DATABASE What exactly is a database How do databases work? What's the difference between a spreadsheet database and a "real" database?

What is a database? "A database is an organized collection of information".

Database Basics You use databases all the time, although you might not realize it! For example: – Telephone directories – The list of contacts on your phone – Online product catalogues and shops

Database Basic The important thing about databases is the way that the information is organized. Let's look at a simple telephone directory as an example. It has entries like this: – [Tupou] [Sione][Hala Hekoni][Ma’ufanga Tt ][21333] You could simply enter all the information as shown above and then print your directory.

Problem The problem is that if you wanted to do something else with the data - for example, – organise it in a different way – find all the people in the Maufanga area – or publish a different version of the directory, you would have a lot of work to do

Database Basic The listing consists of five different pieces of information: [Last name] [First name] [Address (Road)][Area [(Village)] [Phone number ] – We refer to each of these bits of data as a field. – Each group of fields belonging to the same item is called a record. – And each collection of records of the same type of data is called a table.

Flat File Database Information above can be stored in a spreadsheet: One worksheet is a table Each row in the worksheet is a record Each column is a field – The structure described above is what we refer to as a "flat-file" database: it's a one-dimensional collection of data about one topic. – fine for many purposes

Relational Database That's why we have relational databases. So that information such as discussed in slide #5 would be very easy to used

Relational Database In a RD, we need to maintain more complex structures in which data from two or more tables is linked together. examples are: – Families (parents and children) – Products and parts – Manufacturers and Products – Classes and Students – Customers and Invoices

You might be tempted to think? "Why can't I just add more fields if I need more information?" – For example, if your database contains information about products and you want to add a list of the components that make up each product, why not just add fields for "component 1", "component 2" and so on? Well, yes, you can, but you'll run into limitations such as: – Some products might have only one component; another might have 20. How do you know how many fields to add?

You might be tempted to think? What if the same component is used in a number of different products? What if you wanted to find a particular component? – You would have to search all those additional component fields, because you wouldn't know which one it might be in!

You might be tempted to think? What if you wanted to produce a report listing all your components and their prices? – That would be extremely difficult.

That's why we have relational databases In the parts and components example, we would have two tables: Parts and Components. The basic product details would go into fields in the Products table, and all the details about each component would go into a record in the Components table.

Important thing needed One more important thing is needed: something to tell the database how the records are linked together - in other words, which components belong to which products. For this purpose, each record must have a unique identifier of some sort. It can be simply a sequential number, or an alphanumeric code of some sort that you devise. The import things are that it must be UNIQUE for each record and it must never change.

Simple Relationship between products and components tables This illustrates a "many-to-one" relationship: many components can be related to one product via the product id. So, to find all the components that comprise the product whose ID number is 1234, you would search the components table for all records whose product id is There might be just one, or there might be dozens.

But what if the same component can be used in a number of different products? That's what we call a many-to-many relationship: many components can be related to many products. To facilitate this, we need to introduce an additional table just to keep track of those relationships.

Relations The relations table would contain one record for each link between a product and a component. With this sort of structure, you can easily produce reports showing all the components belonging to a product, or all the products in which a particular component is used.

A way forward DB Guide 10/DB%20Guide.pdf 10/DB%20Guide.pdf Start with “ first step with Access” m m Database Design ase-design-101.aspx ase-design-101.aspx OR ANY RESOURCES YOU LIKE …..

Activities You should have done practical 1 – 3 DB Designing Designing