A web API is the application programming interface (API) for both the web server and web browser."Its main purpose is to allow application developers to call a set of routines functions without considering why its underlying source code, or understand the details of its internal working mechanisms. ASP.NET Web API is to help HTTP services reach different clients and it is an ideal platform for building RESTful applications on the .NET Framework.
- 1 Server-side
- 2 Client-side
- 3 Web API Services
- 4 Differences between Web API and Web Services
- 5 Main Function of API
- 6 Other forms of API
- 7 API Modeling Languages
- 8 See also
- 9 References
- 10 Further reading
A server-side web API is a programmatic interface to a defined request-response message system, typically expressed in JSON or XML, which is exposed via the web—most commonly by means of an HTTP-based web server. Mashups are web applications which combine the use of multiple such web APIs. Webhooks are server-side web APIs that take as input a URI that is designed to be used like a remote named pipe or a type of callback such that the server acts as a client to dereference the provided URI and trigger an event on another server which handles this event thus providing a type of peer-to-peer IPC.
While "web API" in this context is sometimes considered a synonym for web service, Web 2.0 web applications have moved away from SOAP-based web services towards more cohesive collections of RESTful web resources. These RESTful web APIs are accessible via standard HTTP methods by a variety of HTTP clients including browsers and mobile devices.
Google created their Native Client architecture which is designed to help replace insecure native plug-ins with secure native sandboxed extensions and applications. They have also made this portable by employing a modified LLVM AOT compiler.
Web API Services
Information Services provide massive specific information, including geographical data like Google Maps API , like the Amazon E-Commerce , Product Data Amazon historcal Pricing Services and the latest release of Yahoo. These services have in common is that they are available
Storage services concern abstraction and virtualization storage. Leader in this area is amazon s3. For developers, S3 provides an extremely streamlined abstract like a hash table like the API, allowing you to easily access information.
message service middleware in the traditional sense is similar in concept. Because of the complexity of the technical and commercial, they have not been large-scale development. Short term visible web-based communications services is Amazon Simple Queue Service. This service enables any application between security and scalable queue-based communication more convenient. 
there is no one that can be accessed by the general computing services API black box, but there are a number of technical points to this direction.
Because the search base and dominance in the field of web search services are a key part of the new web infrastructure. An example is Alexa search platform, which led to a series of challenges designed vertical position google search engine. Quite interesting from a technical point of view, alexa search platform more performance for a computing services, but limitations in the search field only. 
Differences between Web API and Web Services
Web service is basically a standard communication between different electronic devices. 
Web API is one of the Web services based on HTTP however it is undefined, which means everyone can provide their description just by PDF and it is not standard. Uses HTTP isnot a transport protocol. 
Main Function of API
The main function of the Web API 
•Supports Http verb (GET, POST, PUT, DELETE) the CRUD (create, retrieve, update, delete) operations
•Express different meanings by different http action, so do not need to expose multiple API to support these basic operations.
•Request reply to express different meanings through Http Status Code, and the client can Accept header to negotiate with the server format, for example you want the server to return JSON format or XML format
•Request Reply format support JSON, XML, and can be extended to add other formats.
•native support OData.
•Support Self-host or IIS host.
•Most MVC support functions, such as Routing https://en.wikipedia.org/wiki/Routing/ Controller Controller/ Action Result / Filter / Model Builder / IOC Container / Dependency Injection Dependency_injection
Other forms of API
API is divided into (Windows, Linux, Unix and other systems) system-level API, and non-operating system-level custom API.
Object-oriented language APIApplication_programming_interface
Object-oriented is a programming thinking, which combines "Properties" and "conduct", closer to naural concept of human. The basic idea of Object-oriented is variable objects and operations bundled package, suppored by a progamming language and thus have its own package characteristics, such as SmalltalkSmalltalk, JavaJava, .net.net.
Windows API is using Windows to show data through internet and start the communication.
API Modeling Languages
A number of Modeling languages have been proposed for describing practical Web APIs including:
- Wasson, Mike. "Microsoft ASP.NET". Microsoft ASP.NET. Retrieved 20 January 2014.
- "Mashup Dashboard". ProgrammableWeb.com. 2009.
- Benslimane, D.; Dustdar, S.; Sheth, A. (2008). "Services Mashups: The New Generation of Web Applications". IEEE Internet Computing 10 (5): 13–15. doi:10.1109/MIC.2008.110.
- WebMonkey News
- Mozilla WebAPI Wiki
- Gibilisco, Stan. [ "google maps"]. whatls.com. Retrieved February 2013.
- .O, admin. [ "Amazon E-Commerce"]. awsbook. Retrieved 25 October 2014.
- Shanahan, Francis (3 January 2007). [ Product Data Amazon historcal Pricing Services] (1 ed.). wrox. ISBN 978-0470097779. Retrieved 25 October 2014.
- Rouse, Margaret. [ "Amazon S3"]. whatls. Retrieved 25 October 2014.
- Singh, Niraj. [ "Amazon Simple Queue Service using java"]. jave code greeks. Retrieved 25 June 2013.
- Nguyen, Michael. [ "Alexa Web Search Platform"]. SEJ. Retrieved 13 December 2005.
- McIver, Aaron. "web service". programmers. Retrieved 21 January 2011.
- D., Ranjan. [ "web API"]. code project. Retrieved 11 March 2013.
- .LG, Huo. [【http://www.uml.org.cn/net/201402285.asp】 "main function of API"]. uml.org.cn. Retrieved 28 February 2014.
- Steane, Andrew. "Windonws API". Quick introduction to Windows API. Retrieved 2007.
- Fisher, Tim. [ "Direct X"]. about technology. Retrieved 25 October 2014.
- Jacobson, Daniel; Woods, Dan; Brail, Greg (November 2011). APIs a strategy guide. Sebastopol, Calif: O'Reilly Media. ISBN 978-1-4493-0892-6.
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