Wireless Future - Telenor

Figure 2 The first use case diagram
for the Virtual Terminal
108
User
Initiating service
Receiving service
Using multiple devices
Configuring device
Administering the VT
example, he can move visual output from a
mobile device with small display to a larger
and better stationary screen.
• With the Virtual Terminal concept the user
can define, add or remove the devices that are
included in the large Virtual Terminal.
• With the Virtual Terminal concept the user
can set up and modify his preferences for all
devices at one place.
4 What does the User want
from the Virtual Terminal?
In a user-centric approach, we try to figure out
what the user expects from the Virtual Terminal
by elaborating use cases. Use cases are used to
describe the outwardly visible requirements of a
system [5]. Identifying the use cases of a system
is in other words equivalent to identifying what
the users require of the system.
For simplicity, we want to distinguish between
two different types of services and two types of
devices as follows:
• By communication services is meant humanto-human
communication. They can be either
synchronous (voice telephony, chat, multimedia
services, etc.) or asynchronous (e-mail,
SMS, etc.).
• Computing services or data services include
communication with machines, and these services
can also be synchronous (games, etc.) or
asynchronous (word processing, etc.).
Furthermore, a communication device is a device
offering communication services. A computing
device is a device allowing data services
and communication with other computing devices.
In addition there are other electronic devices and
peripheral devices, which can handle different
types of output and input streams, e.g. TV
screens, loudspeakers, digital cameras, microphones,
printers, scanners, etc.
The Virtual Terminal should be able to act like
a regular terminal, i.e. the user should be able to
initiate both communication and data services
via the Virtual Terminal. Likewise, he should be
able to receive incoming services on any device
included in the Virtual Terminal. The Virtual
Terminal should also be able to handle the cases
where the user wants to use multiple devices for
the input and output of his services and to control
the input and output flows. In some cases it
is also desirable to dynamically configure some
of the devices belonging to the Virtual Terminal,
which should allow the user to do this or even do
it automatically for him. In addition it should be
possible for the user to administer his Virtual
Terminal in a straightforward way. We thus
identify five main use cases, as represented by
the use case diagram in Figure 2.
These use cases are quite general, but it is possible
to go into more detail by identifying more
specific use cases, which are said to extend the
most general ones.
4.1 Initiating Services
As we have already distinguished between different
types of services, we distinguish between
initiating communication services and initiating
data services. The following three use cases
extend the initiating communication services
use case: initiating directly (the user specifies
directly the counterpart’s address or identifier),
initiating using an address book (this address
book can be contained in the Virtual Terminal
and thus be reachable from all the user’s different
devices), and initiating a group (the user
specifies a group of persons he wants to communicate
with). The extended use cases are illustrated
in Figure 3.
4.2 Receiving Services
We define three use cases extending this use
case, which cover the alternatives the user has
when receiving an incoming service request:
accepting a service request (the user wants to
accept the offered service and get it delivered to
an appropriate device – be it a local device, a
remote device or even to several devices simultaneously),
receiving in mailbox (the user does
not want to receive the service at the time of
request, but wants to record a message in his
mailbox and look at it some other time), and
refusing a service request (the user does not
want to receive the service and the request is
turned down. No connection to any of the user’s
devices is being made). These use cases are
illustrated in a use case diagram as shown in
Figure 4.
Telektronikk 1.2001