In real-time distributed collaborative applications, the major areas o
f research encompass concurrency control, causal and temporal synchron
ization and real-time system response. In this paper, we propose a con
currency control model for real-time collaboration. The model is based
on the transaction concept and resolves the issue of real-time contro
l by using a distributed optimistic concurrency control protocol. It p
rovides for a flexible control mechanism by incorporating user locks u
sing the concept of persistent lock transactions. An implementation of
this model for a collaborative image design application is also discu
ssed.