Now we have the people in one table and the magazines in another table. How do we know who is subscribed to what? This is where the Relational Database gets its name. So far we have discussed some of the basic elements of a database. Now we will take those basic elements and make them relate to one another so that the information being stored remains logically linked together. Hence the term Relational Database.
Now, using our example above we have a table of subscribers (contacts) and a table of magazine information (magazines). So, how do we know who subscribed to what? We make another table that links the two tables we already have together.
Contact ID |
Magazine ID |
1 |
2 |
2 |
1 |
2 |
2 |
3 |
2 |
This table places a link between the contact table and the magazine table using each tables unique ID number. So, by referring to the table above you can see that John Smith has subscribed to Hot Bike Magazine, Laurie Wayman subscribed to both Ladies Home Journal and Hot Bike Magazine and Paul Johnson subscribed to Hot Bike Magazine.
But what about that Primary Key mentioned earlier? The Contact ID numbers are used more than once. Nothing is unique. This is true. In this instance we are using Foreign Keys. A Foreign Key basically means that the number used in a Foreign Key column is not necessarily unique to the table it is in but is unique to the table it is referring to. In this case Contact ID is unique to the Persons table but not necessarily unique to the Magazine table. These are the basics of a relational database.
What is the major difference between a File Based DBMS and a Server Based DBMS?
The primary difference between the two database types is in their use.
An example of a file based DBMS is MS Access, which is primarily used as a local, standalone database on one computer. These databases tend to be smaller and less complex requiring less computing power. On the other hand, a server based DBMS, such as MS SQL Server, is a database program which utilizes server and client side installed software. Utilizing the storage and computing capabilities of a server, MS SQL Server can host complex databases.
