Database management systems(DBMS)- are collections of tools used to manage databases. Four basic functions performed by all DBMS are:
* Create, modify, and delete data structures, e.g. tables
* Add, modify, and delete data
* Retrieve data selectively
* Generate reports based on data
A short list of database applications would include:
*
* Inventory
* Payroll
* Membership
* Orders
* Shipping
* Reservation
* Invoicing
* Accounting
* Security
* Catalogues
* Mailing
* Medical records
Database Components
Looking from the top down, databases are composed of related tables, which in turn are composed of fields and records.
Field
A field is an area (within a record) reserved for a specific piece of data. Examples: customer number, customer name, street address, city, state, phone, current balance.
Fields are defined by:
* Field name
* Data type
Character: text, including such things as telephone numbers and zip codes
Numeric: numbers which can be manipulated using math operators
Date: calendar dates which can be manipulated mathematically
Logical: True or False, Yes or No
* Field size
Amount of space reserved for storing data
Record
A record is the collection of values for all the fields pertaining to one entity: i.e. a person, product, company, transaction, etc.
Table
A table is a collection of related records. For example, employee table, product table, customer, and orders tables.
In a table, records are represented by rows and fields are represented as columns.
Database
A database is a collection of related tables. It can also include other objects, such as queries, forms, and reports. The structure of a database is the relationships between its tables.
Relationships
There are three types of relationships which can exist between tables:
One-to-One
One-to-Many
Many-to-Many
The most common...