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Class and Sequence diagrams
UML notation
SE-2030Dr. Mark L. Hornick
1
Domain modeling will identify multiple classes
Taken together, a class diagram gives a good overview of a system’s structure
Including how the various classes are related to one another
SE-2030Dr. Mark L. Hornick
2
Identifying class relationships
Go back to the Use Cases, and look for possessive terms relating one object to another “account’s credentials” “order’s entries” “path’s coordinates”
SE-2030Dr. Mark L. Hornick
3
Possessive terms usually indicate a stronger form of relationship thana simple association
Many classes within an application usually exhibit some type of Association between one another
Associations represent permanent relationships between instances of classes:An Order has Entries
An Order is billed to an Account
A Login Screen is a type of Dialog
An Invoice corresponds to each Order
SE-2030Dr. Mark L. Hornick
4
A Simple Association merely shows a general-purpose relationship
SE-2030Dr. Mark L. Hornick
5
class Class Model
Inv oice Order
The single-line connector doesn’t indicate anything specific – thatis, it’s an unspecified association.
About all we can say is that objects of these classes are somehow interrelated – perhaps an Invoice somehow holds a reference to an Order object (or vice versa).
An association can indicate multiplicity – that is, how many objects of one class correspond to objects of the other
SE-2030Dr. Mark L. Hornick
6
This association indicates that there is a one-to-one correspondence between Invoice instances and Order instances; that is, for every Invoice object, there is a corresponding Order object, and vice versa.
class Class Model
Inv oice Order
1 1
Associations can indicate various degrees of multiplicity
SE-2030Dr. Mark L. Hornick
7
This Simple Association indicates that for every Order object, there is at least one corresponding Entry object.
Here, any number (including zero) of Entry objects correspond to each Order object
class Class Model
Order Entry
1 1..*
class Class Model
Order Entry
1 *
Associations can indicate navigability – that is, whether an object holds a reference to the other
SE-2030Dr. Mark L. Hornick
8
This one-way association indicates that an Invoice object holds a reference to a single Order object.
class Class Model
Inv oice Order
1 1
class Class Model
Inv oice Order
1 1
This bi-directional association indicates that Invoice and Order objects hold references to each other.
End Roles indicate that an association is maintained via a specific attribute defined within a class
SE-2030Dr. Mark L. Hornick
9
This one-to-one, one-way association with End Role acct indicates that an Order object holds a reference to a single Account object via a private Account attribute named acct.
Here is a less illustrative way of showing the same relationship.
class Class Model
Order
- acct: Account
Account
class Class Model
Order Account
1
-acct
1
End Roles can indicate specific bi-directional references
SE-2030Dr. Mark L. Hornick
10
This bi-directional association indicates that an Order object holds a reference to a single Account object via a private Account attribute named acct, and that an Account object holds a reference to a single Order object via a private Order attribute named ord.
class Class Model
Order Account-ord
1
-acct
1
Here is a less illustrative way of showing the same relationship.
class Class Model
Order
- acct: Account
Account
- ord: Order
Associations can imply that a reference is a collection of objects
SE-2030Dr. Mark L. Hornick
11
This one-way association indicates that an Order object holds a reference to a collection of zero or more Entry objects via a private attribute named items.
The same association, less illustratively.
class Class Model
Order Entry
1
-items
*
class Class Model
Order
- items: ArrayList<Entry>
Entry
Stereotypes indicate a logical function of an association
SE-2030Dr. Mark L. Hornick
12
This stereotype specifies “containment” of an collection of Entry objects by an Order object.
Stereotypes are usually verbs that indicate the specific type of usage.
class Class Model
Order Entry
1 «contains»
-items
*
Composition is a stronger form of an association that implies containment and lifetime
SE-2030Dr. Mark L. Hornick
13
By “stronger”, we mean that the semantics of the association are more specific.
Composition indicates that the Entry objects cannot exist independently of the Order object; that is, if the Order object is deleted, all the Entries are deleted as well.
class Class Model
Order Entry+items
*1
Aggregation is a stronger form of an association that implies containment, but not lifetime
SE-2030Dr. Mark L. Hornick
14
Aggregation indicates that the Order object can exist independently of the Invoice object; that is, if the Invoice object is deleted, the Order can still exist (maybe it can be fulfilled free of charge).
However, the Composition association in the other direction indicates that if an Order is deleted, the associated Invoice must be deleted as well (you shouldn’t invoice someone for an Order that doesn’t exist!)
class Class Model
Inv oiceOrder
-inv
11
+ord
1 1
Inconsistent terminology between strict UML and EA
UML Aggregation A is composed of B; B can exist
without A EA refers to this as Shared
Aggregation
UML Composition A is composed of B; B cannot exist
without A EA refers to this as Composite
Aggregation
SE-2030Dr. Mark L. Hornick
15
Generalization is another form of association that implies that a class inherits behavior defined and implemented in another class
SE-2030Dr. Mark L. Hornick
16
Here, the Generalization association implies that the LoginClass inherits the behavior (and attributes) of the JFrame class. Objects of the LoginClass are also JFrame objects.
class Class Model
JFrame LoginScreen
class Class Model
JFrame
LoginScreenGeneralization can be illustrated in the alternate notation shown if the parent class is not present in the class diagram
Realization is a form of association that implies that a class implements, but does not inherit, the behavior defined in another class
SE-2030Dr. Mark L. Hornick
17
Here, the Realization association implies that the LoginClass implements the behavior of the Serializable class (which in Java is called an Interface). Objects of the LoginScreen class are also Serializable objects.
class Class Model
LoginScreen«interface»Serializable
In EA, the Association Properties dialog controls the semantics of an association
SE-2030Dr. Mark L. Hornick
18
Showing recursion in a Sequence Diagram
SE-2030Dr. Mark L. Hornick
19
sd Sequence
anInvoice :Invoice :EntryanOrder :Order
*[foreach( Entry in Order)]: entry= getEntry() :Entry
getInfo()
getOrderID()
Showing selection in a Sequence Diagram
SE-2030Dr. Mark L. Hornick
20
sd Sequence
anInvoice :Invoice :EntryanOrder :Order
*[getFirstEntry]: entry= getEntry() :Entry
[if( entry != null )]:getInfo()
getOrderID()
[if( entry == null )]:reset()