Dlls working in one place but not another

Hi folks,

I've been playing around with Xamarin and im hoping you can help me out with a couple of questions I have.

I can see that when you create an Android application using Xamarin you can use libraries like System.Data and System.Security.Cryptography to access SQL Server and use MD5 encoding etc.

This all works great but when I attempt to replicate the same functionality using Xamarin.Forms I am unable to do it as it doesnt seem to like System.Data.

I attempted to put the SQL Server access code in the android project of the Xamarin.Forms solution and this didnt work either.

1. So how come I can use these libraries in a Xamarin android app but not in the android project of a Xamarin.Forms project? Is it because System.Data wont work on multiple devices and that is the purpose of a Xamarin.Forms application(IOS,WP etc??)

2. If I cant use System.Data should I be using the Xamarin.Forms projects to connect to a REST webservices?

Thanks in advance.

Conor