2. URLs and Resources

- Uniform resource locators are the standardized names for the Internet's resources.

 

- The future of URLs, including uniform resource names (URNs) - a framework to support objects that move from place to place while retaining stable names.

 

- URLs actually are a subset of a more general class of resource identifier called a uniform resource identifier, or URI

 

- URLs identifty resources by describing where resources are located, whereas URNs identify resources by name, regardless of where they currently reside.

 

- Scheme, Server location, Resource path (scheme, host, path)

 

- Before the Web and URLs, people relied on a rag-tag assortment of applications to access data distributed throughout the Net.

 

- Using URLs, these applications are able to access many resources in a uniform way, through one interface.

 

- The host component identifies the host machine on the Internet that has access to the resource.

 

- The query component of the URL is passed along to a gateway resource,

 

- To allow referencing of parts or fragments of a resource, URLs support a frag component to identify pieces within a resouurce

 

- Because HTTP servers generally deal only with entire objects, not with fragments of objects, clients don't pass fragments along to servers. After your browser gets the entire resource from the server, it then uses the gragment to display the part of the resource in which you are interested.

 

- They were also designed to uniformly name all theresources on the Internet, which means that they will be transmitted throuugh variouus protocols. Because all of these protocols have different mechanisms for transmitting their data, it was important for URLs to be designed so that they could be transmitted safely through any Internet protocol.

 

* Portable : When used to describe software, portable means that the software has the ability to run on a variety of computers.

 

- The encoding simply represents the unsafe character by an "escape" notation, consisting of a percent sign(%) followed by two hexadecimal digits

 

- For some transport protocols this is not an issue, but it is still unwise for application developers not to encode unsafe characters.

 

- Once all the unsafe characters have been encoded, the URL is in a canonical form that  can be shared  between applications; there is no need to worry about the other application getting confused by any of the character's special meanings.

 

 

- The only difference is that the https scheme uses Netscape's Secure Sockets Layer (SSL), which provides end-to-end encryption of HTTP connections. Its syntax is identical to that of HTTP, with a default port of 443.