Deletion

Overview

• This page is intended to explain how deletion works in the framework and our specific implementation for UCMs.

Framework

• DeletionAction is added to our context menus / keybindings (See Dev Doc Actions)
• Our ComponentEditPolicies located in seg.jUCMNav.editpolicies.element all have a getDeleteCommand(GroupRequest request) method.
• Given an editpart's component editpolicy, specify which command to run when delete is pressed/selected.

Base Elements

• We need to be able to delete any PathNode from its path. See DeletePathNodeCommand
  • 1 in / 1 out: is removed from the path
  • Multiple in or out: disconnect all branches
    • Might require deleting the element or downgrading it into an empty point. See DoesDisconnectImplyDelete
• We need to be able to delete a Path, starting from its end point or start point. See DeletePathCommand and Dev Doc Algo Deletion
• Implicit deletion: When performing some transformations, such as merging a StartPoint and an EndPoint, elements are deleted and their properties must be removed.

Major issues

• Our original implementation used adhoc ways to get rid of certain information when deleting. We pretty much duplicated the code everywhere to, for example, remove InBindings/!OutBindings from
• We did a good job implementing all this during explicit deletions, but we could not assure the uniformity with transformation commands.
• When doing certain transformations, we not only need to delete the information, we sometimes need to move it. This is the case with NodeConnections around a Stub or after a Timer/!WaitingPlace/OrFork. If we insert a new node connection in between of the original one and the PathNode, we need to move plugin bindings, conditions, etc.
• As a solution, we implemented a few CompoundCommands that are intended to be used everywhere an element must be deleted, so that we don't end up with model relationships that have not been broken.

Our implementation

• See Dev Doc Algo Deletion for an overview of the algorithms.
• See Dev Doc Deletion Tests for an overview of the desired behaviour.
• The hardest part about deletion commands is that they can be run simultaneously in a large CompoundCommand built by the DeletionAction. One intuitively builds a GEF CompoundCommands by adding regular Commands during its constructor. However, we often cannot do this because the state of the model will change between the constructor and the execute() method. We therefore had to wait as long as possible before building our commands, by overriding canExecute() and execute().
• What follows is a brief hierarchical overview of what is in both packages

Commands

• PreDeleteUcmModelElementCommand : This command prepares an element for deletion.
  • CleanRelationshipsCommand : Removes all invisible relationships related to a NodeConnection, PathNode or ComponentRef.
    • RemoveLinkedInfoCommand : Given a ComponentRef, PathNode, NodeConnection or Map, remove its performance/scenario information
    • ComponentRefUnbindChildCommand (to disconnect from parent)
    • ComponentRefUnbindChildCommand (to disconnect children)
    • DeleteBindingsCommand : Given a PathNode, NodeConnection or Map, removes anything to do with Stub-Plugin bindings.
  • DisconnectCommand:
    • Disconnects synchronous and asynchronous connections

• PrePathManipulationCommand: Manipulates the path to prepare to remove this PathNode.
  • DisconnectBranchesCommand: Given a PathNode, disconnect all relevant branches.
  • RewirePathCommand: Given a PathNode with one input and output, removes the outgoing node connection and rewires the incoming node connection onto the successor.

• RemoveUcmModelElementCommand: Given a PathNode or ComponentRef, remove it from the map or pathgraph, the component ref binding hierarchy and disconnect it from its definition if it is a responsibility

• PostPathManipulationCommand: Intented to be used after the deletion of a PathNode which must be downgraded to an EmptyPoint
  • SplitLinkCommand: Insert an empty point at the deletion location, if necessary.

• DeletePathNodeCommand: Deletes any PathNode from the model.

• • PreDeleteUcmModelElementCommand
  • PrePathManipulationCommand
  • RemoveUcmModelElementCommand
  • PostPathManipulationCommand

• • DeletePathCommand: Given a StartPoint / EndPoint, find the deletion path using the query infrastructure and delete the whole path
    • infer the affected nodes using the deletion path query
    • DeleteBranchesCommand on extremity: This command will delete the branches from a PathNode.
    • DeletePathNode on all PN/NC in set, except extremities
    • DeleteStartNCEnd on last elements: This command will remove a simple path from the map.

-- Jason Kealey - 14 Jul 2005