RESTful Web Services Part 2 - Characteristics

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1. Resources

A resource is a thing that:

is unique (i.e., can be identified uniquely)
has at least one representation
has one or more attributes beyond ID
has a potential schema, or definition
can provide context, and
is reachable within the addressable universe

A resource can be practically anything:

A blog post
A collection of blog posts
An image
A user
Map coordinates
A bank transaction
Search results
Documents
People
Places
Abstract Concepts (e.g. processes,transactions)

A resource can be explored to:

Web Side
Resume
Aircraft
A Song
An Employee
A Transaction

Not Resource* - Even these could be resources in the right context, but you have to stretch some to find it:

Mailing Address
$32.76
A Gallon of Gasoline
Love

2. Representations

A representation is a description of a resource that is used for some computational purpose. Representations can be thought of as models of the resource is question, and as is the case with any modeling, a given resource may have any number of distinct representations.

A Kitten
Some Text
Name:Bob
Breed:Tabby
……
A Picture/A Drawing/A Haiku/A BlogPost
HTML
- <!DOCTYPE html>
- <html lang=“en”></html>
Video

3. Representational State Transfer

A representation shows a reflection of the state of a given resource in a given form
This “representational state”collapses to the resource description itself when the resource is static, but will change if the resource itself changes
The transfer of this representational state between nodes in the network is the fundamental operation of the web

4. Addressability

Every resource has at least one URI; every URI points to a resource.

http://example.com/entities/2012/02/restful-web-services
http://example.com/tags/awesome
http://example.com

5. Idempotency

Being able to perform an operation multiple times without changing theresult after the initial operation

6. Connectedness

Resources Link to Each Other
Connectedness
- <?xml version=“1.0” encoding=“UTF-8” ?>
- <resource xmlns=http://example.com/ns/resource >
  - <content>…</content>
  - <nextResource href=http://example.com/resource/3/>
  - <prevResource href=http://example.com/resource/1/>
- </resource>
- <link rel=“alternate”type=“application/atom+xml” href=http://example.com/resource/2.atom/>
HATEOAS - Hypermedia as the Engine of Application State

7. Statelessness

HTTP Is Stateless - Every Request Happens in Isolation
State Machine
Resource State – Server-Side
Application State – Client-Side
Transferring Sate – Every HTTPrequest transfers state between the application and the requested resource
- Resource-> Application e.g. GET
- Resource<- Application e.g. PUT
Representation State Transfer

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