What is the logic to send friend requests and showing notifications?
<p>What is the logic to send friend requests?</p>

<p>I want that with my application's user is able to search for other users and be able to send friend requests to them. I have two tables in my database. One is for user information and another is friendships which stores user id and friends id.</p>

<p>My application is combination of an Android client and PHP web server. In addition, how can I display notifications to a user about his friends' current activities?</p>
