You can find information about PI Web Service on its user manual. Yes, there is a method to read data from AF. The best option to jump start using this product is to view this webinar and review the source code package. After doing so, you will have learned about how to use the main features of this product.
Nevertheless, PI Web API is a web service on top of the PI System and it is the recommended product for you in case you are starting a new project. PI Web Services is besed on SOAP technology while PI Web API is based on REST, which is more used by the industry. Please refer to this blog post for more information. You can download a beta version from vCampus Download Center.
Hope it helps!