APIs - Application Programming Interfaces

APIs What they are and why we use them

API Defined
Application Programming Interface
A way to use data or functionality written by a third party
Data / Functionality Abstraction
Often platform agnostic, nowadays very often web related / enabled
Different from
Software Library
Software Development Kit (SDK)

The I is for Interface
The Interface abstracts data / functionality.
The Interface can take many different forms
Libraries written for specific platforms
Example: DirectX for Windows, C++, C#
Example: Facebook has a PHP Library
Web interface
A whole 'nother beast
Data Formats: XML, YAML, JSON, SOAP, string, etc.
Transmission Formats: HTTP, HTTPS
Platform Formats: REST, Web Services, XML-RPC

Benefits of APIs
Web APIs
On the Web!
Put your data on highly trafficked sites
Access and store data in a central location
Not reinvent the wheel
Extend functionality
Non-Web APIs
Gain access to application functionality (Office)
Gain access to hardware
Not many apps provide an API nowadays, but more of a plugin system (Firefox, Google Desktop, Apple Widgets).
Control Robots.

Problems!!
APIs change
Salesforce.com guarantees 3 years of support
Complex
Google APIs are very complex
THINK API is easy to implement, very difficult to use
Documentation
THINK API
Authentication
Most APIs require a user or API key or both
Bugs
All software has bugs, APIs are no different
Error Messages
Some error messages are no help
HTTP Status codes in REST can mean different things

Example Uses of APIs
GeoCoder.us uses the most basic of interfaces
http://geocoder.us/service/csv?address=11045+Queens+Blvd,+Forest+Hills+NY+11375
Returns a CSV string
40.719546,-73.839686,11045 Queens Blvd,New York,NY,11375
Basecamp uses a complex interface
Data formatted as XML
REST based
https://delphicsage.basecamphq.com/projects/3804405/posts/26028930.xml

Example Uses Continued
THINK Subscription - SOAP through Web Services.
Twitter - XML or JSON through REST
Flickr - REST, XML-RPC or SOAP.
Salesforce.com - SOAP through Web Services
Amazon - SOAP through Web Services
YouTube - REST and ATOM with extensions.

What are all these protocols?
Web Services
WSDL (wizz-dull)
XML response data (.NET WS can return JSON too).
Pros: Generate code, development tools (Axis, .NET System.Web.Services, wsdl.exe)
Cons: Difficult to write code against if it's not generated. Heavy weight with strict type checking and XSD validation.
REST ( Representational State Transfer)
A representation of a resource is typically a document that captures the current or intended state of a resource.
Does not specify anything about the format of the data
Requests are made to URL
No definition language, no code generation in most cases
Pros: Less strict, less bulk, very straightforward, makes sense.
Cons: Less strict, all code must be written if no libraries from API provider. (Flickr provides many), some REST APIs mix important data in XML, HTTP Headers, HTTP Status codes.
XML-RPC
On its way out...

Example Application using APIs
Problem: You bought a digital camera, but it does not have a geocoding attachment. You also want to group images taken in the same general location together into albums on Flickr, and send a tweet out with a tinyURL link to the album.
Materials You Have:
Digital Camera
Blackberry or other GPS enabled device (GPS logger)
Internet connection
APIs required
????????
Discuss
How do I make it?
????????
Discuss

Another Application
Problem: You are unorganized and forget things immediately.
Materials:
Internet connection
Phone with Keyboard
Computer
APIs required
???????
Discuss
How do I make it?
???????
Discuss

You might be an API if...
Subjective...
Many things can be considered an API, even if the author did not intend for it to be called that.
Any SDK (software development kit) is probably a collection of APIs (like iPhone, Java, .NET SDK).
You make some complex task simple....
You make some inaccessible data accessible.....
You make accessing hardware simple (USB API, Network stack, OpenGL, OpenAL, etc)....
If you are accessing an external system without hacking, you're probably using an API.

You are definitely NOT an API if...
Code is written to run on you (Platform)
You are an application.
You're hardware.
You're data.
^^^ These are all things that an API would be written for!

Questions?

APIs - Application Programming Interfaces

by Jason Connell on Oct 14, 2009

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