Software Architecture Text Browser

Summary

• Problem
• Components
• Use Cases
• Analyisis Model
  • Exercise
• Operation
• Attributes
  • FileManager
• Relationships

Problem

Imagine you are building a text browser.

Components

What components would you need from a GUI library?

• Window
• Scrollbar

We also need a component to supply the text

• File Manager
  • Provide a module that can retrieve a limited length, consecutive subsequence of the file’s lines

ViewPort

• Need to be able to display textual content graphically
• Displays an integer number of lines
  • [0, 100]
• Can be resized
• All text is same font and point size.

ScrollBar

• Need to give user some way to access different parts of the file
• “Handle” sits in “tray”

Use Cases

Imagine how the user will use the intended solution

• Viewing Text
• Scrolling
• Resizing ViewPort

Analyisis Model

We will be using UML

• Rectangles for class/components
  • Divided vertically into 3 components
    1. Component Name
    2. Attributes
    3. Operations
• Lines between components denote relationships

Exercise

Create a diagram with classes for the three components we’ve identified

Apparently I was only supposed to fill it in with names and not like attributes and operations, but whatever I’m leaving it

Operation

Operations comprise those actions that the user can undertake to interact with the application.

• Moving Handle
• Resizing ViewPort

Can provide parameters and return types

Attributes

Attributes are things entities own/have

Percepts are attributes that the user can see

• Handle’s Position
• Size of ViewPort
• Text
• Size of Handle

FileManager

Not visible to the user

Supplies contents of the file

TextBrowser interacts with the file system through operating system

Document is a percept that is supplied by the operating system actor

Relationships

3 types

• Associations
• Aggregations
• Generalizations

context LinesVisible inv:
  ViewPort : viewContents->size() = ViewPort : height.min(FileManager : document->size())

func LinesVisible(vp ViewPort, fm FileManager) {
  vp.viewContents.size = Min(vp.height, fm.document.size)
}

context displays inv:
  let topLineNumber = Scrollbar : handlePosition *
    FileManager : document->size()
  in ViewPort : viewContents = FileManager :
    document->subsequence(topLineNumber, topLineNumber + ViewPort :
    viewContents->size() -1)

context scalesHandle inv:
  Scrollbar : handleSize = ViewPort : viewContents->size() / FileManager : document->size()