Online Identity is an interesting topic. One way of looking at present day online identity is to think of it as being structured in a three level hierarchy. The most basic and top most level is email. It’s been around the longest and it’s the one constant required user input to register and use various web sites. With the advent of Web 2.0 and social networking, Facebook and Twitter became the two heavy-weights that comprise the second level of online identity. Many new web sites and mobile applications have moved to a model where the user may login or sign-up for the site or mobile application using their Level 2 (Facebook/Twitter) account. In other words, the user has the option of not even using an email address to login or sign-up. 

Let’s see how these different levels of online identity interact. First we’ll start with email and we’ll take a look at two popular email services: Gmail and Yahoo Mail. Here’s what the respective registration flows look like: 

Moving on to the Level 2 online identities, Facebook and Twitter, the registration process looks like:

As can be seen, a user is required to have an email account (a Level 1 identity) before they can register for Facebook and Twitter. 

Moving on to the Level 3 services/sites. Let’s consider the four following sites: Quora, Pintrest, Digg, Bitly.

So even though users can typically register for these Level 3 sites using an email address, they also have the option to login or sign-up using one of their Level 2 online identities. This is done for a couple of reasons. For one reason, the user acquisition flow is quicker. The user doesn’t have to fill out a form with their personal information in order to start using the site. They can start using the site right away. More importantly, having the user login or sign-up using a Level 2 identity gives the Level 3 site or mobile application a hook into the user’s Facebook or Twitter world. This is advantageous because it can make the overall user experience on the Level 3 site more pleasant for the end user. 

Finally, here’s a diagram I created that is a good way to visualize how these different levels interact: