Rest – How is oData different from a REST service

Why do we need to give Gmail — or any other site with user accounts — our username and password if it's already using HTTPS? The answer is the same as the answer to your question.

HTTPS provides, first and foremost, an encrypted connection between the server and the client.

The trust inherent in HTTPS is based on major certificate authorities that come pre-installed in browser software (this is equivalent to saying "I trust certificate authority (e.g. VeriSign/Microsoft/etc.) to tell me whom I should trust").

Unless the server gives each user a certificate, the server can't trust the client without some other method of authentication.

Web API does odata. See Scott Guthrie's blog post. Specifically:

Query composition: Web API enables you to easily support querying via the OData URL conventions. When you return a type of IQueryable from your Web API, the framework will automatically provide OData query support over it – making it easy to implement paging and sorting.

I'd also think that in many cases the same class could be the traditional WCF class and the Web API class, they are definitely not mutually exclusive.