S

Chapter 5 System Modeling

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Context Model

Shows context (environment) of proposed system Other software People

Roadmap of major areas to consider

Other software systems Supplying data Using Data Sharing data Offering services User interface

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Context

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Process UML Activity Diagram

Show activities of a system

Symbology Filled circle – start of a process Rounded boxes – activities Arrows - flow Bars –

Full completion of predecessors needed successors occur in parallel

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Process – UML Activity Diag.

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Use Case Modeling

Each use case is a discrete task

Actors (stick figures) People Programs

Activity

Tabular description

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Use Case

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Use Case - textual

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MHC-PMS: Transfer data

Actors Medical receptionist, patient records system (PRS)

Description A receptionist may transfer data from the MHC-PMS to a general patient record database that is maintained by a health authority. The information transferred may either be updated personal information (address, phone number, etc.) or a summary of the patient’s diagnosis and treatment.

Data Patient’s personal information, treatment summary

Stimulus User command issued by medical receptionist

Response Confirmation that PRS has been updated

Comments The receptionist must have appropriate security permissions to access the patient information and the PRS.

Use - Case

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Sequence Diagrams

Actors, objects in boxes at top

Dotted line denotes their timeline

Solid box denotes their activity

Arrows show interaction between activities

Time flow is top to bottom

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Sequence Diagam

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Sequence Diagram

Sequence Diagrams

Web server access

Three tier model

FTP protocol

DHCP - Broadcast, Offer, Request, Acceptance

Web access/DNS

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Activity

Home security system Window, door sensors Central security system Phone confirmation Dispatch Security officer

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Class Diagrams

Define objects and object relationships

Box refers to a class

Line designates a relationship

Numbers identify quantity 1 – single * many

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Class Diagrams

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Class Detail

Name at top

Attributes next

Methods at bottom

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Class Detail

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Generalization hierarchy

Class hierarchy

Root represents base class, most common definition

Branches add attributes, operations

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Class Hierarchy

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Class Hierarchy - detailed

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Example

Real Estate Property Residential Commercial Land

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Data Driven Modeling

Processes are driven by data that arrives

UML Activity Diagram

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Data Driven Modeling

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Event Driven Modeling

Models behavior in response to events

Especially in real-time and embedded control systems

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State Diagrams

Model event driven process

Notation Circles

indicate states May indicate action

Arcs indicate event trigger may indicate output

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State Diagram Example

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States

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State Description

Waiting The oven is waiting for input. The display shows the current time.

Half power The oven power is set to 300 watts. The display shows ‘Half power’.

Full power The oven power is set to 600 watts. The display shows ‘Full power’.

Set time The cooking time is set to the user’s input value. The display shows the cooking time selected and is updated as the time is set.

Disabled Oven operation is disabled for safety. Interior oven light is on. Display shows ‘Not ready’.

Enabled Oven operation is enabled. Interior oven light is off. Display shows ‘Ready to cook’.

Operation Oven in operation. Interior oven light is on. Display shows the timer countdown. On completion of cooking, the buzzer is sounded for five seconds. Oven light is on. Display shows ‘Cooking complete’ while buzzer is sounding.

Events

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Stimulus Description

Half power The user has pressed the half-power button.

Full power The user has pressed the full-power button.

Timer The user has pressed one of the timer buttons.

Number The user has pressed a numeric key.

Door open The oven door switch is not closed.

Door closed The oven door switch is closed.

Start The user has pressed the Start button.

Cancel The user has pressed the Cancel button.

State Diagram

Graph structure

Can be characterized in tables – row contain State, trigger, new state

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State Diagrams - Examples

Fax decoding Data driven

Printer console Driven by buttons, internal sensors

Power Plant Control System

Stopwatch Stop, start Lap time

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Example

Alarm clock Three buttons Set time Set alarms Enable/disable alarm Change display – clock or alarm time Power Failure

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Model Driven Engineering

Developer defines model

Implementation is automatically generated

Not in widespread use

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