Tài liệu Introducing Databases doc

Introducing Databases
A database is an organized collection of information. A relational database is a
collection of related information that has been organized into structures known as tables.
Each table contains rows that are further organized into columns. You should already be
familiar with information being represented in the form of a table with columns. For
example, Table 2.1
shows the details of some products sold by the Northwind Company.
Table 2.1
lists the product ID, name, quantity per unit, and unit price for the first 10
products; this information comes from the Products table of the Northwind database.
Table 2.1: SOME ROWS FROM THE PRODUCTS TABLE
PRODUCT ID NAME QUANTITY PER UNIT Unit Price
1 Chai 10 boxes x 20 bags $18
2 Chang 24-12oz bottles $19
3 Aniseed Syrup 12-550ml bottles $10
4 Chef Anton's Cajun Seasoning 48-6oz jars $22
5 Chef Anton's Gumbo Mix 36 boxes $21.35
6 Grandma's Boysenberry Spread 12-8oz jars $25
7 Uncle Bob's Organic Dried Pears 12-1lb pkgs. $30
8 Northwoods Cranberry Sauce 12-12oz jars $40
9 Mishi Kobe Niku 18-500g pkgs. $97
10 Ikura 12-200ml jars $31
You can store the information in a database on paper in a filing cabinet or in electronic
format stored in the memory and file system of a computer. The system used to manage
the information in the database is the database management system. In the case of an
electronic database, the database management system is the software that manages the
information in the computer's memory and files. One example of such software is SQL
Server (this is the relational database management system, or RDBMS, used in this book).
Other examples of RDBMS software include Oracle and DB2.

Note You must be careful to differentiate between a database and a database management
system. A database is an organized collection of information, and a database
management system is the software that stores and provides the tools to manipulate
the stored information. This distinction is blurred these days, so the term database is
often used to refer to the software.
Another term you need to be familiar with is a database schema, which is a representation
of the structure of data, and includes the definition of the tables and columns that make
up the database.
In the next section
, you'll explore SQL Server.