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You can create relationships between tables —That's where the “relational” in
relational database comes from. You can relate articles to authors, invoices to cus-
tomers, or even people to other people within the same table. The relational model
is very, very powerful.
Relational databases use a standard query language called SQL (Structured
Query Language) —Although some differences exist between database vendors, if
you know SQL you can work with just about any relational database.
Relational databases are popular —The basic technology behind relational data-
bases hasn't changed much in the past 20 years, and they are the foundation of
many business applications. What has changed is that now several relational data-
bases are freely available, providing powerful features once only associated with
the most expensive software targeted at large corporations. Relational databases are
so popular and common that using them for data storage for an application is often
an easy decision.
Relational databases are usually deployed as a service that is accessible over the network,
much like an HTTP server. The difference is that instead of using HTTP to communi-
cate, the database will use its own proprietary protocol. To communicate with a database,
you generally need some kind of client or library provided by the database vendor. PHP
has clients for most popular relational databases built in, so you can just use the func-
tions associated with your database and not install anything extra.
Most hosting providers that allow you to use PHP, CGI scripts, or some other scripting
environment also provide access to relational databases. You may have to fill out a spe-
cial form to have a database set up for you. After it's set up, your hosting provider will
give you the hostname of your database server and a username or password. You can use
that information to access the database, or in the case of packaged software, you can use
it to configure the software so that it can access the database.
After a relational database is installed, all the administrative tasks—from creating spe-
cific databases to creating and managing users—are accomplished using SQL. So to con-
figure a database for a particular application, you generally create a new user and
database for it to use and then run an installation script that creates all the tables that the
application needs and inserts the initial data into the database. You hosting provider will
often take care of creating the user and database, and you will run the installation script
that builds the initial database.
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