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:

telling the time of day
elapsed time (how long has this process been going on?)
time-remaining (how much longer will it go on?)
time-of-completion (what will the time be when this process has continued for X minutes?)
alarm clock (sound an alarm when time of day = X)
countdown (sound an alarm when elapsed time = X)
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

This device is very heavily moded.
Learning the transitions between modes is not trivial; there is no obvious way to reach the desired state 'alarm set for time T'. Informal observation suggests that this is the major usability problem.

Illustration

diagram of 3-button digital watch

transition diagram for 3-button digital watch

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last updated: Feb 99