Class Relationship Summary


Properties
Categories
 Inheritance
(Generalization)		 Association Aggregation Composition Dependency
(Using, Delegation)
Semantics (meaning)
  • Is a relationship
  • A kind of relationship
  • Subclass inherits attributes & operations from superclass
  • Has a that reads well in both directions:
  • Has a relationship
  • Part of relationship
  • Build a complex whole-object from simple part-objects
  • Has a relationship
  • Part of relationship
  • Build a complex whole-object from simple part-objects
  • One object depends on another object
  • One object uses the services of another
  • An object delegates some responsibility to another
Example A student is a person. A class has a teacher.
A teacher has a class.		 A car has an engine.
An engine is part of a car.		 A car has an engine.
An engine is part of a car.		 A calculator depends on / delegates to a fraction.
A calculator uses a fraction.

Class Roles

 Parent & Child
Superclass & Subclass
Base & Derived		 Peer Whole & Part Whole & Part Dependent & Independent
Client & Server
User & Supplier
Directionality
(Navigation/Knowledge)		 Unidirectional
(Child to Parent)		 Bidirectional Unidirectional
(Whole to Part)		 Unidirectional
(Whole to Part)		 Unidirectional
(Client to Supplier)
Object Binding

Lifetimes

Sharing

 Strong
Coincident (same)
Exclusive		 Weak
Independent (distinct)
Shareable		 Weak
Independent (distinct)
Shareable		 Strong
Coincident (same)
Exclusive		 Temporary / Transient
Independent
Shared
Implementation : public 2 pointer variables 1 pointer variable 1 non-pointer variable 1 local variable

Variable(s)

N/A

 Class scope both classes Class scope whole class Class scope whole class Client function local var
Code Pattern 
class A
{
    ...
};

class B : public A
{
    ...
};
 
class B
{
   A* a;
};

class A
{
   B* b;
};
 
class B
{
    ...
};

class A
{
   B* b;
};
 
class B
{
    ...
};

class A
{
   B b;
};
 
class A
{
public:
   void func(B b) {}
   void func(B* b) {}
   void func(B& b) {}
};
Return type not significant
UML Class Relationship Symbol Solid line with a hollow, three-sided arrowhead. Solid line without decorations. Solid line with a hollow, four-sided diamond at one end. Solid line with a solid, four-sided diamond at one end. Dashed line with an open arrowhead at one end.

 

 

Relationship Table Legend: Properties and Values

Property Values Meaning
Semantics1 Is a, Kind of One object is another object (possible to substitute one object for another). One object is a (special) kind of another (general) object.
Has a, Part of One object has another object as a part. One object is a part of another object. One object contains another object.
Depends on One object depends on (uses, delegates some responsibility to) another object.
Directionality2 Bidirectional Messages are exchanged in both directions (i.e., both objects may send a message). Possible to go from either object to the other. Both objects "know" about each other.
Unidirectional Messages are sent in only one direction (i.e., only one object sends a message). Possible to go from one object to another but not in the opposite direction. Only one object "knows" about the other.
Binding3 Strong/Tight Lifetime (Coincident) Object lifetimes are the same: they are created and destroyed at the same time.
Sharing (Exclusive) Objects form an exclusive relationship that does not permit sharing of the parent or part object.
Weak/Loose Lifetime (Independent) Object lifetimes may be different: they may be created and destroyed when convenient (at the same or at different times).
Sharing (Shareable) Whole objects may share their pars with other objects in the program/design.
Temporary/ Transient Lifetime (Independent) Object lifetimes are different: The client passes an existing object (itself or one of its parts) as an argument to a supplier function's parameter, which the function destroys when it returns.
Sharing (Shareable) Parameters passed by pointer or reference are shared; parameters passed by value or non-parameter, local variables are not.