What
A model is a representation of something else.
A class diagram is a model that represents a software design.
A model provides a simpler view of a complex entity because a model captures only a selected aspect. This omission of some aspects implies models are abstractions.
A class diagram captures the structure of the software design but not the behavior.
Multiple models of the same entity may be needed to capture it fully.
In addition to a class diagram (or even multiple class diagrams), a number of other diagrams may be needed to capture various interesting aspects of the software.
How
In software development, models are useful in several ways:
a) To analyze a complex entity related to software development.
Some examples of using models for analysis:
- Models of the can be built to aid the understanding of the problem to be solved.
- When planning a software solution, models can be created to figure out how the solution is to be built. An architecture diagram is such a model.
b) To communicate information among stakeholders. Models can be used as a visual aid in discussions and documentation.
Some examples of using models to communicate:
- You can use an architecture diagram to explain the high-level design of the software to developers.
- A business analyst can use a use case diagram to explain to the customer the functionality of the system.
- A class diagram can be reverse-engineered from code so as to help explain the design of a component to a new developer.
c) As a blueprint for creating software. Models can be used as instructions for building software.
Some examples of using models as blueprints:
- A senior developer draws a class diagram to propose a design for an OOP software and passes it to a junior programmer to implement.
- A software tool allows users to draw UML models using its interface and the tool automatically generates the code based on the model.
UML Models
The following diagram uses the class diagram notation to show the different types of UML diagrams.
source:https://en.wikipedia.org/