Cooperative Authoring
In order to enable a group of writers to create a hyperdocument together,
a number of provisions must be made:
-
Versioning is needed to allow read access to older versions while
new versions of nodes (and links) are being created.
-
Shared workspaces at the network and node level are needed.
These include individual, loosely coupled and tightly coupled modes.
-
Additional channels for meta-communication between authors are
needed (audio and video conferencing).
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:
- a list of all concurrent users displayed in the browsers;
- highlighting of objects locked by other users;
- 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.