Basic Notions

This section introduces the fundamental concepts that underpin Jjodel. Understanding these notions will help you work effectively with the platform and appreciate its design philosophy.

Models and Metamodels

In Jjodel, a model is a structured representation of real-world or abstract concepts. Models are not free-form — they conform to a metamodel, which acts as a template or “model of models.”

A metamodel defines:

• What types of elements can exist (e.g., Class, Attribute, Association)
• What properties each element type has (e.g., a Class has a name of type String)
• What relationships are valid between element types (e.g., a Class contains zero or more Attributes)
• What constraints must be satisfied (e.g., every Class must have a unique name)

Models and metamodels coexist within the Jjodel Object Model (JjOM) and are accessible through the same interface. This unified architecture is what enables Jjodel’s live co-evolution: changes to the metamodel are immediately reflected in all conforming models and their visual representations.

The Viewpoint System

A viewpoint defines a perspective on a model. It specifies how model elements are rendered, validated, or transformed. Jjodel’s viewpoint system supports:

• Syntax viewpoints — define the visual or textual concrete syntax
• Validation viewpoints — enforce constraints and business rules
• Code generation viewpoints — transform model data into code or text

Multiple viewpoints can coexist on the same model, each providing a different perspective without altering the underlying data. This is the foundation of multi-view modeling in Jjodel.

Elements, Nodes, and Edges

Jjodel distinguishes between the abstract and the visual:

• Elements are the building blocks of models: classes, attributes, associations, and other objects defined by the metamodel. They live in the abstract syntax layer.
• Nodes are the visual representations of elements in a diagram. A node defines how an element looks — its shape, color, label, position.
• Edges represent visual connections between nodes, typically corresponding to references or associations in the metamodel.

This separation means you can change how something looks (viewpoint) without changing what it is (model).

Constraints and Expressions

Jjodel supports two expression mechanisms for defining behavior, validation, and dynamic rendering:

• JjEL (Jjodel Expression Language) — a domain-specific expression language for navigating models, accessing properties, and defining computed values
• JavaScript/JSX expressions — for custom interaction logic, template rendering, and advanced computations

Constraints defined using these expressions can validate model consistency, control visual appearance, and trigger actions based on user interactions.

Live Co-evolution

Traditional metamodeling tools require a cycle of edit metamodel → regenerate code → recompile → redeploy whenever the language evolves. Jjodel eliminates this cycle entirely.

In Jjodel, the metamodel, models, and viewpoints are always synchronized. When you add a new attribute to a metamodel class, every existing model instance immediately gains that attribute. When you change a viewpoint template, the diagram updates in real time. This is possible because Jjodel’s architecture is reactive and reflective — it observes its own structure and propagates changes automatically.

Collaboration

Jjodel supports real-time collaborative modeling. Multiple users can work on the same model or metamodel simultaneously. Every action is propagated through a cloud-based publish-subscribe infrastructure, ensuring all clients stay synchronized with minimal latency.

Key takeaway

In Jjodel, three artifacts form a complete language workbench: the metamodel (what can exist), the model (what does exist), and the viewpoints (how it looks and behaves). Changes propagate live across all three.