Given two events, e1 and e2, we say e1 happens before e2, or e1 ? e2, if one of the following conditions holds: (1) e1 and e2 happen in the same process, and e1 comes before e2; (2) if e1 is the sending of a message, and e2 is the receipt of the message. The happened-before relationship is transitive; for example, if e1 ? e2 and e2 ? e3, then e1 ? e3.
Published in Chapter:
Concurrency Control in Real-Time E-Collaboration Systems
Wenbing Zhao (Cleveland State University, USA)
Copyright: © 2008
|Pages: 7
DOI: 10.4018/978-1-59904-000-4.ch015
Abstract
For all e-collaboration systems, some degree of concurrency control is needed so that two people do not step on each other’s foot. The demand for good concurrency control is especially high for the tightly coupled, real-time e-collaboration systems. Such systems require quick responses to user’s actions, and typically require a WYSIWIS (what you see is what I see) graphical user interface (Ellis, Gibbs, & Rein, 1991). This requirement, together with the fact that users are often separated geographically across wide-area networks, favors a decentralized system design where the system state is replicated at each user’s site. This places further challenges on the design of concurrency control for these systems.