The Unified Modelling Language UML

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The Unified Modelling Language (UML)
Conceptual modelling
Class diagrams (continue) Illustrative
case-studies Specifications Use-case
diagrams Discovering objects Conceptual class
diagram
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The Unified Modelling Language
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Relationships between classes
Other forms of notation frequently used are
- Role names on associations - Interface
inheritance (implements) - Uses
relationship- Generic instantiation
type
collection
ltltbindgtgt book
Book list
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The Unified Modelling Language
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Illustrative case studies
To demonstrate and practice the methods used in
OOD, the following two very different case
studies will be used throughout the
course. Motorway toll system This is a large,
distributed, real-time system which is concerned
with the automatic collection of tolls
on motorways. Diagram editor In contrast,
this forms part of a CASE tool GUI and
is concerned with the drawing of diagrams with
specific properties.
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Motorway toll system
Toll gantries will be sited at strategic points
along the motorways. These are equipped with
radar sensors, radio transceivers and cameras.
Every car will be equipped with a radar
transponder as used in aircraft and when sensing
the radr beam will emit a signal which identifies
the driver and the current balance on his
account. This is achieved by providing drivers
with magnetic cards which are inserted into the
transponder and provides a unique identity for
the owner of the card. The card also contains a
record of the current credit on the drivers
account. As the car passes the gantry, a
broadcast signal informs the in-car system of the
fee payable and the transponder deducts that
amount from the current balance. The transaction
is also relayed back to the regional centre where
information on toll charges is passed to a
central system which maintains drivers
accounts. The transponder is preset to
identify the type of vehicle so that different
toll charges can be made for different types of
vehicle. Magnetic cards can be checked and
topped up at payment machines sited in post
offices. From here the payment details are
transmitted to the central system to update the
drivers account. If a car is detected which does
not respond due to faulty or absent transponder
or card, the camera is activated to take a
picture of the car registration. This is done
with a digital camera and the resulting image
processed to extract the number which is sent
along with time and date to regional centre. If
the account becomes overdrawn, no picture is
taken. The traffic events which record location
and direction of travel are used at the regional
centre to monitor traffic densities and identify
trouble spots. A constantly updated display of
the road network is provided for traffic
advisory radio service to supplement their
closed-circuit television monitoring. Also, usage
statistics on traffic flows are recorded every
hour to assist planning of maintenance and new
roads.
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Diagram Editor
This is a specialised style of diagram editor for
drawing system models as a block diagram. A
diagram consists of a number of separate
sub-diagrams, each of which consists of a number
of boxes of different types connected by directed
lines. Boxes have a number of lines leading to
them (inputs) and coming from them (outputs).
Lines consist of one or more straight line
segments with an arrow indicating the direction
of flow through the model. Boxes are of one of
the following types - Start boxes (one
per sub-diagram) - no inputs and only one ouput
line. Normal process boxes - up to ten
inputs and one output. Branch boxes
representing decision points with up to ten
inputs and up to ten outputs. Terminal
boxes with up to ten inputs and no
outputs. Boxes are divided into two
compartments, a left side and a right side.
During development, boxes can exist within the
diagram unconnected or partially connected. Lines
however must always connect tow boxes and cannot
exist on their own. In normal edit mode, as the
cursor passes over a box it changes colour to
show that it is selected. The effect of mouse
button clicks when the cursor is over a box are
as follows (lbd left button down event etc)
Cursor in left of box lbd - bring up a dialog
box allowing contents of box to be altered or
box to be deleted -
in latter case all lines to or from boxes
are also deleted. Cursor in left of box
rbd - box is dragged to a new position, when rbu,
fixed in new position and lines redrawn.
Cursor in of bax lbd - start drawing a line
from right side of box and other end follows
cursor. During line
drawing, left button down events produce
anchor points for line segments unless over a
different box,
when line drawing is completed and the new line
replaces any previous one
editor returns to edit mode.
While drawing line, rbd causes line drawing to be
cancelled. Cursor in right of box rbd -
only with branch box, a new ouput is selected
from the ten available. When no box selected
lbd, dialog box pops up to allow the creation of
a new box.
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Use-case for motorway toll system
Underpaid transaction
Record illegal use
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Create transaction
Record traffic event
Charge card
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Discovering Objects
Probably the most difficult part of OOD. No
right answers - only better or poorer
ones. Look for candidate objects as nouns in the
system descriptions. Be very wary of inferred
nouns. Need to read between the lines. Objects
have state and suffer or perform
actions. Actions on objects bring about changes
of state of the object. Objects will represent
key concepts in the application domain. From
identification of objects we can infer candidate
classes.
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Candidate classes for the motorway toll system
System toll motorway motorist toll
booth payment strategic point toll gantry radar
receiver transmitter camera car transponder radar
beam signal driver vehicle current
balance balance account
Transaction regional centre toll central
system magnetic card payment machine post office
country customer balance valid card credit
balance picture registration plate computer
registration number image location time offence
card negative a/c balance
Fee underpaid transact warning signal traffic
event gantry direction information traffic
density route trouble spot hold up display road
network feature traffic advice service closed
circuit TV traffic channel usage
statistics traffic flows segments hour of the
day new road maintenance operation
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Deriving principle classes - refinement
The list of candidate classes will be excessively
long and contain many inappropriate items. These
should be filtered out by applying the
following criteria - Classes outside
scope of system Redundant classes -
synonyms Vague classes
Implementation classes Attributes of
other classes Verbs or events
Representing entities over which the system will
have no control. Different names referring to
the same concept. Non-specific concepts too
imprecise to define exactly. Parts of the final
computer system rather than the user
domain. Simple data values not warranting treatmen
t as an object - keep a note. Possibly methods in
other classes
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Classes outside the scope of the system
System toll motorway motorist toll
booth payment strategic point toll gantry radar
receiver transmitter camera car transponder radar
beam signal driver vehicle current
balance balance account
Transaction regional centre toll central
system magnetic card payment machine post office
country customer balance valid card credit
balance picture registration plate computer
registration number image location time offence
card negative a/c balance
Fee underpaid transact warning signal traffic
event gantry direction information traffic
density route trouble spot hold up display road
network feature traffic advice service closed
circuit TV traffic channel usage
statistics traffic flows segments hour of the
day new road maintenance operation
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Redundant classes - synonyms
System toll motorist customer toll
booth payment strategic point toll gantry radar
receiver transmitter camera car vehicle
motorist radar beam signal driver
motorist vehicle current balance balance
current bal account motorist
Transaction underpaid regional
centre toll central system magnetic card
card payment machine customer balance valid
card credit balance picture registration
plate computer registration number
plate image location time offence card valid
card negative a/c balance
Fee underpaid transact warning signal traffic
event gantry toll gantry direction information t
raffic density trouble spot hold
up display feature closed circuit TV usage
statistics traffic flows hour of the day
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Vague classes
System toll motorist toll booth payment strategic
point radar receiver transmitter camera radar
beam signal
Transaction regional centre central
system magnetic card payment machine credit
balance picture computer registration number
image location time offence
Fee warning signal traffic event gantry
direction information traffic density trouble
spot hold up display feature closed circuit
TV l usage statistics traffic flows hour of the
day
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Implementation classes
System toll motorist toll booth payment radar
receiver transmitter camera signal
Transaction regional centre central
system magnetic card payment machine credit
balance computer registration number
location time
Fee warning signal traffic event gantry
direction traffic density display closed
circuit TV l usage statistics traffic flows hour
of the day
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Attributes of other classes
toll motorist payment radar
receiver transmitter camera signal
Transaction regional centre central
system payment machine credit balance
registration number location time
Fee warning signal traffic event gantry
direction traffic density usage
statistics traffic flows hour of the day
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Verbs or events
motorist payment radar receiver transmitter
camera signal
Transaction regional centre central
system payment machine
warning signal traffic event gantry

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Final class list
motorist radar receiver transmitter camera

Transaction regional centre central
system payment machine
gantry
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Final class list - Motorway toll system
Motorist account holder radar transceiver sub
system detecting communicating with
transponder camera digital camera for
recording and relaying registrations transacti
on vehicle passage through toll -
time,direction fee, account ID regional
centre collect and analyse traffic
flows central system update accounts payment
machine recharging card with credit - link to
central system. Gantry assembly of
components.
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Conceptual model - motorway toll system

Central System
Regional Centre
updated by
Gets traffic events from

Toll gantry
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records
Traffic lane
Transaction

Radar
Camrea
Radio transceiver