Web Services Are Not Web Pages

Across the web, users make extensive use of sites that perform specific tasks. People book their travel, for example, at Travelocity, buy books at Amazon, perform online banking at Bank of America, and order pizza at Domino’s. These sites offer services to the user, but the sites are webpages, not web services. A web service is program code that resides on the web and performs a specific task that other programs, not people, use. Examples of tasks that a web service might perform include the following:

• Return the weather conditions for a specific zip code

• Return real-time traffic conditions for a road or highway

• Return a stock price for a specific company

• Return driving directions to a specific location

• Return the country associated with an IP address

• And much more

Programmers use web services within the programs they create to perform specific processing. To use a web service, a program exchanges messages across the Internet with the web service that resides on a remote server. The program may pass parameter values to the service, such as a stock symbol of the company for which the program wants the stock price or the zip code of the area for which the program wants weather conditions. When a program calls a web service, the program will normally send its message to the web service via a function call and then wait, as shown in FIGURE 11.2, for the web service to return its result.

Programmers often refer to web services as microservices or APIs, which stands for “application program interface (API).” When you hear the term “API”, think “web service.”