What is the difference between httpService and Data Service

Question :What is the difference between httpService and Data Service?
Answer :The Flex presentation layer communicates with the business layer by using Flex
data services, which are objects you insert in a Flex file. Specifically, you can use Flex data services
to interact with the following:
* Web services
* HTTP services
* Remote objects
A Flex data service is an object you insert in an MXML file to communicate with the business layer
of a multi-tier application. You use data services to send and receive data from web services, HTTP
URLs, and remote objects such as server-based Java objects.
An HTTP service is nothing more than an HTTP request to a URL. The primary purpose of HTTP
services is to retrieve XML data from an external source.