Chapter 16
UML Class Diagrams
“To iterate is human, to recurse, divine.”
- anonymous
Objectives
• Provide a reference for frequently used UML class
diagram notation.
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Introduction
• The UML includes class diagrams to illustrate classes,
interfaces, and their associations.
– “Static object modeling”
• This chapter is a reference, it summarizes the
notation, irrespective of the perspective (conceptual
or software)
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Fig 16.1 Common UML class diagram notation.
officially in UML, the top format is
used to distinguish the package
name from the class name
SuperclassFoo
or
SuperClassFoo { abstract }
3 common
compartments
1. classifier name
2. attributes
3. operations
an interface
shown with a
keyword
«interface»
Runnable
run()
unofficially, the second alternative
is common
- classOrStaticAttribute : Int
+ publicAttribute : String
- privateAttribute
assumedPrivateAttribute
isInitializedAttribute : Bool = true
aCollection : VeggieBurger [ * ]
attributeMayLegallyBeNull : String [0..1]
finalConstantAttribute : Int = 5 { readOnly }
/derivedAttribute
java.awt::Font
or
java.awt.Font
plain : Int = 0 { readOnly }
bold : Int = 1 { readOnly }
name : String
style : Int = 0
...
+ classOrStaticMethod()
+ publicMethod()
assumedPublicMethod()
- privateMethod()
# protectedMethod()
~ packageVisibleMethod()
«constructor» SuperclassFoo( Long )
methodWithParms(parm1 : String, parm2 : Float)
methodReturnsSomething() : VeggieBurger
methodThrowsException() {exception IOException}
abstractMethod()
abstractMethod2() { abstract } // alternate
finalMethod() { leaf } // no override in subclass
synchronizedMethod() { guarded }
getFont(name : String) : Font
getName() : String
...
Fruit
dependency
...
...
interface
implementation
and
subclassing
SubclassFoo
PurchaseOrder
1
...
run()
...
- ellipsis “…” means there may be elements, but not shown
...
association with
multiplicities
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Week but
7 - as
Oct.24,2005
blank compartment officially means
“unknown”
a
convention will be used to mean “no members”
...
order
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Design Class Diagrams (DCD)
• The UML has notation for showing design details in
static structure: Class Diagrams.
• The definition of design class diagrams occurs within
the design phase.
– The UML does not specifically define design class
diagram.
• The creation of design class diagrams is dependent
upon the prior creation of:
– Interaction diagrams identifies the SW classes that
participate in the solution, plus the methods of classes.
– Conceptual model adds detail to the class definitions.
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Fig. 16.2 UML class diagrams in two perspectives.
Sale
Domain Model
conceptual
perspective
Register
1
Captures
1
...
Register
Design Model
...
DCD; software
perspective
endSale()
enterItem(...)
makePayment(...)
Dr. Kivanc Dincer
time
isComplete : Boolean
/total
Sale
1
currentSale
CS319 Week 7 - Oct.24,2005
time
isComplete : Boolean
/total
makeLineItem(...)
5
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As we can see….
• A design class diagram illustrates the specifications for SW
classes and interfaces.
• Typical information included:
 Classes, associations, and attributes
 Interfaces, with their operations and constants
 Methods
 Attribute type information
 Navigability
 Dependencies
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Fig. 16.3 Attribute text vs. Association line notation for a UML
attribute.
using the attribute
text notation to
indicate Register has
a reference to one
Sale instance
OBSERVE: this style
visually emphasizes
the connection
between these classes
Sale
Register
currentSale : Sale
...
...
...
Register
Sale
1
...
currentSale
...
...
...
using the association notation to indicate
Register has a reference to one Sale instance
thorough and
unambiguous, but some
people dislike the
possible
Dr. redundancy
Kivanc Dincer
Register
currentSale : Sale
...
CS319 Week 7 - Oct.24,2005
Sale
1
currentSale
...
...
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Fig. 16.4 Idioms in association notation usage in different
perspectives.
the association name, common when drawing a
domain model, is often excluded (though still legal)
when using class diagrams for a software
perspective in a DCD
Register
UP Domain Model
conceptual perspective
UP Design Model
DCD
software perspective
time : DateTime
id : Int
Sale
Register
1
id: Int
currentSale
...
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Sale
1 Captures-current-sale 1
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time: DateTime
...
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Fig. 16.5 Applying the guidelines to show attributes in two
notations.
applying the guideline
to show attributes as
attribute text versus as
association lines
Register
Sale
1
id: Int
currentSale
...
Register has THREE attributes:
1. id
2. currentSale
3. location
time: DateTime
...
Store
1
location
address: Address
phone: PhoneNumber
...
public class Register {
private int id;
private Sale currentSale;
private Store location;
}
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How to make a DCD
• Identify all the classes participating in the SW solution by
analyzing the interaction diagrams.
• Draw them in a class diagram.
• Duplicate the attributes from the associated concepts in
the conceptual model.
• Add method names by analyzing the interaction diagrams.
• Add type information to the attributes and methods.
• Add the associations necessary to support the required
attribute visibility.
• Add navigability arrows to the associations to indicate the
direction of attribute visibility.
• Add dependency relationship lines to indicate non-attribute
visibility.
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Creating the NextGen POS DCD
• Identify SW classes and illustrate them.
Register
ProductCatalog
Store
Payment
Sale
ProductSpecification
SalesLineItem
• Draw a class diagram for
these classes.
• Include the attributes
previously identified
in the domain model.
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Creating the NextGen POS DCD (2)
• Add method names
from
interaction diagrams
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Method Names: Issues
• The following special issues must be considered with
respect to method names:
–
–
–
–
Interpretation of the create() message.
Depiction of accessing methods.
Interpretation of messages to multi-objects.
Language-dependent syntax.
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Method names: create
• The “create” message is the UML language independent
form to indicate instantiation and initialization.
• When translating the design to an OOPL, it must be
expressed in terms of its idioms for instantiation and
initialization.
Class Name
<<constructor>> SuperclassFoo(Long)
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Method names: Accessing Methods
• Accessing methods are those which retrieve (accessor
method - get) or set (mutator method) attributes.
• It is common idiom to have an accessor and mutator
for each attribute, and to declare all attribute private
(to enforce encapsulation).
• They are also called getter and setter methods.
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Method names: Multi-Objects
• A message to a multi-object is interpreted as a
message to the container/collection object
– Java’s map, C++’s map, Smalltalk’s dictionary.
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Fig. 16.6 Two ways to show a collection attribute in the UML.
Sale
SalesLineItem
time: DateTime
lineItems : SalesLineItem [1..*]
or
lineItems : SalesLineItem [1..*] {ordered}
...
...
...
Two ways to show a
collection attribute
Sale
SalesLineItem
time: DateTime
...
Dr. Kivanc Dincer
1..*
...
lineItems
{ordered, List}
...
notice that an association end can optionally also
have
a property string such as {ordered, List}
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Method Names:
Language Dependent Syntax
• The basic UML format for methods:
methodName(parameterList)
• The type of the attributes, method parameters, and
method return values may all optionally be shown.
• The design class diagram should be created by
considering the audience.
– If it is being created in a CASE tool with automatic code
generation, full and exhaustive details are necessary.
– If it is being created for SW developers to read,
exhaustive low-level detail may adversely effect the
noise-to-value ratio.
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Adding Associations and Navigability
• Navigability is a property of the role which indicates
that it is possible to navigate uni-directionally across
the association from objects of the source to target
class.
– Navigability implies visibility.
– Navigability is identified from Interaction Diagrams.
– Most, if not all, associations in design-oriented class
diagrams should be adorned with the necessary
navigability arrows.
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Showing navigability, or attribute visibility
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Association with navigability
• Define an association with a navigability adornment
from A to B:
– A sends a message to B.
– A creates an instance B.
– A needs to maintain a connection to B
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Associations with Navigability
Adornments
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Adding dependency relationships
• Dependency relationship indicates that one element (of
any kind, including classes, use cases, and so on) has
knowledge of another element.
– A dependency is a using relationship that states a change
in specification of one thing may affect another thing
that uses it, but not necessarily the reverse.
• The dependency relationship is useful to depict nonattribute visibility between classes.
–
–
–
–
Parameters
Global or local visibility
A dashed arrow line
A dashed directed line
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Dependency Relationships Non-Attribute Visibility
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Notation for Method Bodies in DCDs
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Interfaces
• The UML has several ways to show
interface implementations.
• Since both the socket line notation and
the dependency line notation used
curved lines not common in drawing
tools, most people use a dependency
arrow and the «interface» stereotype.
«interface»
Timer
getTime()
Clock1
getTime( )
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UML stereotypes
• A stereotype represents a refinement of an existing
modeling concept and is defined within a UML profile.
• UML uses stereotypes encapsulated in guillemots («
and », not << and >> ) to extend many diagram symbols.
– Guillemots can be found in the latin-1 symbol set in
Windows Insert Symbol command)
– Examples:
•
•
•
•
•
•
«interface»
«extends»
«includes»
«actor»
«create»
«destroy»
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Fig. 16.8 Stereotype declaration and use.
using the stereotype
declaring the stereotype
a tool will probably allow a popup to fill in the tag values,
once an element has been stereotyped with «authorship»
UML extension
relationship to a basic
UML metamodel term –
Element
«metaclass»
Element
«stereotype»
Authorship
author: String
status : String
...
Dr. Kivanc Dincer
«authorship»
Square
«authorship»
author = “craig”
status = “tested”
...
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Association
• An association is a structural relationship that specifies that
objects of one thing are connected to objects of another.
Navigation
• Navigability is a property of the role which indicates that it
is possible to navigate uni-directionally across the
association from objects of the source to target class.
– Navigability implies visibility.
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Dependency
• A dependency is a using relationship, specifying that a
change in the specification of one thing may affect
another thing that uses it.
the Sale has parameter visibility to a
ProductDescription, and thus some kind of
dependency
ProductDescription
...
Sale
...
...
updatePriceFor( ProductDescription )
...
SalesLineItem
1..*
lineItems
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...
...
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Figure 16.10 Showing dependency.
Public class Foo {
Public void doX( ) {
System.runFinalization( );
. . .
}
. . .
}
the doX method invokes the runFinalization
static method, and thus has a dependency on
the System class
System
...
Foo
runFinalization()
...
...
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doX()
...
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Figure 16.11 Optional dependency labels in the UML.
Window
Clock
«call»
getTime()
...
a dependency on calling on operations of
the operations of a Clock
Dr. Kivanc Dincer
B
A
«create»
...
a dependency that A objects create B objects
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Interfaces – Different Notations
socket line notation
Window1
Timer
Window1 uses the Timer
interface
dependency line notation
it has a required interface
Window2 has a dependency on the
Timer interface when it collaborates
with a Clock2 object
«interface»
Timer
Clock2
...
getTime()
Timer
Window2
Timer
Window3
getTime()
...
Clock1
implements and
provides the
Timer interface
Clock1
Clock3
...
getTime()
...
...
getTime()
...
socket line notation
lollipop notation indicates Clock3 implements
and provides the Timer interface to clients
Dr. Kivanc Dincer Timer is a provided interface
CS319 Week 7 - Oct.24,2005
Window3 has a dependency on the
Timer interface when it collaborates
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with a Clock3 object
Generalization
• A generalization is a relationship between a general
thing (called the super class or parent) and a more
specific kind of that thing (called the subclass or
child).
• is-a-kind-of relationship.
• Is this the same as OO PL inheritance?
– In donain modeling, no.
– In software modeling, yes.
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Aggregation and Composition
• Aggregation – (seldomly used)
– Whole/part relationship
– Has-a relationship
• Composition is a type of aggregation and a strong kind of whole/part
relationship:
1. An instance of the part belongs to only one composite instance at a time.
2.The part must always belong to a composite, and
3.The composite is responsible for the creation and deletion of its parts. (If
the composite is destroyed, its parts must either be destroyed, or attached
to another composite.)
1
Hand
0..7
Finger
composition
1
Dr. Kivanc Dincer
Board
composition means
-a part instance (Square) can only be part of one
composite (Board) at a time
-the composite has sole responsibility for management of
its parts, especially creation and deletion
40
Square
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Sale
1
1..*
37
SalesLineItem
Constraints
• A UML constraint is a restriction or condition on a
UML element.
three ways to show UML constraints
Stack
size : Integer { size >= 0 }
push( element )
pop() : Object
{ post condition: new size = old size + 1 }
{
post condition: new size = old size – 1
}
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Qualified Association
• A Qualified Association has a qualifier that is used to
select an object (or objects) from a larger set of
related objects, based upon the qualifier key.
(a)
(b)
Product
Catalog
Product
Catalog
Contains
1
itemID
qualifier
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1..*
1
Contains
1
Product
Description
Product
Description
multiplicity reduced to 1
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Association Class
• An association class allows you treat an association
itself as a class, and model it with attributes,
operations, and other features.
– You will see that it is necessary to use an association
class in modeling of some cases.
Company
a person may have
employment with several
companies
Dr. Kivanc Dincer
*
Employs
*
Person
Employment
salary
startDate
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Figure 16.17 Showing a singleton.
1
ServicesFactory
UML notation: in a
class box, an
underlined attribute or
method indicates a
static (class level)
member, rather than
an instance member
instance : ServicesFactory
accountingAdapter : IAccountingAdapter
inventoryAdapter : IInventoryAdapter
taxCalculatorAdapter : ITaxCalculatorAdapter
UML notation: this '1'
can optionally be used
to indicate that only one
instance will be created
(a singleton)
getInstance() : ServicesFactory
getAccountingAdapter() : IAccountingAdapter
getInventoryAdapter() : IInventoryAdapter
getTaxCalculatorAdapter() : ITaxCalculatorAdapter
...
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User Defined Compartments
DataAccessObject
id : Int
...
doX()
...
exceptions thrown
DatabaseException
IOException
responsibilities
serialize and write objects
read and deserialize objects
...
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Active Class
• An active object runs on and controls its own thread of
execution. The class of an active object is an active
class.
active class
«interface»
Runnable
run()
Dr. Kivanc Dincer
Clock
...
run()
...
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Realization
• A realization is a semantic relationship between
classifiers in which one classifier specifies a contract
that another classifier guarantees to carry out.
• We use realization in two circumstances:
– In the context of interfaces.
– In the context of collaborations.
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When to create DCDs?
Although this presentation of design class diagrams follows the creation of
interaction diagrams, in practice they are usually created in parallel.
: Register
: Sale
makePayment(cashTendered)
makePayment(cashTendered)
messages in interaction
diagrams indicate operations
in the class diagrams
Register
...
makePayment(…)
...
Dr. Kivanc Dincer
Sale
1
currentSale
classes
identified in the
interaction
diagrams are
declared in the
class diagrams
...
makePayment(…)
...
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Phases
• Inception
The Design Model and DCDs will not usually be started until
elaboration because it involves detailed design decisions,
which are premature during inception
• Elaboration
– During this phase, DCDs will accompany the UC
realization interaction diagrams; they may be created for
the most architecturally significant classes of the
design.
– CASE tools can reverse-engineer (generate) DCDs from
source code
• Construction
– DCDs will continue to be generated from the source code
as an aid in visualizing the static structure of the system
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Chapter 18
Designing for Visibility
“A mathematician is a device for turning coffee into theorems.”
- Paul Erdös
Objectives
• Identify four kinds of visibility.
• Design to establish visibility.
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Introduction
• Visibility is the ability of one object to see or have
reference to another.
Q. When is visibility necessary?
A. To send a message from one object to another, the
receiver object must be visible to the sender, so the
sender has to have a pointer or reference to the
receiver.
• Those new to object design sometimes don’t think
about and design to achieve necessary visibility.
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Q.If A sends messages to B, which must be visible to which?
A. “B is visible to A” means “A can send a message to B”.
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Visibility
• Visibility is related to the scope:
– Is one resource (such as an instance) within the scope of
another?
• The motivation to consider visibility:
– For an object A to send a message to an object B, B must
be visible to A.
How visibility can be achieved from object A to object B:
Four kinds of visibility:
• Attribute visibility - B is an attribute of A
• Parameter visibility - B is a parameter of a method of A
• Local visibility - B is a local object in a method of A
• Global visibility - B is in some way globally visible.
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Attribute Visibility
• Attribute visibility from A to B exists when B is an
attribute of A.
– Relatively permanent visibility because it persists as long
as A and B exist
– Most common form of visibility
public void enterItem(itemID, qty)
{
...
desc = catalog.getProductDesc(itemID)
...
}
class Register
{
...
private ProductCatalog catalog;
...
}
enterItem
(itemID, quantity)
: Register
: ProductCatalog
desc = getProductDesc( itemID )
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Parameter Visibility
• Parameter visibility from A to B exists when B is
passed as a parameter to a method of A.
– Relatively temporary visibility because it persists only
within the scope of the method.
– The second most common form of visibility in the OO
systems.
enterItem(id, qty)
2: makeLineItem(desc, qty)
:Register
:Sale
1: desc = getProductDesc(id)
2.1: create(desc, qty)
:Product
Catalog
makeLineItem(ProductDescription desc, int qty)
{
...
sl = new SalesLineItem(desc, qty);
...
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}
sl : SalesLineItem
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Parameter to Attribute Visibility
• It is common to transform parameter visibility into
attribute visibility
enterItem(id, qty)
:Register
2: makeLineItem(desc, qty)
:Sale
2: desc = getProductDesc(id)
2.1: create(desc, qty)
:Product
Catalog
sl : SalesLineItem
// initializing method (e.g., a Java constructor)
SalesLineItem(ProductDescription desc, int qty)
{
...
description = desc; // parameter to attribute visibility
...
}
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Local Visibility
• Local visibility from A to B exists when B is declared as
a local object within a method of A.
– Relatively temporary visibility since it persists only
within the scope of the method.
enterItem(id, qty)
{
...
// local visibility via assignment of returning object
ProductDescription desc = catalog.getProductDes(id);
...
}
enterItem
(itemID, quantity)
: Register
: ProductCatalog
desc = getProductDesc( itemID )
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Local Visibility
There are two common means by which local visibility is
achieved:
• Create a new local instance and assign it to a local variable.
• Assign the returning object from a method invocation to a
local variable.
– A variation of this method does not explicitly declare a
variable, but one implicitly exists as the result of a returning
object from a method invocation
Ex: anObject.getAnotherObject.doSomething();
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Global Visibility
• Global visibility from A to B exists when B is global to
A.
– Relatively permanent visibility since it persists as long as
A and B exist.
– The least common form of visibility in OO Systems.
• Ways to achieve global visibility:
– Assign an instance to a global variable.
– Use the Singleton pattern
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Singleton Pattern
(Gang of Four)
• Problem:
– Exactly one instance of a class is needed. Objects need a
single point of access.
• Solution:
– Define a class method that returns the singleton object,
instantiating it if it does not exist.
• Example:
– A print queue—many programs must access one queue.
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Illustrating Visibility in the UML
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Visibility in the UML
• Public:
– Any outside classifier with visibility to the given
classifier can use the feature; specified by pre-pending
the symbol “+”.
• Protected:
– Any descendant of the classifier can use the feature;
specified by pre-pending the symbol “#”.
• Private:
– Only the classifier itself can use the feature; specified
by pre-pending the symbol “-”.
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Terms: Classifier and Feature
• A classifier is a mechanism that describes structural
and behavioral features.
– Modeling elements that can have instances are called
classifiers.
– Classifiers include classes, interfaces, datatypes,
signals, components, nodes, use cases, and subsystems.
– A classifier has structural feature (in the form of
attributes), as well as behavioral features (in the form of
operations).
• A feature is a property, such as operations or
attributes that is encapsulated within entity such as an
interface, a class, or a datatype.
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Questions & Answers
Q. Which would you use if you wanted a relatively permanent
connection?
A. attribute, or global
Q. Which would you use if you didn't want a permanent
connection?
A. parameter, or local
Q. How would you create a local visibility?
A. create a new instance - use result of a method call
Q. How would you achieve a global visibility?
A. use a global variable in C++, static (or class) variable (in C++
or Java) - use the Singleton pattern (a static method that
returns the object)
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