Web services

Example: Your app posts updates to Twitter without leaving the app. Needs read-write access over network. Through API interface - calling methods on remote site. Needs authentication.

Example: Manufacturer automatically queries distributors for stock levels and other shared information. Done over network, but general public has no access to this information.

The name "Web" implies uses HTTP. But some services in fact do not.

• APIs in general
  • Web APIs (and here)
  • Web services

• programmableweb.com
  • API list

• Service-oriented architecture (SOA) is the general design principle.
• The service may be:
  1. Public or private.
  2. Paid or free.
  3. Authenticate or not. Even free service can need authenticate. e.g. Your own YouTube account.
  4. Between company and partner company only. e.g. Stock tracking service to/from supplier and customer.
  5. Between two divisions inside a company. A big feature of SOA thinking is to make one department's work usable by another department.

Service description

• Describing the service precisely and in detail is essential. Though some descriptions are more formal than others.
• Web Services Description Language (WSDL) (XML language for describing Web services)
• Web Application Description Language (WADL) (XML language for describing REST Web services)

Popular APIs

2017 survey of APIs shows REST dominant, SOAP still in use.

2019 graph showing growth in number of different web APIs.

REST v SOAP

• REST
  1. Allows any data format.
  2. It often uses JSON for fast parsing on client side. But this is not required. Other formats can be used.
  3. Simple to code and deploy. Easy for large numbers of developers to use.
  4. Can use https for security.
  5. Widely used for "open APIs" with large number of developers.

• SOAP
  1. Uses XML.
  2. Apart from being restricted to one format, XML often involves more overhead - more bytes of data, more parsing time.
  3. Higher learning curve for developers.
  4. SOAP has more advanced WS-Security for mission-critical security.
  5. Widely used in business.
     Note some APIs are business-to-business (or department-to-department within one company) and not known to public.

Future of APIs

• Alternatives to REST

• The future of API design: The orchestration layer by Daniel Jacobson, makes a few points:
  • Simple APIs like REST are good for a large number of unknown remote developers who need no install.
  • If small number of known client developers, more specialised solutions with install of specialised libraries/clients may be better.