Cooperative Authoring

In order to enable a group of writers to create a hyperdocument together, a number of provisions must be made: SEPIA [SHHLSST92] is an excellent example of a hypermedia system supporting cooperative authoring. It provides a loosely coupled mode in which authors are made aware of each other via:
  1. a list of all concurrent users displayed in the browsers;
  2. highlighting of objects locked by other users;
  3. a relaxed WYSIWIS (What You See Is What I See) view: actions affecting the view of a node are private but manipulations of objects in the node become visible immediately to all other browsers if they affect the currently visible area.
SEPIA uses locking at the database level to prevent coauthors from simultaneously modifying the same object.

In tightly coupled mode the coupled browsers display a true WYSIWIS-view on the composite node's content. All actions, including scrolling and resizing, are immediately broadcast to all tightly coupled browsers.

In SEPIA the coauthors are made aware of each other's transitions from one mode of collaboration to another by means of signals. When a second author opens a composite node already "occupied" by the first author this is indicated by a "door bell" on both workstations and by a change in the user list. Authors can then select to switch to tightly coupled mode.

Whereas SEPIA tries to avoid concurrency issues as much as possible by making authors cooperate in a WYSIWIS fashion, Kock and Leggett [KWL93] explain how the concurrency problems with collaborative authoring can be described and solved in a more general way.