Technique for multiple users on same datasets

Question

This is more a learning question than coding, but I'm certain it's a common issue for anyone developing administration systems or applications in php/mysql/js etc.

I've developed quite a complex application that lets users upload images, and define hotspots in them with associated actions. The images are stored in a table, and the actions in another, with json data for every action in a text field. However, like I say, the problem is generic.

Basically, my fear is that if someone is editing the same image and set of actions at the same time, and they both submit changes, or if it was edited by someone else then there's a whole series of structures that potentially will fail on submission.

I don't want to implement a locking system, as the system is very wide ranging (links to other images, etc), and I think it's a bit ugly. I saw this link (MSDN Multi-tenant architecture article) in another question, but it seems a little overwhelming and specialised for sql server.

So - what are the terms for data and system architecture here that I can investigate, or are there some good articles to do with this topic that people can recommend? Specifically for php/web world would be great!