Client-Server Model

In order to build database-backed web applications, we first need to understand how servers, clients, and databases interact.

A major part of this is the client-server model , so let's look at that first. The basic idea is very simple, and looks something like this:

A server is a centralized program that communicates over a network (such as the Internet) to serve clients .

And a client is a program (like the web browser on your computer) that can request data from a server.

When you go to a web page in your browser, your browser (the client) makes a request to the server—which then returns the data for that page.

Adding databases to the model

So that's the basic client-server model. But when you add in databases, this creates a little more complexity.

In this next video, we'll review the basic model and then see how databases fit into things.

In summary, relational database systems follow a client-server model :

Servers, Clients, Hosts

• In a Client-Server Model, a server serves many clients .
• Servers and clients are programs that run on hosts .
• Hosts are computers connected over a network (like the internet!).

Requests and Responses

• A client sends a request to the server
• The server's job is to fulfill the request with a response it sends back to the client.
• Requests and responses are served via a communication protocol , which sets up the expectations and rules for how the communication occurs between servers and clients.

Relational Database Clients

• A database client is any program that sends requests to a database
• In some cases, the database client is a web server! When your browser makes a request, the web server acts as a server (fulfilling that request), but when the web server requests data from the database, it is acting as a client to that database—and the database is the server (because it is fulfilling the request).

Don't let this confuse you. Basically, we call things clients when they are making a request and servers when they are fulfilling a request. Since a web server can do both, it sometimes acts as a server and sometimes acts as a client.

QUIZ QUESTION: :

Let's review the basic vocabulary we've covered. See if you can match each term with the correct description.

ANSWER CHOICES:

QUIZ QUESTION: :

See if you can fill in the blanks in the sentences below.

ANSWER CHOICES: