Be very sure this is a real world issue, not just an excercise in theoretical design question on how to build a bulletproof data entry system. Over many years and some fairly high volume data entry apps I have never, not once, had to implement a locking structure to secure against simultaneous editing. I once wrote a system that kept track of the occurrence of data conflicts to assess their impact. The tracking system ran for 3 weeks and recorded 2 incidents, on a very high volume travel booking system, some twat of a manger had predicted multiple conflicts every hour. When the cost of the tracking was factored in management discarded it. So make sure you (probably some manager somewhere) are not just wasting your time on unrealistic problems. Never underestimate the power of human stupidity RAH