1. Advanced Web-based Systems | Misbhauddin
Web Services
REST
Advanced Web-based Systems | Misbhauddin

2. Advanced Web-based Systems | Misbhauddin
Web Services
Web services are web application components that provide an interface to the applications and not users
Approaches
XML-RPC
SOAP
REST
Client / Server
Web Services
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3. Advanced Web-based Systems | Misbhauddin
Web Scalability Issue
The WorldWideWeb (W3) is a wide-area hypermedia information retrieval initiative aiming to give universal access to a large universe of documents.
- Tim Berners-Lee
The above was said about the web in 1991
Web began to grow exponentially since then
The “Universe of Documents” was expanding
The Web was growing too large, too fast, and it was heading toward collapse
It was unclear if the Web would scale to meet the increasing demand
Advanced Web-based Systems | Misbhauddin

4. Web Scalability - Solution
Roy Fielding got concerned by the Web Scalability Problem
Web’s scalability was governed by a set of key constraints
Uniformly satisfy all of the constraints - so that the Web could continue to expand
Advanced Web-based Systems | Misbhauddin

5. Advanced Web-based Systems | Misbhauddin
Constraints
The six constraints are:
Client-Server
Uniform Interface
Layered System
Cacheable
Stateless
Code on Demand (optional)
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6. Advanced Web-based Systems | Misbhauddin
Client-Server
Web is a client-server based system
Clients and Servers have distinct parts to play
They may be implemented and deployed independently
using any language or technology
Assume a disconnected system
Separation of Concern
But they should conform to Uniform Interface
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7. Advanced Web-based Systems | Misbhauddin
Uniform Interface
There is interaction between web components
Clients, Servers, Intermediaries
Depends on a uniform interface between them
If any of them move away from standards
Web Communication breaks down
Four sub-constraints - Simplifies and decouples the architecture
Identification of resources;
Manipulation of resources through representations;
Self-descriptive messages;
HATEOAS
Advanced Web-based Systems | Misbhauddin

8. Identification | Uniform Interface
Identification of Resources
Each web-based concept is known as a resource
It is addressed by a unique identifier – URI
Advanced Web-based Systems | Misbhauddin

9. Manipulation | Uniform Interface
Manipulation of Resources through Representations
Clients manipulate representation of resources
Same resource is represented in different way to different clients
A file can be sent as a HTML to a web browser and as a JSON to an application
Resources can be manipulated through representations without changing the actual resource
Advanced Web-based Systems | Misbhauddin

10. Self-Descriptive | Uniform Interface
Self-Descriptive Messages
Desired representation (or state) can be mentioned in the request message
Current state is mentioned in the response message
The resource state is included as a self-descriptive message
Advanced Web-based Systems | Misbhauddin

11. HATEOAS | Uniform Interface
Hypermedia As The Engine Of Application State
A resource’s state includes link to other resources
The presence or absence of a link is a part of the resource’s current state
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12. Advanced Web-based Systems | Misbhauddin
Layered System
Client cannot assume direct connection to the server
Software or hardware intermediaries between the server and the client – Gateways and Proxies
Also called network based intermediaries
Improves scalability
Network-based intermediaries are commonly used for
Enforcement of security
Response caching
Load balancing
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13. Advanced Web-based Systems | Misbhauddin
Cacheable| REST
Caching is one of web architecture’s most important constraints
Caching response data can help
Reduce client-perceived latency
Increase the overall availability and reliability of an application
Control a web server’s load
In other words, caching reduces the cost of the web
Cache can exist in any place in the path between the client and the server
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14. Advanced Web-based Systems | Misbhauddin
Stateless| REST
Web Server does not remember the state of its client applications
Each request contains enough context to process the message
Self-descriptive messages;
Any session state is kept on the client
Client manage the state – Server can service much larger clients
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15. Advanced Web-based Systems | Misbhauddin
Code on Demand| REST
Server can temporarily transfer executable code (scripts and plug-ins) to the client
Transfer logic to client - Client executes logic
Client must be able to understand and execute the code that it demands from the server
This is why it is Optional
For example
JavaScript
Java Applets
Flash
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16. Advanced Web-based Systems | Misbhauddin
REST
Representation State Transfer
Set of architectural principles – data transmitted over HTTP
Focus on design rules for stateless service
Each resource is represented using a unique URI
Representation of the resource is returned
With each representation, client can transfer state
All-in-all, it is an architectural style composed of all the six constraints
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17. Advanced Web-based Systems | Misbhauddin
RESTful Web Services
Request
Client
Web API
Web Service Backend
Response
Web API is the face of the Web Service
REST style is applied to the design of the API
The API is called REST API and the service becomes RESTful
The REST API consists of interlinked resources
The set of resources is known as the resource model
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18. Advanced Web-based Systems | Misbhauddin
URIs
REST APIs use Uniform Resource Identifiers (URIs) to address resources
Identify the things that you want to operate on – meaning RESOURCES
A web page is a type of resource
/professors
List of all professors at CCSIT
/professors/Misbhauddin
Identify professor named ‘Misbhauddin’
GET /professors/Misbhauddin HTTP/1.1
Host: kfu.edu.sa/ccsit
Resources are best thought
of as nouns
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19. Advanced Web-based Systems | Misbhauddin
Resource Archetypes
Document: A document resource is a singular concept similar to a database record.
A document may have child resources that represent its specific subordinate concepts.
docroot
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Resource Archetypes
Collection: A collection resource is a server-managed directory of resources.
Clients may propose new resources to be added to a collection
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21. Advanced Web-based Systems | Misbhauddin
Resource Archetypes
Store: A store is a client-managed resource repository.
A store resource lets an API client put resources in, get them back out, and decide when to delete them.
The example interaction above shows a user (with ID 1234) of a client program using a REST API to insert a document resource named brazil in his store of favorites
PUT /users/1234/favorites/brazil
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22. Advanced Web-based Systems | Misbhauddin
Resource Archetypes
Controller: Controller resources are like executable functions, with parameters and return values; inputs and outputs.
Controller names typically appear as the last segment in a URI path, with no child resources
POST /alerts/245743/resend
POST /alerts/245743/resend/resource
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23. Advanced Web-based Systems | Misbhauddin
URI Design
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24. Advanced Web-based Systems | Misbhauddin
Interactions
Used to manipulate a resource’s representation
Lets say we want to add a new professor
Two ways
OR ……
Use a specific URL
Use HTTP Verbs
/professors/add
Not RESTful
GET /professors/Misbhauddin HTTP/1.1
Host: kfu.edu.sa/ccsit
Advanced Web-based Systems | Misbhauddin

25. HTTP Verbs | Request Actions
HTTP verbs tell the server what to do with the data identified by the URL.
GET
used to get the representation of the resourse
PUT
used insert or update a resource
DELETE
used to delete a resource from the parent
POST
used to create a new resource in the collection or execute controller
HEAD
used to get the Headers of the response only
OPTIONS
used to get info about resource’s available interactions
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26. Advanced Web-based Systems | Misbhauddin
Request Message
> GET /greeting HTTP/1.1
> User-Agent: chrome /7.20.1
> Host: api.example.restapi.org
> Accept: */*
< HTTP/ OK
< Date: Sat, 20 Aug :02:40 GMT
< Server: Apache
< Expires: Sat, 20 Aug :03:40 GMT
< Cache-Control: max-age=60, must-revalidate
< ETag: text/html:hello world
< Content-Length: 130
< Last-Modified: Sat, 20 Aug :02:17 GMT
< Vary: Accept-Encoding
< Content-Type: text/html
<!doctype html><head><meta charset="utf-8"><title>Greeting</title></head>
<body><div id="greeting">Hello World!</div></body></html>
Request Headers
Response Message – Status Line
Response
Headers
Example
Response Body
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27. Advanced Web-based Systems | Misbhauddin
Representations
The HTTP client and HTTP server exchange information about resources identified by URIs
Typically resource is represented using JSON or XML
Example
Resource: person (Mohammed)
Service: contact information (GET)
Representation:
Name, address, phone number
JSON or XML format or VCard
Advanced Web-based Systems | Misbhauddin

28. Advanced Web-based Systems | Misbhauddin
SOAP vs. REST
SOAP
REST
Language, platform, and transport independent (REST requires use of HTTP)
Works well in distributed enterprise environments (REST assumes direct point-to-point communication)
Standardized
Provides significant pre-build extensibility in the form of the WS* standards
Built-in error handling
Automation when used with certain language products
No expensive tools require to interact with the Web service
Smaller learning curve
Efficient (SOAP uses XML for all messages, REST can use smaller message formats)
Fast (no extensive processing required)
Closer to other Web technologies in design philosophy
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29. Advanced Web-based Systems | Misbhauddin
Recommended Reading
For the REST architecture
REST API Design Rulebook
by Mark Masse
Publisher: O'Reilly Media, Inc.
Release Date: October 2011
Chapters 1, 2, and 3
Advanced Web-based Systems | Misbhauddin