REST and Resource Oriented Architecture - okcDG March 2008

REST
and Resource Oriented Architecture
okcDG
March 2008
Ryan Hoegg
Valtech Technologies

REST, ROA, and Web Services
Architectural style of the WWW
One way to build RESTful
web services
Not very well defined
REST:
ROA:
Web Services:

So what is “Web Services”?
...hem hem haw hem haw...
What they said
<shrug/> Here's some software.
They're great! Buy our tools!
W3C:
Wikipedia:
Apache:
Microsoft:

So what is “Web Services”??
Software services deployed on the WWW
intended for use by other software components

What is REST?
Architectural style for distributed hypermedia systems
Behind the architecture of the WWW
Described in “Architectural Styles and the Design of
Network-based Software Architectures” by Roy T.
Fielding

Software Architecture
A set of rules about the components, connectors,
and data in a software system intended to induce
some desired properties.
“...A software architecture is an abstraction of the run-time
elements of a software system during some phase of its
operation.”
--Roy T. Fielding

Architectural Style
“a set of rules that an architecture should
conform to”
-- from the RestWiki
“...a coordinated set of architectural constraints that restricts
the roles/features of architectural elements and the allowed
relationships among those elements within any architecture that
conforms to that style.”
-- Roy T. Fielding

Architectural Constraints
Addressable Resources
Statelessness
Connectedness
Uniform Interface

Resource?
Any information or concept that can be named.
The key abstraction of information in REST

Representation
The information about a resource that is
transmitted across the network.

Addressability
A resource identifier should represent only one
resource.

Statelessness
The server never stores any application state.
Each request can be considered in isolation.

“Connectedness”
The server includes levers of state in the
representations it sends to the client.

Uniform Interface
Resources share interface characteristics.
For example: methods, identifiers, data types

What does it buy me?
Large surface area
Scalable and Reliable
Easy to use and Robust
Transparent and Reliable
Addressable =
Stateless =
Connected =
Uniform =

Where REST came from
CERN – ENQUIRE project
MOMSpider and libwww-perl
mailing list for NCSA httpd becomes
the Apache HTTPD Project
REST guides the architecture of the
WWW, and the WWW serves as a
testbed for the ideas behind REST
1990-1992:
1993-1994:
1994-1995:
1995-now:

REST on the Web
URI
HTTP
Hypermedia

URI
Uniform Resource Identifier
Provides addressability of resources
e.g. http://okcpro.net/Events/MeetingsEvents/tabid/60/Default.aspx

Hypermedia?
Hypertext is text with links and forms.
Hypermedia expands this to include other
representations such as SVG.

HTTP
GET /Events/MeetingsEvents/tabid/60/Default.aspx
HTTP/1.1
Host: okcpro.net
HTTP/1.1 200 OK
Date: Mon, 10 Mar 2008 05:10:43 GMT
...
Content-Type: text/html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 ...
<html lang="en-US">
<head>
...
<title>Meetings and Events</title>...

HTTP Methods
Retrieve a resource
Retrieve resource metadata
Determine the methods supported by
a resource
Create or update a resource
Destroy a resource
Create a new subordinate resource
GET
HEAD
OPTIONS
PUT
DELETE
POST

Safety
A safe request does not change resource state

Idempotence
An idempotent request has the same effect if it
succeeds once or more than once

HTTP Response Codes
A set of standardized codes that describe the
outcome of an HTTP request.
100-199: Informational
200-299: Success
300-399: Redirection
400-499: Client error
500-599: Server error

HTTP Headers
Metadata about an HTTP request or response.
Some headers are control metadata, while others
are resource metadata.

Resource Oriented Architecture
“...a set of concrete rules for building web services that really
will be RESTful”
--Richardson and Ruby, “RESTful Web Services”

Method information:
What should the service do in response to this
request?
This is the HTTP method.

Scoping information:
On what data should the service operate?
This belongs in the URI.

ROA Oversimplified
1. Figure out the data set
2. Split the data into resources
For each kind of resource:
3. Name the resources with URIs
4. Expose a subset of the uniform interface
5. Design the representation(s) accepted from the client
6. Design the representation(s) served to the client
7. Integrate this resource into the others, using links and forms
8. What's supposed to happen?
9. What might go wrong?
Adapted from “RESTful Web Services”, by Richardson and Ruby

http://www.decentpizza.com/
A simple pizza delivery web service

Cool domain name huh?

There's a squatter in Ohio who thought so.

Some User Stories
Menu
Current Specials
Place Order
Check Order Status
Cancel Order

1. Figure out the data set
a menu of pizzas, sides, and toppings which have a
photo, a price, and a description
a special has a discounted price for one or more menu
items, and will expire.
an order has a creation time, a total price, a delivery
address, a status, and one or more menu items

2. Split the data set into resources
a menu
a pizza, identified by name
a side, identified by name
the list of available pizza toppings
a topping, identified by name
the list of current specials
a special
an order

3. Name the resources with URIs
the menu: http://www.decentpizza.com/menu
a pizza: http://www.decentpizza.com/menu/pizza/{name}
a side: http://www.decentpizza.com/menu/side/{name}
the list of toppings:
http://www.decentpizza.com/menu/toppings
a topping: http://www.decentpizza.com/menu/topping/
{name}
the list of current specials:
http://www.decentpizza.com/menu/specials
a special: http://www.decentpizza.com/menu/special/
{id}
an order: http://www.decentpizza.com/orders/{id}

4. Expose a subset of the uniform interface
For the menu and below: GET, HEAD, and OPTIONS
To place an order: POST
http://www.decentpizza.com/orders
To check order status: GET
http://www.decentpizza.com/orders/{id}
To cancel an order: DELETE
http://www.decentpizza.com/orders/{id}

5. Design the representation(s) accepted
from the client
Placing an order:

6. Design the representation(s) served to
the client
The menu:

6. Design the representation(s) served to
the client
An order:

7. Integrate this resource with other
resources using links and forms
When the client GETs an order, it includes a form that
describes how to cancel it:

8. What's supposed to happen?
For the menu and below: GET, HEAD, and OPTIONS
Response Code: 200 (OK)
POST http://www.decentpizza.com/orders :
Response Code: 201 (Created)
Location: http://www.decentpizza.com/orders/{new id}
GET http://www.decentpizza.com/orders/{id}:
DELETE http://www.decentpizza.com/orders/{id}:

The client may try to access a menu item or
special that doesn't exist, like
/menu/drinks/margarita
404 (“Not Found”)

The client might try to cancel an order that's
already been cancelled
404 (“Not Found”)

The client might POST an order that my service
doesn't understand
400 (“Bad Request”)

My ordering back end might be down
500 (“Internal Server Error”)

Where to learn more
The RestWiki
Roy T. Fielding's dissertation
RESTful Web Services (book)
The World Wide Web (surprised?)

REST and Resource Oriented Architecture - okcDG March 2008

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