Layering

It seems we could express all modification in terms of Level 1 constructs

They might not be efficient but they are simple enough

Level 1

Change Transaction (CT) Structure

Changes to Attributes

• The change transaction (CT) ID. This is a reference to the ID.
• The type of change: insert, remove, modify
• The name of the attribute that is changed
• The old value of the attribute – this is not needed for an added attribute because the value will either be in the element or, if the attribute is later deleted it will be recorded there.

Changes to Elements

• Element insertion
• Element deletion

Changes to Text

• Simple text insertion
• Text insertion that flows into a new paragraph
• Simple text deletion
• Mixed content deletion

Level 2

Add an element around some existing content (insert-around-content)

Delete an element but not its content (remove-leaving-content)

Split an element into two elements (split)

Merge two sibling elements into one (merge)