I am building a web service (PHP+JSON) to sync with my iphone app. The main goals are:

1. Backup
2. Provide a web view for printing / sorting, manipulating.
3. allow a group sync up and down.

I am aware of the logic problems with all of these items, Ie. if one person deletes something, do you persist this change to other users, collisions, etc.

I am looking for just any book or scholarly work, or even words of wisdom to address common issues.

• when to detect changes of data with hashes, vs modified dates, or combination.
• how do address consolidation of sequential ID's originating on different client nodes (can be sidestepped in my context, but it would be interesting.)
• dealing with collisions (is there a universally safe way to do so?).
• general best practices.
• how to structure the actual data transaction (ask for whole list then detect changes...)