A relational database consists of a collection of tables where each table has 1) a definition part and 2) a content part.
The heading part consists of the table name and the column names.
Once you have created entities representing the business objects you want to represent in your database, you need to create tables to store the data in the database. Tables are made up of rows and columns, where each column corresponds to an attribute of the entity to which the table refers. Every row represents an instance of the entity described by the database table.
Specific data relating to each attribute is stored in the rows corresponding to each column.
Types of Databases
Some databases are small enough to be created and contained on your desktop computer while others are so large that they are stored on network servers or mainframe computers. Database management software applications such as Microsoft Access are utilized to manage databases small enough to be stored on a desktop computer. Individuals use these programs to perform specific tasks to manage data for small research projects.
Some databases are so large that that they must be stored on a server or mainframe computer and accessed through a database management system. Some public databases can be accessed online for a fee. These are referred to as information utilities or online services. An example of this is the Microsoft Network. These online services provide access to a myriad of information sources concerning weather, news, and technology.
Even specialized public databases can be accessed online. There are many other types of large databases. Many museums have put artwork online, creating virtual art museums. Most university libraries have created electronic databases to compliment or substitute for their card catalogues.
Relational databases are, by far, the most commonly used type of database.
They depend on a sound theoretical basis in relational algebra. You do not need to understand relational theory to use a relational database (which is a good thing), but you do need to understand some basic database concepts.
Relational databases are made up of relations, more commonly called tables. A table is exactly what it sounds like, which is a table of data. If you have used an electronic spreadsheet, you have already used a table. Look at the sample table in Figure 7-2. It contains the names and addresses of the customers of a bookstore named "Boring Books".
The table has a name (Customers); a number of columns [Name, Address, City] , each corresponding to a different piece of data; and rows that correspond to individual customers.
Each column in the table has a unique name and contains different data. Additionally, each column has an associated data type. For instance, in the Customers table in Figure 7.2, you can see that CustomerID is an integer and the other three columns are strings. Columns are sometimes called fields or attributes.
The various data models that came before the relational database model, such as
the hierarchical database model and
the network database model,
were partial solutions to the never-ending problem of how to store data efficiently.
The relational database model is currently the best solution for both storage and retrieval of data. Examining the relational database model from its roots can help you understand critical problems the relational database model is used to solve; therefore, it is essential that you understand how the different data models evolved into the relational database model as it is today. The evolution of database modeling occurred when each database model improved upon the previous one. The initial solution was no virtually database model at all: the file system (also known as flat files). The file system is the operating system. You can examine files in the file system of the operating system by running a dir command in DOS, an ls command in UNIX, or searching through
the Windows Explorer in Microsoft Windows. The problem that using a file system presents is no database structure at all.