become available to be instantiated with data that pertain to a particular instance of the class/object. An action is an atomic, non-decomposable process that cannot be interrupted. They are associated with transitions. In contrast, the activity is non-atomic and decomposable process that is in essence comprised of actions. These are associated with states.