Page 351 -

322 PART THREE CONVENTIONAL METHODS FOR SOFTWARE ENGINEERING

FIGURE 12.20
Control
Context-level Control User commands Display panel
DFD for panel and data information display
SafeHome
Alarm
type
SafeHome Alarm
software

Sensor Telephone Telephone
Sensors status number tones line

commands, all miscellaneous interactions, and all data that are entered to qualify or
expand a command.
The level 0 DFD is now expanded into a level 1 model. But how do we proceed?
A simple, yet effective approach is to perform a "grammatical parse" on the processing
narrative that describes the context level bubble. That is, we isolate all nouns (and
noun phrases) and verbs (and verb phrases) in the SafeHome narrative originally pre-
sented in Chapter 11. To illustrate, we again reproduce the processing narrative under-
lining the first occurrence of all nouns and italicizing the first occurrence of all verbs. 3
SafeHome software enables the homeowner to configure the security system when it is
installed, monitors all sensors connected to the security system, and interacts with the home-
owner through a keypad and function keys contained in the SafeHome control panel shown
The grammatical parse in Figure 11.2.
is not foolproof, but it
will provide you with During installation, the SafeHome control panel is used to "program" and configure the
an excellent jump start system. Each sensor is assigned a number and type, a master password is programmed for
if you’re struggling to arming and disarming the system, and telephone number(s) are input for dialing when a
define data objects sensor event occurs.
and transforms. When a sensor event is recognized, the software invokes an audible alarm attached to
the system. After a delay time that is specified by the homeowner during system configura-
tion activities, the software dials a telephone number of a monitoring service, provides infor-
mation about the location, reporting the nature of the event that has been detected. The
telephone number will be redialed every 20 seconds until telephone connection is obtained.
All interaction with SafeHome is managed by a user-interaction subsystem that reads
input provided through the keypad and function keys, displays prompting messages on the
LCD display, displays system status information on the LCD display. Keyboard interaction
takes the following form . . .

Referring to the "grammatical parse," a pattern begins to emerge. All verbs are
SafeHome processes; that is, they may ultimately be represented as bubbles in a sub-

3 It should be noted that nouns and verbs that are synonyms or have no direct bearing on the mod-
eling process are omitted.