UML Class Diagrams: The Architectural Schematic

Vocabulary-style flashcards covering the definitions, notation symbols, and relationship types found in UML Class Diagram architecture.

UML Class Diagrams

The architectural schematic used for system architecture planning, database modeling, and bridging the communication gap between technical and non-technical stakeholders.

Attributes (Properties/Fields)

The data members of a class compartment containing visibility, name, and data type (e.g., -username: String).

Methods (Functions/Operations)

The behavior or functionality of a class compartment containing visibility, parameters, and return type (e.g., + login(): Boolean).

Public (+)

The most open visibility notation, where the member is accessible to all classes in the system.

Package/Default (~)

A visibility notation where the member is visible only to classes within the same package.

Protected (#)

A visibility notation where the member is visible only to the class itself and its subclasses.

Private (-)

The most secure/closed visibility notation, where the member is visible exclusively within the defining class.

In (Input)

A parameter direction where the parameter is sent from the caller to the method for execution.

Out (Output)

A parameter direction where the parameter is sent from the method back to the caller after execution completes.

InOut (Input and Output)

A parameter direction where the parameter is sent to the method, modified, and returned back to the caller.

Solid Line

Represents the strength of connection indicating a strong, structural, or permanent relationship such as Association or Inheritance.

Dashed Line

Represents a loose, behavioral, or transient dependency such as Usage or Implementation.

Open Arrow

A terminator indicating directionality or navigability, showing which class knows about the other.

Closed Hollow Arrow

A terminator symbol indicating hierarchy or strict inheritance ('is-a' relationship).

Diamond

A terminator symbol indicating ownership or grouping ('has-a' / 'whole-part' relationship).

Dependency

A loosely coupled connection, often called Usage, where a Client class utilizes or relies on a Supplier class to perform tasks without owning it.

Bi-directional Association

A structural link indicating that instances of two classes are connected and communication flows both ways natively.

Directed Association

A relationship with strict navigability where Class A is associated with and knows about Class B, but Class B does not necessarily know about Class A.

Aggregation

A 'Whole-Part' specialized association represented by a hollow diamond, where the child/part is independent and can exist without the parent/whole.

Composition

A 'Strict Ownership' relationship represented by a filled diamond, where the part is dependent and cannot exist independently of the whole.

Generalization (Inheritance)

Represented by the syntax 'class Child extends Parent', it is an 'is-a' relationship where the subclass acquires the structural properties and behaviors of the superclass.

Realization (Interface Implementation)

Represented by the syntax 'class Worker implements Task', where a class fulfills features defined by an interface without inheriting strict structural properties.