OSM for a digital watch

 This description uses OSM version 2 (for full paper, see Blandford and Green 1998)

 date: Feb 98

a) The shared description

entities:

entity

type

add by

delete by

attribute

set by

change by

notes

GMT/'real' time
user private
-
-
current time
-
-
externally defined
time shown
shared/domain
-
-
hours shown
-
change hours

 

minutes shown

change minutes

seconds shown
-
change seconds

 

energy
device private
-
-
amount
-
decreases as watch runs; increase by changing battery

display type
shared/device
-
-
time/alarm
defaults to time
change dislay mode

alarm time
shared/domain
-
-
hours, minutes, secomds
-
change alarm time

relationships:

domain constraint:

time shown should be same as GMT

device constraint:

watch can only work if it has enough energy; only a finite amount of energy can be stored

 b) Adding domain knowledge

How users use the device: Digital watches are used heavily in the following ways:

  1. telling the time of day
  2. elapsed time (how long has this process been going on?)
  3. time-remaining (how much longer will it go on?)
  4. time-of-completion (what will the time be when this process has continued for X minutes?)
  5. alarm clock (sound an alarm when time of day = X)
  6. countdown (sound an alarm when elapsed time = X)
  7. current time in other time zones

We have chosen to model a watch with no countdown alarm, to keep the example simple.

Domain concepts and relationships: Each of the above introduces a further domain concept.

Context of usage, and related tools or devices: Digital watches are used in conjunction with analogue clocks and watches and time-of-day needs to be translated from one to the other.

 

c) Expanding the device description

conceptual action
device actions
device object
persistence
disguised?
notes
Change time hours
any or all buttons may have to be pressed (see diagram)
buttons 1, 2, 3
high
yes (because overloaded)

Change time minutes
ditto
ditto
high
ditto

Change time second
ditto
ditto
high
ditto

Change alarm time
ditto
ditto
high
ditto

Change battery
open battery compartment (not modelled), replace battery, close compartment
compartment, old battery, new battery
high
no

 

d) Misfits etc

 

Illustration

diagram of 3-button digital watch

transition diagram for 3-button digital watch

return to OSM index

 


last updated: Feb 99