Element Hierarchy Extension Point & Library

The UI in Rodin 2.x contains an extension point org.eventb.ui.editorItems that groups the both following information:

• the definition of elements and attributes and their hierarchy,
• the information needed to correctly display these elements in the various editors and UI components.

It appears obvious that the first information should be defined from an extension that belongs to the Database. To fullfil the above statement, the current extension point org.eventb.ui.editorItems should be split in two.

Proposal

Hierarchy between elements

The part concerning element definition and hierarchy will go to a dedicated extension point in the database.
Here is the definition of such an extension point : org.rodinp.core.dataModel ??? or org.rodinp.core.internalElementHierarchy ???

Configuration Markup:
<!ELEMENT extension ((childRelation | attributeRelation | autoNaming)+)>
<!ATTLIST extension
point CDATA #REQUIRED
id    CDATA #IMPLIED
name  CDATA #IMPLIED
>

<!ELEMENT elementRelationship (childType)+>
<!ATTLIST elementRelationship
parentTypeId CDATA #REQUIRED
>
parentTypeId - Element type of the parent, must be the unique ID of a Rodin internal element type (see extension point org.rodinp.core.internalElementTypes).

<!ELEMENT childType EMPTY>
<!ATTLIST childType
typeId                CDATA #REQUIRED
implicitChildProvider CDATA #IMPLIED
>
typeId - Element type of the child, must be the unique ID of a Rodin internal element type (see extension point org.rodinp.core.internalElementTypes).

<!ELEMENT attributeRelationship (attributeType)+>
<!ATTLIST attributeRelationship
elementTypeId CDATA #REQUIRED
>
elementTypeId - Element type of the element, must be the unique ID of a Rodin internal element type (see extension point org.rodinp.core.internalElementTypes).

<!ELEMENT attributeType EMPTY>
<!ATTLIST attributeType
typeId CDATA #REQUIRED
class  CDATA #REQUIRED
>
Describes how to graphically display a Rodin attribute of type boolean.

attributeTypeId - Id of the Rodin attribute type to which this description applies (see extension point org.rodinp.core.attributeTypes).

<!ELEMENT autoNaming EMPTY>
<!ATTLIST autoNaming
elementTypeId          CDATA #REQUIRED
attributeDescriptionId CDATA #REQUIRED
namePrefix             CDATA #REQUIRED
>
Describes how to automatically name an element. The autoNaming definition is unique for a given element type.

elementTypeId - Element type of the element, must be the unique ID of a Rodin internal element type (see extension point org.rodinp.core.internalElementTypes).
namePrefix - default prefix to name the element

• The part concerning how to display elements and UI related info will stay in the editorItems extension point and shall point to an element definitions and hierachy.

Some identified difficulties

Initialization of elements from non UI components

The following ElementDescRegistry method, shows the dependency between an element creation and the initialization of its attributes with default values.

       public <T extends IInternalElement> T createElement(
			final IInternalElement root, IInternalElement parent,
			final IInternalElementType<T> type, final IInternalElement sibling)
			throws RodinDBException {
		final T newElement = parent.createChild(type, sibling, null);
		final IAttributeDesc[] attrDesc = getAttributes(type);
		for (IAttributeDesc desc : attrDesc) {
			desc.getManipulation().setDefaultValue(newElement, null);    // <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
		}
		return newElement;
	}

The protocol shall be changed to take into account this initialization. Doing the initialization at org.eventb.core level is possible by registering a special "attribute initializer".

---

The proposal should concern :

- Relationship declaration (new extension point)
- API to test these relations and traverse them
- Enforcement of the authorized relations when modifying the DB
- Behaviour while loading a file (including a file with invalid parent-child relations occurrences)
- What about the compatibilty with the file upgrade mechanism?