IS 401 System Sequence Diagram

Question 1

system sequence diagram (SSD)

Answer 1

is used to describe this flow of information into and out of the automated system. Thus, an SSD documents the inputs and the outputs and identifies the interaction between actors and the system.

Question 2

An SSD is a type of interaction diagram.

Answer 2

.

Question 3

stick figure

Answer 3

actor - a person (or role) that interacts with the system

the emphasis in an SSD is on how the actor “interacts” with the system by entering input data and receiving output data.

Question 4

The box labeled :System is an object that represents

Answer 4

the entire automated system.

Question 5

object notation

Answer 5

In SSDs and all other interaction diagrams, analysts use object notation instead of class notation. In object notation, a box refers to an individual object, not the class of all similar objects. The notation is simply a rectangle with the name of the object underlined. The colon before the underlined class name is a frequently used but optional part of the object notation.
In an interaction diagram, the messages are sent and received by individual objects, not by a class. In an SSD, the only object included is one representing the entire system.

Question 6

Underneath the actor and :System are vertical dashed lines called lifelines

Answer 6

A lifeline, or object lifeline, is simply the extension of that object—either actor or object—during the use case.

Question 7

The arrows between the lifelines represent

Answer 7

the messages that are sent by the actor. Each arrow has an origin and a destination. The origin of the message is the actor or object that sends it, as indicated by the lifeline at the arrow’s tail.
Similarly, the destination actor or object of a message is indicated by the lifeline that is touched by the arrowhead. The purpose of lifelines is to indicate the sequence of the messages sent and received by the actor and object. The sequence of messages is read from top to bottom in the diagram.

Question 8

A message is labeled

Answer 8

to describe its purpose and any input data being sent. The message name should follow the verb-noun syntax to make the purpose clear. The syntax of the message label has several options
In a sequence diagram, a message is an action that is invoked on the destination object, much like a command

Question 9

A dashed arrow indicates

Answer 9

a response or an answer
Because it is a response, only the data that is sent on the response is noted
There is no message requesting a service—only the data being returned.

Question 10

Solid arrow

Answer 10

The syntax is simply the name of the message followed by the input parameters in parentheses.

Question 11

A note

Answer 11

can be added to any UML diagram to add explanations.

Question 12

loop frame

Answer 12

In a smaller rectangle at the top of the frame is the descriptive text to control the behavior of the messages within the larger rectangle. The condition loop for all items indicates that the messages in the box repeat many times or are associated with many instances.

Question 13

true/false condition

Answer 13

brackets

Question 14

The asterisk (*) preceding the true/false condition indicates

Answer 14

that the message repeats as long as the true/false condition evaluates to true.

EX: *[another item]

Question 15

Analysts use this abbreviated notation for several reasons

Answer 15

First, a message and the returned data can be shown in one step.
Second, the true/false condition is placed on the message itself

Question 16

Here is the complete notation for a message:

Answer 16

[true/false condition] return-value := message-name (parameter-list)

An asterisk (*) indicates repeating or looping of the message.
Brackets [ ] indicate a true/false condition. 
Message-name is the description of the requested service. It is omitted on dashed-line return messages, which only show the return data parameters.
Parameter-list (with parentheses on initiating messages and without parentheses on return messages) shows the data that are passed with the message.
Return-value on the same line as the message (requires :=) is used to describe data being returned from the destination object to the source object in response to the message.

Question 17

opt frame

Answer 17

is used when a message or a series of messages is optional or based on some true/false condition.

Question 18

alt frame

Answer 18

is used with if-then-else logic
The alt frame in this figure indicates that if an item is taxable, then add sales tax; otherwise, add a tax exemption code for a sales tax exemption.