Common Mechanisms of UML

Behavioral Things

They model what the system does over time and space

These are verbs of the UML models

They usually are the dynamic parts of the system in question. There are two types of behavioral things

Interaction State Machine

Interaction:

Interaction is a behavior that comprises a set of messages exchanged among a set of objects to achieve a particular purpose

Each message in the interaction is represented as a directed line

State Machine

State machine is a behavior that specifies the sequence of states an object goes through, during its lifetime in response to events

Each state in the state machine is represented as rounded rectangle

Grouping Things 

• The model of a complex system will have a huge number of elements or things and to make it manageable, these elements have to be grouped meaningfully 
• Each of these groups is called as ‘package’.

Package:

• Package is a namespace used to group together elements that are semantically related and might change together 
• A package may contain structural, behavioral and other grouping things

Annotational Things

• Annotational things are explanatory parts of UML models. They are the comments used to describe or provide remarks about any element in a model. A node is an annotational thing 

Node: 

• A node is a graphical notation for attaching constraints and/or comments to elements of the model 
• It is represented as a rectangle with a dog-eared corner 

Relationships 

• In understanding complex systems, it is important to model how different elements are related to one another. This is done through relationships 
• There are four types of relationships in UML 

Dependency Association Generalization Realization

Dependency

• Dependency is a relationship between two things in which changes to one thing (the independent thing) will impact another thing (the dependent thing) 
• It is represented as directed dashed line

• Association is a structural relationship among classes that describes a set of connections among objects of those classes 
• Association may specify a name and each end of a relationship may specify a role, multiplicity, visibility, etc. 
• It is represented as solid line

Generalization:

• It is a kind of relationship in which the specialized element (called Child) builds on the specification of the generalized element (called Parent) 
• The Child element shares the structure and behavior of the parent 
• It is represented as a solid line with a hollow arrowhead pointing to the parent

Realization

• Realization is a relationship between two things, in which one thing realizes the behavior that the other thing specifies 
• Example: "A Collaboration realizes a Use Case." i.e., the Use Case specifies the behavior (functionality) to be carried out (provided), and the collaboration actually implements that behavior 
• It is represented as a hollow diamond shape