Sommerville-Software-Engineering-10ed

18.2 ■ RESTful services 531
3. PUT is used to update the value of a resource.
4. DELETE is used to delete the resource.
All services, in some way, operate on data. For example, the service described in
Section 18.2 that returns the maximum and minimum temperatures for a location on
a given data uses a weather information database. SOAP-based services execute
actions on this database to return particular values from it. RESTful services
(Richardson and Ruby 2007) access the data directly.
When a RESTful approach is used, the data is exposed and is accessed using its
URL. RESTful services use http or https protocols, with the only allowed actions
being POST, GET, PUT, and DELETE. Therefore, the weather data for each place in
the database might be accessed using URLs such as:
http://weather-info-example.net/temperatures/boston
http://weather-info-example.net/temperatures/edinburgh
This would invoke the GET operation and return a list of maximum and minimum
temperatures. To request the temperatures for a specific date, a URL query can be used:
http://weather-info-example.net/temperatures/edinburgh?date=20140226
URL queries can also be used to disambiguate the request, given that there may
be several places in the world with the same name:
http://weather-info-example.net/temperatures/boston?date=20140226&country=
USA&state=“Mass”
An important difference between RESTful services and SOAP-based services is
that RESTful services are not exclusively XML-based. So, when a resource is
requested, created, or changed, the representation may be specified. This is important
for RESTful services because representations such as JSON (Javascript Object
Notation), as well as XML, may be used. These can be processed more efficiently
than XML-based notations, thus reducing the overhead involved in a service call.
Therefore, the above request for maximum and minimum temperatures for Boston
may return the following information:
{
“place”: “Boston”,
“country “USA”,
“state”: “Mass”,
“date”: “26 Feb 2014”,
“units”: “Fahrenheit”,
“max temp”: 41,
“min temp”: 29
}
The response to a GET request in a RESTful service may include URLs.
Therefore, if the response to a request is a set of resources, then the URL of each of