In this article we will talk about URI, URN, and URL, and in previous article we already discussed about Content Security Appliances.

REST is an architectural style for designing web service applications. It refers to a style of web architecture that has many underlying characteristics and governs the behavior of clients and servers. Simply stated, a REST API is an API that works on top of the HTTP protocol. It defines a set of functions developers can use to perform requests and receive responses via HTTP protocol such as GET and POST.

Conforming to the constraints of the REST architecture is generally referred to as being “RESTful”. An API can be considered “RESTful” if it has the following features:

  • Client-Server – The client handles the front end and the server handles the back end. Either can be replaced independently of the other.
  • Stateless – No client data is stored on the server between requests. The session state is stored on the client.
  • Cacheable – Clients can cache responses to improve performance.


Web resources and web services such as RESTful APIs are identified using a URI. A URI is a string of characters that identifies a specific network resource. As shown in the figure, a URI has two specializations:

  • Uniform Resource Name (URN) – identifies only the namespace of the resource (web page, document, image, etc.) without reference to the protocol.
  • Uniform Resource Locator (URL) – defines the network location of a specific resource on the network. HTTP or HTTPS URLs are typically used with web browsers. Other protocols such as FTP, SFTP, SSH, and others can use a URL. A URL using SFTP might look like: sftp://sftp.example.com.

These are the parts of a URI, as shown in the figure:

  • Protocol/scheme – HTTPS or other protocols such as FTP, SFTP, mailto, and NNTP
  • Hostname – www.example.com
  • Path and file name – /author/book.html
  • Fragment – #page155

The figure depicts the parts of a Uniform Resource Identifier (URI). The figure displays the URI https://www.example.com/author/book.html#page155. The URL portion of the URI is: https://www.example.com/author/book.html. The URN portion is: www.example.com/author/book.html. The fragment is: #page155.

Parts of a URI

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