The resource-oriented design section intends to walk you through the ROA design guidelines, design principles, and characteristics, along with its properties as well. Having introduced ROA properties, we will look at REST architecture in subsequent sections.

ROA-based web services describe a self-discoverable entity, and modeling is based on its logical form (unlike services, as they are based on the technical form).

Let's look at the basic blocks of ROA such as resources, representations, and so on in the following diagram:

The blocks in the preceding diagram represent the typical structure of ROA and give an idea of how resources are consumed by the service consumers.

Let's briefly consider the concepts and properties of ROA, as follows:

• Resource providers: Resource providers expose the resources for the service consumers to invoke the services with HTTP methods. Microsoft Azure and Amazon AWS are simple examples of resource providers.
• Resource: A resource is an explicit reference to an entity that can be identified and assigned and, most importantly, referenced as a resource. Some examples of resources could be servers, devices, web pages, JavaScript, or the latest version of software, the latest defect in software, a directory or list of information about an organization, and so on.
• Resource name: The resource name is the unique name or identification for the resource. So, no two resources can point to the same data. For instance, the latest version of software is 2.0.9.
• Resource representation: Resource representation is the useful information about the current state of a resource, specified with a specific format, in a specific language.
• Resource link and connectedness: Represents (linkage) another resource or the resource itself. Connectedness is all about how reliable and relevant the resource's links are.
• Resource interface: The resource interface is an interface for accessing the resource and handling its state.
• Addressability: Addressability is exposing datasets or functionalities as a resource, and the addressability of a resource happens through URIs.
• Statelessness: Statelessness is maintaining the isolation and independence of client and server states. Every request from the client should be self-contained.
• The uniform interface: Every service needs to use the HTTP interface the same way, such as GET, POST, PUT, DELETE, and so on. The uniform interface simply means using some common nomenclature that is interpreted the same way across the web. For example, GET does mean get (read) something.

The following table summarizes the HTTP operations that can be used to implement an ROA-based web service:

The preceding table shows the HTTP methods to implement ROA.