SWE202: System Behavior and Sequence Diagrams

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Questions and Answers

What is a key difference between a system sequence diagram and a standard sequence diagram?

The level of abstraction

The focus on specific use cases (correct)

The inclusion of external actors

The level of complexity

What does a system sequence diagram illustrate?

The use cases of the system

The internal workings of the system

The interactions between systems

Input and output events related to the systems under discussion (correct)

What is the purpose of a system sequence diagram according to the UML?

To model the system as a black box (correct)

To represent the user's interaction with the system

To illustrate the use cases of the system

To show the progression of events over time

What is a system sequence diagram an example of?

A type of sequence diagram in UML Signup and view all the answers

What is a characteristic of a system sequence diagram?

It presents sequences for specific use cases Signup and view all the answers

What is a system sequence diagram part of?

The use case model Signup and view all the answers

What does an object in a system sequence diagram represent?

A class or object in UML Signup and view all the answers

What do actors in a system represent?

Entities that interact with the system from outside Signup and view all the answers

What is the purpose of a system sequence diagram in the context of system behavior?

To describe what a system does Signup and view all the answers

What is the purpose of an operation contract?

To define system behavior in terms of state changes Signup and view all the answers

What is a key concept in system behavior?

Description of what a system does Signup and view all the answers

What is represented by a lifeline in an SSD?

A sequence of events Signup and view all the answers

How is a system modeled in a system sequence diagram?

As a black box Signup and view all the answers

What are pre-conditions in an operation contract?

Conditions that must hold true before operation execution Signup and view all the answers

What is the focus of an SSD?

Events that cross the system boundary Signup and view all the answers

What do post-conditions in an operation contract describe?

The state of the system after operation execution Signup and view all the answers

What is the main purpose of treating a system as a black box?

To emphasize events that cross the system boundary Signup and view all the answers

What do operation contracts describe in terms of?

State changes to objects in the domain model Signup and view all the answers

What is the relationship between an operation contract and a use case?

The operation contract occurs in a use case Signup and view all the answers

What is the purpose of an SSD?

To represent the system as a black box Signup and view all the answers

Study Notes

System Behavior

System behavior describes what a system does, without explaining how it does it.
A system sequence diagram (SSD) is a fast and easily created artifact that illustrates input and output events related to the systems under discussion.

System Sequence Diagrams (SSDs)

A SSD is a picture that shows, for a particular scenario of a use case, the events that external actors generate, their order, and inter-system events.
SSDs are a type of sequence diagram in UML, following the Unified Modeling Language style and notation.
SSDs show sequences for specific use cases, unlike standard sequence diagrams that show progression of events over time.

SSD vs. Sequence and Use Case Diagrams

Standard sequence diagrams show progression of events over time.
Use case diagrams represent a user's interaction with the system.
SSDs are part of the Use-Case Model, visualizing interactions implied in the use cases.

SSD Notations

Objects are represented by a box shape with an underlined title, modeling the system as a black box.
Actors are represented by stick figures, showing entities that interact with the system.
Events are represented by dashed lines (lifelines), showing system events generated by actors.

SSD Example

SSD treats all systems as a black box, emphasizing events that cross the system boundary from actors to systems.

Operation Contracts

Contracts for operations help define system behavior, describing the outcome of executing a system operation in terms of state changes to domain objects.
Contracts describe detailed system behavior in terms of state changes to objects in the Domain Model, after a system operation has executed.

Operation Contracts Components

Pre-conditions are conditions that the state of the system must satisfy before the execution of the operation.
Post-conditions are conditions that the system state has to satisfy after the execution of the operation.

Operation Contracts Schema

Operation: name of operation (parameters)
Cross Reference: the Use Cases in which the OC occurs
Preconditions: notable assumptions about the state of the system or objects in DM before execution
Postconditions: state of objects in DM after execution of operation

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Description

This quiz covers system behavior, sequence diagrams, and operation contracts in software construction. It is based on the lecture notes of Oluwaseun Priscilla Olawale (MSc.)