...
Construct | Runtime instance structures | ||||||
---|---|---|---|---|---|---|---|
EClassifier Abstract superclass of EClass and EDataType | |||||||
EClass The class construct, has a name and can be abstract (cannot be instantiated) and also marked as interface (no state, just methods). A container of so-called structural features (attributes and associations). May have a list of superclasses (EClass). Example:
| Non-abstract classes can be instantiated. Instances will have attributes values and links to other objects corresponding to contained and inherited features.
| ||||||
EDataType A non-modelled or "foreign" type, provided by the host language and runtime environment, like int, double, String, Date etc. Many such types are pre-defined by Ecore, e.g. EInt, EIntegerObject, EDouble, EDoubleObject, EBoolean, EBooleanObject, EString, EDate corresponding to Java's int, Integer, double, Double, boolean, Boolean, String and Date types. You can define your own, to be able to use other Java types in your model. | Instances of the corresponding (non-abstract) Java classes can be created from Strings. | ||||||
EEnum A special kind of EDataType, where you list the set of (possible) literal values. It's similar to a simple Java enum, and a Java enum will be generated. | Instances of a generated Java enum class, that are more like values than object instances. | ||||||
EStructualFeature Abstract superclass of EAttribute and EReference. The distinction between these two is the kind of type they have, EDataType and EClass, respectively, so when adding a "property" to a class you decide which of EAttribute and EReference to use based on whether the type is an EDataType or EClass. An EStructuralFeature has a name, type (an EDataType) and multiplicity (lower and upper bounds). | |||||||
EAttribute An EStructuralFeature where the type is an EDataType.
| Both OrgUnit and Person instances have a name attribute.
| ||||||
EReference An EStructuralFeature where the type is an EClass. Corresponds to the target role of an association from the owning EClass to a target EClass. The association itself is not explicitly modelled.
|
| ||||||
Two EReferences may be each other's opposite, meaning they correspond to roles of the logically same association. This implies the consistency requirement that if one instance refers to another, the other must refer back, and vice versa.
| Consistency requirement: Since o1 has workers links to p1 and p2, p1 and p2 must both have a works-in link to o1.
| ||||||
EReferences can be marked as containment or container, to support creating strict hierarchies. A containment reference points down the hierarchy and a container reference points up. Often you have containment and container references in pairs that are each others opposites. An object can only be directly contained in one container, and this is enforced. If we model the workers EReference as containment, meaning a Person belongs to only one OrgUnit, the opposite worksIn EReference is automatically marked as container.
In general you want objects structures to be hierarchies with one root, hence containment and container markings are important. Usually you want to ensure that every class has a container EReference, unless you consider it a root object in the hierarchy. |
| ||||||
EOperation Corresponds to methods. Includes return type (EClassifier), typed (EClassifier) parameters and a list of types it may throw (EDataType).
|
...
Ecore includes a mechanism for attaching extra data to all the above modelling elements, in the form of String key-value pairs. The extra data is typically used by tools, e.g. annotations are used for naming constraints (that will need to be implemented by hand in the generated code, see Validation Constraints and validation) and providing method bodies for the code generator. You may also add your own custom annotations that are utilised by your own tools.
...
When you build an Ecore model, whether using the tree-based editor, Ecore tools diagram editor or Xcore text editor, you are actually building an object structure, a structure of so-called meta-objects (meta because they are at a conceptual level above the instances of the classes they model). E.g. in the example above, OrgUnit and Person are instances of the EClass, the name attribute is an instance of EAttribute and the workers and works-in references are instances of EReference. The figure below shows the standard class diagram notation (left) and the corresponding object diagram of the meta-objects (right).
There's a lot of detail in such a diagram, and all of them have to be right for the generated code to work as intended. A good editor helps a lot (see Editing Ecore models).
Class diagram | Object diagram of meta-objects | ||||
---|---|---|---|---|---|
|
|
There's a lot of detail in such a diagram, and all of them have to be right for the generated code to work as intended. A good editor helps a lot (see Editing Ecore models).