Resource

We can identify the types of properties, functional property, which expresses "what" we get from service; quality of the service, referring to characteristics (for example, delivery time) that specify benefits or perceived utility associated with the service; non-functional properties, expressing "how" the service is delivered to us.

Reference Representation, Narrow Representation, Wide Representation

A resource has some state and zero or more sub-resources. Each sub-resource can be either a simple resource or a collection resource.

The key characteristic of a resource-oriented API is that it emphasizes resources (data model) over the methods performed on the resources (functionality)