A special feature of the graph management is the manipulation of extents. For each used node class in the graph, there exists an Extent which collects all nodes of this class and also has a link to the extent of its superclass and to the extents of its subclasses. This feature is currently used within the RGG plug-in for a fast processing of queries which specify node type patterns like in the rule F(x) == > F(2*x);. Instead of having to scan the whole graph for nodes of class F, the corresponding extent is used together with its sub-extents to directly iterate over all nodes of class F.

GroIMP create an new extent for each type of object in the graph. Each extent keep a link with all of its direct sub extents (the extent of the sub types of nodes).

It implements the following methods:

• getType(): return the type of the node of this extent.
• getSubExtents(): return the list of extents whose type is a sub type.
• getFirstNode(): return the first element added to this extent.
• getNextNode(): return the next element in the chain.
• getTotalSize(): return the size of the extent including the size of its sub extent.

The Extent works as a linked list. When a Node is added to the graph, it is also added in the chain of the extent of this type of node. If the extent do not exist, it is created.

For instance the following graph, where RGGRoot extends Node, and Model.A extends Node:

GroIMP creates three extents, one for each type: Node, RGGRoot, and Model.A.

Extents work as linked list.