Review client-server architecture
Much of the Internet is based on the client-server model. In this model, user devices communicate via a network with centrally located servers to get the data they need, instead of communicating with each other. End user devices such as laptops, smartphones, and desktop computers are considered to be clients of the servers, as if they were customers obtaining services from a company. Client devices send requests to the servers for web pages or applications, and the servers serve up responses.
The client-server model is used because servers are typically more powerful and more reliable than user devices. They also are constantly maintained and kept in controlled environments to make sure they're always on and available; although individual servers may go down, there are usually other servers backing them up. Meanwhile, users can turn their devices on and off, or lose or break their devices, and it should not impact Internet service for other users.
Servers can serve multiple client devices at once, and each client device sends requests to multiple servers in the course of accessing and browsing the Internet.
URL
URL stands for Uniform Resource Locator. A URL is nothing more than the address of a given unique resource on the Web. In theory, each valid URL points to a unique resource. Such resources can be an HTML page, a CSS document, an image, etc. In practice, there are some exceptions, the most common being a URL pointing to a resource that no longer exists or that has moved. As the resource represented by the URL and the URL itself are handled by the Web server, it is up to the owner of the web server to carefully manage that resource and its associated URL.
A URL is composed of different parts, some mandatory and others optional. The most important parts are highlighted on the URL below (details are provided in the following sections):
The first part of the URL is the scheme, which indicates the protocol that the browser must use to request the resource (a protocol is a set method for exchanging or transferring data around a computer network). Usually for websites the protocol is HTTPS or HTTP (its unsecured version).
The domain indicates which Web server is being requested. Usually this is a domain name, but an IP address may also be used (but this is rare as it is much less convenient).
The port indicates the technical "gate" used to access the resources on the web server. It is usually omitted if the web server uses the standard ports of the HTTP protocol (80 for HTTP and 443 for HTTPS) to grant access to its resources. Otherwise it is mandatory.
/path/to/myfile.htmlis the path to the resource on the Web server.?key1=value1&key2=value2are extra parameters provided to the Web server. Those parameters are a list of key/value pairs separated with the&symbol. The Web server can use those parameters to do extra stuff before returning the resource.#SomewhereInTheDocumentis an anchor to another part of the resource itself. An anchor represents a sort of "bookmark" inside the resource, giving the browser the directions to show the content located at that "bookmarked" spot.
References
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