Class Diagrams

Class diagrams provide a visual representation of the structural model in BESSER. This diagram shows the static structure of a system by displaying classes, their attributes, methods, and the relationships between them.

Palette

The palette on the left side of the editor contains various shapes and elements you can use to create your class diagram. These include Classes (with or without methods), Abstract Classes, Interfaces, Enumerations, and OCL Constraints. Other elements like Associations, Generalizations, and Association Classes can be added directly from the canvas.

Getting Started

Classes

To add a class to your diagram, drag and drop a class element from the left panel onto the canvas. You can open and edit the class properties by double-clicking on the class shape:

Class properties

  • Name: The name of the class (without spaces).

  • Abstract: Mark the class as abstract if it cannot be instantiated.

  • Enumeration: Change the type to define an Enumeration.

  • Attributes: Define the properties of the class.

  • Methods: Define the behaviors of the class.

Attribute Format

Attributes can be defined using the following format:

<<visibility modifier>> <<attribute_name>> : <<data_type>>

Visibility Modifiers:

  • + Public (default)

  • - Private

  • # Protected

Supported Data Types:

int, float, str (default), bool, time, date, datetime, timedelta, any. You can also use the name of an Enumeration defined in the diagram.

Examples:

  • + age: int

  • address (defaults to public string)

  • state: StateList

Method Format

Methods can be defined with parameters and return types:

<<visibility modifier>> <<method_name>>(<<parameter_name>>: <<data_type>>): <<return_type>>

Examples:

  • + notify(sms: str = 'message')

  • - findBook(title: str): Book

  • validate()

Associations and Generalizations

To create relationships between classes:

  1. Click the source class.

  2. Drag from a blue connection point to the target class.

  3. Double-click the relationship line to edit its properties.

Association properties

  • Name: Assign a name to the association.

  • Type: Unidirectional, Bidirectional, Composition, or Generalization.

  • Multiplicity: Define cardinality (e.g., 1, 0..1, *, 1..*).

OCL Constraints

You can add Object Constraint Language (OCL) constraints to your model:

  1. Drag the OCL shape onto the canvas.

  2. Write constraints in the format Context "class_name" ....

  3. Link them to classes with dotted lines.

  4. Use the Quality Check button to validate the syntax.

Example:

Context "Person"
inv: self.age >= 0 and self.age <= 120

Association Classes

To create an association class:

  1. Drag a Class shape onto the canvas.

  2. Link it to the center point of an existing association using a dotted line.

  3. Define its attributes like a regular class.

Association Class

Code Generation

Class diagrams support generation for:

  • Django

  • FastAPI Backend

  • Full Web App (combined with a GUI diagram)

  • SQL DDL

  • SQLAlchemy

  • Python Classes

  • Java Classes

  • Pydantic Models

  • JSON Schema

  • Smart Data Models