scheme :The components of a URL

第一部分是协议(或称为服务方式)。资源的访问方式？

 

A URL for HTTP (or HTTPS) is normally made up of three or four components: 

1. A scheme. The scheme identifies the protocol to be used to access the resource on the Internet. It can be HTTP (without SSL) or HTTPS (with SSL).
2. A host. The host name identifies the host that holds the resource. For example, www.example.com. A server provides services in the name of the host, but hosts and servers do not have a one-to-one mapping. Refer to Host names.

   Host names can also be followed by a port number. Refer to Port numbers. Well-known port numbers for a service are normally omitted from the URL. Most servers use the well-known port numbers for HTTP and HTTPS , so most HTTP URLs omit the port number.

3. A path. The path identifies the specific resource in the host that the web client wants to access. For example, /software/htp/cics/index.html. 
4. A query string. If a query string is used, it follows the path component, and provides a string of information that the resource can use for some purpose (for example, as parameters for a search or as data to be processed). The query string is usually a string of name and value pairs; for example, term=bluebird. Name and value pairs are separated from each other by an ampersand (&); for example, term=bluebird&source=browser-search.

The scheme and host components of a URL are not defined as case-sensitive, but the path and query string are case-sensitive. Typically, the whole URL is specified in lowercase.

The components of the URL are combined and delimited as follows:

scheme://host:port/path?query

• The scheme is followed by a colon and two forward slashes.
• If a port number is specified, that number follows the host name, separated by a colon.
• The path name begins with a single forward slash.
• If a query string is specified, it is preceded by a question mark. 

Figure 1. Syntax of an HTTP URL

 the scheme
 ┌───┐
 https://www.google.com/
 └───┘
 the specific protocol