Databases Reference
In-Depth Information
Current development environments provide interface options, letting the
developer choose the option best suited to the database server. The database
designer/implementer may be asked to make recommendations, but not the final
decision.
11.1.3 Understanding Multitier Connectivity
As you move into a multitier environment, the difference is one of scale and dis-
tribution rather than basic functionality. Different functions are delegated to dif-
ferent specialized servers. Typically, the database server becomes more focused
on that single task.
Let's take a look at an example of this type of environment so you can see
something of the delegation involved between the servers. In this example, there
is a multi-tiered Web application; however this is not the only type of configu-
ration you might see. Most Web applications are multi-tier applications, but
multi-tiered applications are not necessarily Web applications.
Suppose that Good Reading Bookstores develops a Web site to sell books
to consumers online and that you are about to become one of its customers.
The browser software in your PC sends a message to Good Reading's Web
server and establishes a connection with it. The Web server sends your browser
Good Reading's home page which your browser displays. From here, you can
make requests of the application running on Good Reading's Web server. This
application sends commands to the relational DBMS on Good Reading's data-
base server, ordering it to perform requested operations and returning the
information to your browser. This continues with other requests as necessary.
Every time the database must be accessed, the application in the Web server
passes a command to the database server, which queries the database and
returns the result.
Figure 11-6 shows this process in some detail, introducing some of the spe-
cialized software involved. When your browser sends a message to the Web
server (and vice versa), the message follows the rules of the
Transmission Con-
trol Protocol/Internet Protocol (TCP/IP),
the protocol on which the Internet
and most other networks are based, and the
Hypertext Transfer Protocol
(HTTP),
which is an additional protocol layer supporting World Wide Web traf-
fic on the Internet.
There is a potential problem in that there can be different kinds of hardware
between the Web server and the database server, different kinds of application
software languages, different browsers on the client side, and a variety of different
kinds of data. These are tied together using specialized interfaces and specialized
software known as
middleware.
Because of the importance of connecting the
applications in the Web server with the databases in the database server, various
companies have developed specialized middleware with a variety of broad
features, capabilities, and connectivity options. Among the products of this type
