How to design the member system of a website considering openID?

I am designing the database of a website and I have noticed that stackoverflow adopts openID which is very impressive. But what if some users use email address which d开发者_如何学Gooesn't support openID. What do you think of this issue?

If users don't already have an OpenID, then you direct them to an OpenID provider so they can sign up for one.

If you didn't support OpenID then your users would still have to sign up, but if you encourage them to get an OpenID then they can reuse on other sites that support it - like this one.

You have three choices when designing a login implementation for your website:

1. Support an internal login system;
2. Support an internal login system and OpenID for users that have an OpenID and don't want to register another user just to use a website;
3. Support only OpenID (That's the SO case).

For each case you have different implementations. It's up to you yo decide what is better for you website based on your community and niche. Since SO is from developers, SO developers thought it was a good idea to use OpenID - but depending on your audience (really non technical people) requiring OpenID can be worse then the login barrier itself. (This is my personal opinion about the subject)