What gets classified as a RESTful Web Service

Question

So I currently have an application that calls a web service to retrieve data, where I do a basic HTTP GET on a url like so www.example.com/service.asmx?param1=1&param2=2 This returns some xml which I parse.

My question is, does this classify it as a RESTful Web Service? I am thinking no, but I'd like to know what makes it a REST web-service?

I know there are REST and SOAP web services, but what would the above case be classified as, simple HTTP GET Web service? or something?

Thanks, I am trying to match terminology to concepts, forgive me if this is a bit too elementary.

Answer 1

The direct answer to your question is No.

Breaking down what you have told us about your service I will discuss what is an is not RESTful about your solution.

HTTP GET on a url like so www.example.com/service.asmx?param1=1&param2=2

You are using an HTTP GET and are therefore using one of a limited set of verbs to access some kind of resource via a URI. This is RESTful and conforms to the uniform interface constraint as long as the server does not violate any of HTTP rules about what a GET is allowed to do.

Looking at the URL itself, it is not apparent what resource you are accessing and therefore it does hint that your URL space may not be structured in a way that is convenient for doing RESTful design. However, REST does not put any constraints on what your URL should look like (despite what soooooooo many people think), so there is nothing unRESTful with your URL.

This returns some xml which I parse.

Here is where your problems start. What I am reading implicitly in this statement is that the client knows how to parse the data out of your XML. This is a violation of the Self-descriptive constraint of REST. The http message should contain all of the information that is needed for the client to know how to process the response from a request. The media-type should tell the client what information is in the XML document. If your service returns application/xml then the only thing the client knows is that the document contains attributes and elements. If the client uses out-of-band knowledge to parse that XML then you are introducing coupling between the client and the server. One of the major objectives of REST is to eliminate that coupling.

There are a number of other constraints that a service must respect in order to be considered RESTful, but you do not provide sufficient detail about your service to say one way or another if it is compliant.

Answer 2

REST services are those services which generally conform to the following:

• Provide a identifier which accurately describes the resource being requested.
• Provide services which behave as expected GET requests are Idempotent, POST updates records, PUT creates, DELETE deletes
• Minimize state being stored on the server
• Generally tear down unnecessary complexity
• Over HTTP (though I've seen other implementations, they certainly are not RESTful in the traditional sense)

The reason your URL isn't as "restful" as it could be is it contains non-identifying information (such as .ASMX). Additionally some feel that adding url parameters is only appropriate for filtering. (but that doesn't mean using URL parameters isn't RESTful!)

If it seems there are no hard and fast rules to REST, you're on the right track.

Often RESTful services deal in XML, though again, that's no hard rule by any means either.