The Web has radically transformed the way we produce and share information. It has democratized information sharing and has revolutionized how information is created and shared. It has also been through major inflection points named only software engineers would do.

Web 1.0 – Was about static pages.

Web 2.0 – Is/was about responsive, dynamic content targeted for various form factors such as mobile and tablets. It has evolved primarily into a “Mobile First” movement. Web 2.0 is also largely about User generated content and Social Media

Web 3.0 –  is about being API First. It is about IOT devices , wearable’s, smart watches, Smart devices .Building applications to cater to humans and apps alike. It is about connective intelligence, connecting data, concepts, applications and ultimately people.

With this focus on “API first”, as developers we need to worry about “How consumable is the API ? Does it follow standards ? is it secure ? How do you handle versioning ?”

There are various architectural models for developing API First systems. such as REST, SOAP, CORBA, COM, RPC etc. One of the foremost models gaining a lot of ground currently is REST. REST stands for Representational State Transfer. Rest is a client server communication model which is stateless,  resource based, and Idempotent. As an architectural model REST defines Resources, Identifiers and state representations as basic blocks.REST is not a protocol, a file format, or a development framework. It’s a set of design constraints: statelessness , Client-server etc collectively called the Fielding’s constraints.They are called so as they were first identified in Roy T. Fielding’s 2000 dissertation on software architecture, which gathered them together under the name “REST.”.In the real world REST uses HTTP as the protocol and Web servers as REST servers.

Resources – Resources are the fundamental building blocks of web-based systems. Anything that can be named can be a resource ( Person, Product, device, web page etc.). Almost anything can be modelled as a resource and then made available for manipulation over the network.The only restriction is that every resource must have a URL.On the Web, we use a URL to give each resource a globally unique address. Giving something a URL turns it into a resource.

Resources Identifiers – With so many different resources, they all should be accessible via some identity and should be identified uniquely. The web provides an URI (Unique resource identifier) for this purpose.The relationship between URIs and resources is many-to-one.A URI identifies only one resource, but a resource can have more than one URI pointing to it. A URI takes the form <scheme>:<scheme-specific-structure>. The scheme defines how the rest of the identifier is to be interpreted.For example the http part of the URI http://themoviedb.org/movie/550 indicates that the rest of the URI must be interpreted according to the http scheme. It is the responsibility of the agent listening at themoviedb.org to understand the html scheme and locate the resource identified by the reminder of the URI. URL’s and URN’s are alternate forms of URI’s. A URI that identifies the mechanism by which a resource may be accessed is usually referred to as a URL. HTTP URIs are examples of URLs. This term is now obsolete since all URI’s now need to indicate  access protocol specific information.A URN is an URI with “urn” as the scheme and is used to convey unique names within a particular “namespace.” As an example a product can be uniquely identified by this URN urn:rfidic:product:core:ACME:sku:679769.

Resource Representations – Resources can have multiple representations. A representation is a machine-readable explanation of the current state of a resource. For example one application might represent a person as a customer with an XML representation,  while another might represent the same as an image of a person in jpeg and another as the persons voice sample in an mp3 format. A resource is an information representation of a real world object/process and as such may have many representations as compared to the real world. Access to a resource is always mediated by way of its representations.This separation between a resource and its representations promotes loose coupling between backend systems and consuming applications. It also helps with scalability, since a representation can be cached and replicated.The Web doesn’t prescribe any particular structure or format for resource representations. Representations can just as well take the form of an image, a video, a JSON document or a text file.This ecosystem of formats (which includes HTML for structured documents, PNG and JPEG for images, MPEG for videos, and XML and JSON for data), combined with the large installed base of software capable of processing them, has been a catalyst in the Web’s success.

Since a resource can have multiple representations , the client needs to negotiate and indicate the representation needed by the it. There are two ways of doing this.The first is content negotiation, in which the client distinguishes between representations based on the value of an HTTP header. Using content negotiation, consumers can negotiate for specific representation formats from a service. They do so by populating the HTTP Accept request header with a list of media types they’re prepared to process. It is ultimately up to the owner of a resource to decide what constitutes a good representation of that resource in the context of the current interaction, and hence which format should be returned.The resource type returned is also always specified in an HTTP response as one of the HTTP headers (Content-Type).The second is to give the resource multiple URLs—one URL for every representation.When this happens, the server that publishes the resource should designate one of those URLs the official or “canonical” URL.

 

Putting it together- How resources, identifiers and representations driver interactions.

On the web we need to act on objects and subjects represented by resources. These resources are acted upon Verbs provided by HTTP methods.The four main verbs of the uniform interface are GET, POST, PUT, and DELETE. These verbs are used to communicate between systems. HTTP also defines a set of response codes to respond back to verbs such as 301 Moved Permanently, 303 See Other, 200 OK, 201 Created, and 404 Not Found. Together verbs and status codes provide a general framework for operating on resources over the network. You can call GET on a service or resource as many times as you want with no side effects