Web service (WS)
- A service offered by an electronic device to another electronic device, communicating with each other via the World Wide Web, or
- A Web service is a server running on a computer device, listening for requests at a particular port over a network, serving web documents (HTML, JSON, XML, Images), and creating web applications services, which serve in solving specific domain problems over the web (www, internet, HTTP)
In a Web service a Web technology such as HTTP — originally designed for human-to-machine communication — is used for transferring machine-readable file formats such as XML and JSON.
In practice, a Web service commonly provides an object-oriented Web-based interface to a database server, utilized for example by another Web server, or by a mobile app, that provides a user interface to the end user. Many organizations that provide data in formatted HTML pages will also provide that data on their server as XML or JSON, often through a Web service to allow syndication, for example, Wikipedia's Export. Another application offered to the end user may be a mashup, where a Web server consumes several Web services at different machines and compiles the content into one user interface.
The term "Web service" describes a standardized way of integrating Web-based applications using the XML, SOAP, WSDL and UDDI open standards over an Internet Protocol backbone. XML is the data format used to contain the data and provide metadata around it, SOAP is used to transfer the data, WSDL is used for describing the services available and UDDI lists what services are available.
A Web service is a method of communication between two electronic devices over a network. It is a software function provided at a network address over the Web with the service always on as in the concept of utility computing.
Many organizations use multiple software systems for management. Different software systems often need to exchange data with each other, and a Web service is a method of communication that allows two software systems to exchange this data over the Internet. The software system that requests data is called a service requester, whereas the software system that would process the request and provide the data is called a service provider.
Different software may use different programming languages, and hence there is a need for a method of data exchange that doesn't depend upon a particular programming language. Most types of software can, however, interpret XML tags. Thus, Web services can use XML files for data exchange.
Rules for communication between different systems need to be defined, such as:
- How one system can request data from another system.
- Which specific parameters are needed in the data request.
- What would be the structure of the data produced. (Normally, data is exchanged in XML files, and the structure of the XML file is validated against an .xsd file.)
- What error messages to display when a certain rule for communication is not observed, to make troubleshooting easier.
All of these rules for communication are defined in a file called WSDL (Web Services Description Language), which has a
.wsdl extension.
Application Programming Interface (API)
API is an interface or communication protocol between a client and a server intended to simplify the building of client-side software. It has been described as a “contract” between the client and the server, such that if the client makes a request in a specific format, it will always get a response in a specific format or initiate a defined action.
An API may be for a web-based system, operating system, database system, computer hardware, or software library.
An API specification can take many forms, but often includes specifications for routines, data structures, object classes, variables, or remote calls.POSIX, Windows API and ASPI are examples of different forms of APIs. Documentation for the API usually is provided to facilitate usage and implementation.
Popular API Examples
ProgrammableWeb, a site that tracks more than 15,500 APIs, lists Google Maps, Twitter, YouTube, Flickr and Amazon Product Advertising as some of the the most popular APIs. The following list contains several examples of popular APIs:
1. Google Maps API: Google Maps APIs lets developers embed Google Maps on webpages using a JavaScript or Flash interface. The Google Maps API is designed to work on mobile devices and desktop browsers.
2. YouTube APIs: YouTube API: Google's APIs lets developers integrate YouTube videos and functionality into websites or applications. YouTube APIs include the YouTube Analytics API, YouTube Data API, YouTube Live Streaming API, YouTube Player APIs and others.
3. Flickr API: The Flickr API is used by developers to access the Flick photo sharing community data. The Flickr API consists of a set of callable methods, and some API endpoints.
4. Twitter APIs: Twitter offers two APIs. The REST API allows developers to access core Twitter data and the Search API provides methods for developers to interact with Twitter Search and trends data.
5. Amazon Product Advertising API: Amazon's Product Advertising API gives developers access to Amazon's product selection and discovery functionality to advertise Amazon products to monetize a website.
Ref: Wikipedia.com
Ref: Webopedia.com
API vs Web Service
API and Web service serve as a means of communication. The only difference is that a Web service facilitates interaction between two machines over a network.
An API acts as an interface between two different applications so that they can communicate with each other. An API is a method by which the third-party vendors can write programs that interface easily with other programs.
A Web service is designed to have an interface that is depicted in a machine-processable format usually specified in Web Service Description Language (WSDL). Typically, “HTTP” is the most commonly used protocol for communication. Web service also uses SOAP, REST, and XML-RPC as a means of communication.
API may use any means of communication to initiate interaction between applications. For example, the system calls are invoked using interrupts by the Linux kernel API. An API exactly defines the methods for one software program to interact with the other. When this action involves sending data over a network, Web services come into the picture. An API generally involves calling functions from within a software program.
In case of Web applications, the API used is web based. Desktop applications such as spreadsheets and word documents use VBA and COM-based APIs which don’t involve Web service. A server application such as Joomla may use a PHP-based API present within the server which doesn’t require Web service.
A Web service is merely an API wrapped in HTTP. An API doesn’t always need to be web based. An API consists of a complete set of rules and specifications for a software program to follow in order to facilitate interaction. A Web service might not contain a complete set of specifications and sometimes might not be able to perform all the tasks that may be possible from a complete API.
The APIs can be exposed in a number of ways which include: COM objects, DLL and .H files in C/C++ programming language, JAR files or RMI in Java, XML over HTTP, JSON over HTTP, etc. The method used by Web service to expose the API is strictly through a network.
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