In order to create web sites and web applications, it's important to understand how web applications work and how the Internet works. The internet is a huge entitiy - a network of computers all over the world, or a network of networks. The primary architecture of these networks is the client-server network. This network architecture allows us to connect our own individual machines to the millions and billions of machines that make up the networks of the Internet.
When people refer to a client-server model, or client-server architecture, they're referring to a design of networked machines with the main files, programs, and services on a single computer called a server. Those resources can be shared among other machines on the network, which are called clients. The Internet is an example of client-server architecture: Many resources are stored on servers, and we can all use our own client machines to access those resources. The Internet is a huge, complex map of clients and servers, all connected together, allowing the world to share an infinite supply of electronic resources.
A server is also the software that manages the server's connections and access, and "serves" up requests for resources that are made by client machines. The machine that the server software resides on can be any computer that's powerful enough to run the server and perform the tasks the server needs to perform.
There are different types of servers: web servers host web sites, database servers host databases full of data, file servers host files that users can upload and download, game servers host games that users can connect to and play with each other, a print server hosts printing services that manage print jobs and a network of printers, and there are many others.
A client can refer to a machine, or it can refer to an application. Right now your computer is connected to a local network, and is therefore a client machine. If you're also using your smart phone or tablet, you're probably also connected to a local network or your carrier's network (your phone service provider's network), so they're also clients.
Additionally, any software program that allows your client machine to request information from a server, receives the returned results, and then presents those results in a human-readable format is also a client (client software, to be more precise). Your web browser is a client, for example: You use the web browser to request web pages, which are then rendered in the browser window for you to see and interact with. If you run an email program on your computer such as Thunderbird or Outlook, you're using an email client. An FTP client is a piece of software (such as WS-FTP, Core FTP, AnyClient, FileZilla, etc) that allows you to connect to a server so you can upload and download files. Think of any program on your computer, smart phone, tablet or other device that allows you to access shared resources on a server out there somewhere on the Internet: that's a client program!
How does client-server architecture apply to a course in web development? Some of the technologies used to develop these applications are server-side technologies, and others are client-side technologies. Server-side technologies, such as PHP, Perl, and MySQL perform their processing on the server. Client-side technologies, such as HTML, CSS, and JavaScript perform their processing on the client.
Examples of technologies used in web development:
The data flow in a client-server network can be complex for interactive web pages and for web applications. However, in these tutorials we start by learning the fundamentals, which means we will be creating static web pages (web pages with no interactivity, whose content doesn't change unless the programmer changes it and uploads a new version). Static pages have a very simple data flow on a web server:
In later tutorials, you'll learn how to use technologies such as CSS, JavaScript, and PHP to create interactive and even dynamic pages (pages whose content can change, or pages whose content is read from sources like a database or JSON (JavaScript Object Notation)).
The Request/Response Model is how clients and servers communicate with each other. The client sends requests to the server, the server then processes and fulfills these requests, and then sends the response back to the client.
For example, say you visit the page Wendi's Cats:
If the request involves server-side processing, then the process is a bit more complicated, as there are more steps to be completed. For example, what happens when you log into SLATE? You'll learn more about this process in the Web Programming course in term 2.