Why are relationships important in Microsoft access?

Answer 1

A Relational Database is a Database in which the data it contains is stored in separate Tables, with these tables related to each other. These Tables each hold information on logical groups of Data. For example a company's business data may be stored in different independent but inter-related Tables. They may have a list of Products and a list of Suppliers for those Products. The company would want to know which company supplies each product. For each supplier they would want to know their Name, Address, Contact Details etc. All the data could be put in one table.

However if one supplier supplies 100 different products and all their details are stored for each product this will mean a lot of repeated data and make the table quite large. Also, if any of the suppliers details change, this amendment will have to be made for each product's record. This obviously means a lot more work. There is also the possibility that this change may not be made in every record that requires it and inconsistencies will result in the database. The database may have different addresses or phone numbers stored for the one supplier. The solution is to have one table which stores all the product details and another table that stores the supplier details. In order to make sure that each product is still associated with a supplier a Relationship is set up between the two tables. This is done by having one field common to both Tables. Both fields must be of the same type and size, though its name can be different.

Each Supplier's full details now only appear once in the database, in the Suppliers Table, regardless of the amount of products they supply. Each Product is related to a particular supplier by having the relevant Suppliers Code included in the Products Table. This stops us having to store all the details of the Supplier for each Product as when all the data was being stored in the same table.

As one supplier can have many products and as the supplier appears once in the database, this is an example of a one to many relationship. There are also what are called one to one relationships, where each item is related to only one other and there are many to many relationships, where many things can be related to many others. An example is a music collection where you have many CDs and there are many songs. Each CD has many songs and each song could be on more than one CD.

Answer 2

It shows the different tables involved in the relationships, with lines showing which tables are related to each other and usually a symbol or number to indicate the type of relationship it is. There are different ways of doing that.