2 RELATED WORK
A variable- (also changeable-, electronic-, or
dynamic-) message sign, often abbreviated VMS,
CMS, or DMS, and in the UK known as a matrix sign,
is an electronic traffic sign often used on roadways to
give travelers information about special events. Such
signs warn of traffic congestion, accidents, incidents,
roadwork zones, or speed limits on a specific highway
segment. In urban areas, VMS are used within
parking guidance and information systems to guide
drivers to available car parking spaces. They may also
ask vehicles to take alternative routes, limit travel
speed, warn of duration and location of the incidents
or just inform of the traffic conditions. A complete
message on a panel generally includes a problem
statement indicating incident, roadwork, stalled
vehicle etc.; a location statement indicating where the
incident is located; an effect statement indicating lane
closure, delay, etc. and an action statement giving
suggestion what to do traffic conditions ahead. These
signs are also used for AMBER Alert and Silver Alert
messages. In some places, VMSs are set up with
permanent, semi-static displays indicating predicted
travel times to important traffic destinations such as
major cities or interchanges along the route of a
highway. The information comes from a variety of
traffic monitoring and surveillance systems. It is
expected that by providing real-time information on
special events on the oncoming road, VMS can
improve vehicles' route selection, reduce travel time,
mitigate the severity and duration of incidents and
improve the performance of the transportation
network (Operations office of travel management,
1999).
3 THE VISUALIZATION TOOL
FOR THE VMS EMULATOR
The VMS emulator has the following functions; 1)
automatic variable text message generator system; 2)
real-time scheduling policy; 3) communication
method from server to client vice versa. To be
effective, a VMS must communicate a meaningful
message that can be read and understood by motorists
within a very short time period. And message design
involves recognition of the basic principles for the
following: 1) Message content refers to specific
information displayed on a VMS. 2) Message length
refers to rather the number of words or the number of
characters and spaces in a VMS message. 3) Message
load refers to the amount of information in the total
message, usually expressed in terms of units of
information. 4) Unit of informational refers to the
answer to a question a motorist might ask. 5) Message
format refers to the order and arrangement of the units
of information on a VMS (Operations office of travel
management, 1999). An example text message frame
for VMS contains many data fields such as STX,
LOCAL ID, FRAME NO, TOTAL FRAME NO,
MAIN OPCODE, SUB OPCODE, DATA SIZE,
DATA, CRC, and ETX. The following figure 1 shows
the variable message frame examples. As you can see
the figure 1, the second message frame represents
2bytes for data field but the forth message frame is
4bytes.
Figure 1: An example of variable message frame.
As you can see the example, the text message
frame has two kinds of data fields. The first kind of
data field has the fixed data type and data size.
Another has the various data type and variable data
size in a message frame. Easily speaking, the data
field has various data type and variable data size. And
we need the automatic controls generator system
which can be used to input the various data type and
variable data size of the data field using the
visualization tools. In order to generate the variable
text message frame automatically, we must generate
the data fields of text message frame on the table into
a database using visualization tool. After that, the user
must fill out the instances of the data fields with valid
value in the table. At this time, the user should know
the exact data type and data size. That is not easy
because the data fields have various data types of the
instances of the data and have variable data size of the
instance of the data. And the visualization tool is
necessary to fill out the instances of data easily and
exactly. At first, we developed the visualization tool
to generate the variable text message frame. It can
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