Manual

Metamodel

In Jjodel, a metamodel is a structural and semantic framework that defines the abstract syntax for a modeling language. It provides the blueprint for what concepts and elements are valid within a model, as well as how these elements can be interrelated. In Jjodel, the metamodel functions as the backbone of a modeling project, allowing for the creation, manipulation, and validation of models based on a consistent and structured set of rules. The metamodel encapsulates the vocabulary and constraints of a domain, making it an essential component for any model-based application in Jjodel.

The main components and features of a metamodel in Jjodel are the following

Defining Model Elements

 

• – In Jjodel, classes represent the core types or entities in a domain. Each class defines a type of element that can be instantiated in a model. For example, in a UML-like modeling language, classes might represent concepts like Class, Attribute, or Operation.
• – Each class can have attributes, which define the properties or characteristics of that class. Attributes specify the data or values that an instance of the class will store. In Jjodel, attribute types can include primitive types (e.g., String, Integer) or custom types defined in the metamodel.
• – References define relationships between classes. For instance, in a UML diagram, a Class may have references to other “Classes” (as associations) or to “Attributes” (as owned features). References in Jjodel metamodels can have multiplicity constraints, such as one-to-one, one-to-many, or many-to-many relationships, defining how instances can relate to each other. 
• – A Jjodel metamodel can be organized into packages, which logically group classes, references, and attributes by functionality or domain. Packages support modularity, making complex metamodels easier to manage and navigate.

In the following figure, a simple metamodel is presented that consists of three concrete classes (Class, Operation, Attribute) that inherit from an abstract class (namedElement) that has an attribute, name, whose type is EString. Finally, the references, ownedAttributes and ownedOperations, in Class are two compositions (denoted by the black diamond egde) that make Class a container for both attributes and operations.

Among the features, Jjodel allows metamodels with Singleton classes, i.e., classes that are automatically instantiated in models only one. For instance, in the following

the classes Integer, String, and Boolean, will be automatically instantiated once and only once in conforming models as in the following model where the instances corresponding to the singleton instance are denoted by the

icon

 Inheritance and Hierarchies

  

• – Jjodel supports (multiple) inheritance in the metamodel, enabling a class to inherit attributes and references from a parent class. This feature promotes reuse and modularity by allowing shared properties and relationships to be defined in base classes and extended by subclasses. In the above diagram, the class Class extends the class namedElement
• – In Jjodel, classes can be marked as Abstract, indicating that they cannot be directly instantiated. Abstract classes are typically used to define general characteristics that are inherited by more specific subclasses, organizing the metamodel into a logical hierarchy. The class namedElement is abstract, i.e., it cannot be instantiated.

Validation

Jjodel allows for the definition of validation rules on model elements within the metamodel by means of Validation Viewpoints. These constraints are used to enforce business rules and domain-specific logic, such as ensuring that an association only exists under certain conditions, that a value falls within a defined range, of that the name of a feature satisfies certain conventions. In essence, validation within the metamodel enables validation of models, ensuring that instances comply with both structural and behavioral requirements. Validation is essential for catching errors early and maintaining model integrity.

 

Jjodel has a default validation viewpoint

 

 

that consists of three views, the first for rendering the notification message in case of violation of the validation rules, the other two checking the lowerbound cardinality for attributes and references, and the name composition, respectively.

 

A Jjodel metamodel serves as a schema, and the elements within it define the types for instances created in models. The metamodel enforces the rules governing these instances, ensuring that they adhere to the defined classes, attributes, and references.