Module5 Databases
A simple definition of a database is: A structured collection
of related data about one or more subjects. In normal daily life we
make frequent use of databases, and probably don’t realize it. Here
are a number of simple examples:·
The telephone directory·
Bus or train timetable·
Personal address book·
Filing cabinet
File: a collection of records related by subject. · Product list.· Train
Times.
Record: Information about a single item (entity).· The customer
Field: The individual data items held for each record.e.g The customer
- Name, Business, Address, Telephone Number etc
Fields are further defined in terms of size and the type of information
that they contain.
Databases generally come in one of two styles.
1/ Flat file database
Flat File Databases are basically used for simple lists and may have duplication of data much like a simple record card system.
2/ Relational database
Relational Databases are those where the data is held in a number of cross-referenced files in order to reduce duplication. They make it easier to find, analyze, maintain and protect your data because it is all held in one place.
Types of relationships When a customer makes an order, it may be for more than one product. In other words there could be many products in one order. This is known as a one-to-many relationship. A less common relationship is one-to-one. Many-to-many relationships are not allowed in Access: they are resolved into one-to-many relationships by setting up additional linking tables.