System and Sequence Diagrams

Part 1 Analysis

Interface - is the top two layers

Boundary - shows the information to the user

Control layer - takes user input, and control sequence of execution

Entity - data model of the real world entities

Database layer - contains the tables and the mapping for object oriented artifacts

Database - the storage

Goal

To create a conceptual model of the system and its functionality

Not concerned with: interface, software and hardware architecture, concurrency

Types of diagram

What is an object

Object is an individual item with a well defied roll in a problem

How to draw classes and objects

Part 2 Use Case descriptions

Use case description - text based description

Each use case represents a sequence of events, the diagram should show all scenarios

What a distinction needs:

  1. The name
  1. Quick description
  1. Actors involved
  1. Preconditions
  1. Details description of the flow of events, including outliers
  1. Post conditions, what will the state be at the end

Part 3 Sequence Diagrams

Interaction diagrams - shows how objects interact via messages, sequence diagrams are a type of interaction diagram

Message is an interaction between two objects, normally involves a verb “actor inserts a card into the machine”

Note: Objects do not have names in the diagram

Reflexive Message

Create and Remove Objects

Combined Fragments

What happens when you have alternative flows

Alt else - if else

Opt - if without the else

Break - break out of a fragment

Loop - loop

Alt else

Multiple conditions

Loop

Object loop

Option

Break