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The Models are the Code Executable UML
Lecture 4 - How to Build Class Models
Paul Krause
Executable UML
Lecture 4 - How to Build Class Models
 Specifications vs Things
 Interactions
 Roles
 working within our modelling goals
 Attributes
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Specification Classes
Abstract
Aircraft Specification
Model number {I}
Stall profile
Weight
Wingspan
Fuel consumption
Properties common
to a specific aircraft type
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Concrete
Distinct
lifecycles and
properties
1
design is
specified by
R1
Aircraft
Registration number {I}
Maintenance status
specifies Assigned pilot
design of Assigned mechanic
Hours flown
0..*
Properties common
to a specific aircraft instance
Specification Pattern
Will rarely need a
state model to define
its behaviour
Will normally need a
state model to define
its behaviour
Abstract
Widget Specification
Model number {I}
Concrete
1
design is
specified by
design characteristics,
references to sub-specifications
or other related specifications
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R1
0..*
specifies
design of
Widget
Serial number {I}
characteristics that vary from
widget to widget, even when the
widgets are defined by the
same widget specification
Interaction Classes
Flight
Passenger
0..*
Name
Phone number
R1
is reserved
for
??
Seat Assignment
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Number {I}
Airline {I}
reserves Departure date
Departure time
Departure airport
Arrival date
Arrival time
??
Arrival airport
0..*
Interaction Classes
Flight
Passenger
Name
Phone number
Number {I}
Airline {I}
is reserved
reserves Departure date
Departure time
for
Departure airport
Arrival date
Arrival time
Reservation
Arrival airport
0..*
R1
Ticket number {I}
Airline {I, R1}
Cost
Class
Seat assignment
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0..*
Role Classes
0..*
R1
0..1
Wafer
Inspection Station
contains
is loaded
into
Wafer in Process
Inspection Script
0..1
Allignment
directs
Temperature
Percent scan complete scanning of
Delete once Wafer has been unloaded
from the Inspection Station
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R2
0..1
Area to cover
is scanned Scan method
according to
Relative Roles
Back Side
Front Side
APPLICATION NOTE: The flat shape can rotate in 3D space and
must have exactly one bitmap image on each of its two sides
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Multiplicity
 Remember, an important characteristic of an
association is the number of instances (objects)
that participate in each instance of the domain
relationship
 UML allows specific numbers in a multiplicity
relation
 In xUML the recommendation is to only use four
kinds:
 unconditional;
 conditional;
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1, or 1..*
0..1, or 0..*
Relative Roles
The arguments for
making this multiplicity
“2” seem compelling,
but can we work within our
modelling guidelines?
1
R1
1..*
Flat Shape
Side
can be
shown by
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can show
Colour
Texture
Two 1:1 associations?
1
Flat Shape
R1
is front of
1
is back of
1
has front
R2
1
Side
Colour
Texture
has back
But a Side is either
the Front or the Back of
a Flat Shape, not both!
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Two 1:1 associations?
1
Flat Shape
R1
is front of
1
is back of
1
has front
R2
1
Side
Colour
Texture
has back
But a Side is either
the Front or the Back of
a Flat Shape, not both!
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Two conditional associations?
0..1
Flat Shape
R1
is front of
0..1
is back of
1
has front
R2
1
Side
Colour
Texture
has back
But this says that a Side
might exist that does not
belong to any Flat Shape!
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Two conditional associations?
0..1
Flat Shape
R1
is front of
0..1
is back of
1
has front
R2
1
Side
Colour
Texture
has back
But this says that a Side
might exist that does not
belong to any Flat Shape!
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How about making the Sides attributes?
Flat Shape
Front colour
Front texture
Back colour
Back texture
?
Bitmap Image
But we need to model the association
between a Bitmap Image and a
specific Side!
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Solution: Abstract Positional roles as Classes
Side
0..*
Colour
Texture
is drawn
on
R1
1
Bitmap Image
has drawn
R4
Front Side
Back Side
has on front 1
has on back 1
R2
is front of 1
R3
is back of 1
Flat Shape
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N.B. We have worked
within our modelling
goals and produced a
better model!
What is an Attribute?
“A quality or characteristic inherent in or
ascribed to someone or something”
The American Heritage Dictionary of the English Language
Two instances of Star
Star
SAO Number {I}
Name
Diameter
Mass
Distance
Attributes:
Prototypical characteristics
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252838
Alpha Centauri
1.26 M km
1.1 x Sun
4.3 ly
131881
Sirius
4.9 M km
3 x Sun
8.7 ly
Attribute Values:
Characteristics of a specific instance
Properties of Attributes
 Purpose
 Identification role
 Dependency on other attributes
 Value assignment
 Universal meaning
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Purpose
 Here the attribute either names or describes a
class instance
 Descriptive attributes
 Size, Capacity, Colour, Stall speed
 Naming attributes
 Discovered names - Company name, Floor number,
Driver’s licence number
 Invented names - Pump ID, Transaction ID, Event ID
 Using “ID” as a suffix makes it clear these names are
the invention of an analyst
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Identification role
 Every instance of a class is unique
 Consequently, each object must have an attribute
whose value can unambiguously identify that
object
 If an attribute is marked as an identifier, then it is
constrained to have distinct values for each
instance
 In xUML there are three kinds of identifier
 implicit identifiers
 single-attribute identifiers
 compound identifiers
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Implicit identifier
location = right
zoom = 2
location = centre
zoom = 1
location = left
zoom = 1.5
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ID
Location
Zoom
CAM_1
right
2
CAM_2
centre
1
CAM_3
left
1.5
Camera
ID {I}
Location
Zoom
Implicit identifier
location = right
zoom = 2
ID
Location
Zoom
CAM_1
right
2
CAM_2
centre
1
CAM_3
left
1.5
location = centre
zoom = 1
But this identifier
is not adding anything
location = left
to the model other
zoom = 1.5
than guaranteeing
uniqueness
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Camera
ID {I}
Location
Zoom
Implicit identifier
location = right
zoom = 2
Location
Zoom
right
2
centre
1
left
1.5
location = centre
zoom = 1
We can rely on an
implicit identifier
location = left
in this case to
zoom = 1.5
guarantee uniqueness
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Camera
Location
Zoom
Implicit vs. Explicit Identifiers
 In the preceding example we were only interested
in the service each camera performed in a studio
 We
don’t actually care which precise physical camera
maps onto the class instances so long as the attribute
values are correct
 But sometimes we may need to model a real-
world identification scheme
 SAO
Number, Aircraft registration, Flight number
 In these cases we use an explicit identifier
 may consist of single or multiple attributes
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Single explicit identifier
Two instances of Star
Star
SAO Number {I}
Name
Diameter
Mass
Distance
252838
Alpha Centauri
1.26 M km
1.1 x Sun
4.3 ly
In contrast to implicit identifiers, typically the
values of explicit identifiers will not be assigned
by the model compiler
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131881
Sirius
4.9 M km
3 x Sun
8.7 ly
Compound identifiers
State
License
Colour
Year
Make
Model
Number
CA
12345
pink
1960
Cadillac
Eldorado
CA
65432
purple
1964
AC
Cobra
CO
12345
orange
1972
VW
Beetle
Licensed Vehicle
State {I}
License number {I}
Colour
Make
Model
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These two attributes
together mark a
single identifier
(State + License number)
Referential attributes
Runway
Direction {I}
Side {I}
Length
Grade
Direction Side
Length
Grade
13
Single
5000 ft
Gravel
27
Left
7000 ft
Paved
27
Right
7000 ft
Paved
But we could have
two runways with the
same value for
(Direction + Side)
at different airports
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Referential attributes
Airport
Runway
Code {I}
Current visibility
1
R1
Direction {I}
is located at is location of Side {I}
Airport {I, R1}
Length
Grade
Refers to identifier of the
associated Airport class
(the renaming is legal)
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1..*
Summary
 We have illustrated some good practice in
developing class models and their associated
attributes
 Next time we will look at the remaining properties
of attributes:
 Dependency
on other attributes
 Value assignment
 Universal meaning
 Origin
 Read Chapter 5 of Mellor and Balcer
 also Chapters 1 & 2 of Starr
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