Suggestions for Sync data from server to android device
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I have developed an android app and json api in php. App uses json api hosted on server to receive data which are list of products(food items) and users in app can rate those items,share e.t.c

Products are managed in php in web interface developed. 

My question is that whenever a product data changes i want apps to update those data, not every time but batch update.

And for images of products i want only those images to be downloaded by apps that have been changed.

Any Suggestions for achieving this in easy way , so that apps does not have much load in synching data...