Databases

Databases

1. A data base is an persistent and organised store of data

   • Example 1: A search engine
   • Example 2: School registers

2. Here is how you describe the information

   • The area in which you can write an aspect of a person is called the field. For example, the part where you are able to write a persons first name
   • All of the data about a person is called a record

3. Flat file databases

   • Advantages
     • All records kept in one place
     • Easy to understand
     • Simple sorting and filtering can be taken out
     • Can use a spread sheet to store it
   • Disadvantages
     • Easy to generate dublicate records
     • Harder to update
     • Very Inefficient
     • Harder to change data format when the data has been added
     • Harder to perform complex queries
     • No security

4. Relational database

   • This is when 2 or more databases are linked.
     • This data will be available when looking at the linked database
     • Advantages
       • Data is only stored once
       • More efficient storage
       • Simple to delete/ modify data
       • Data in other tables are linked and this means that data over the multiple tables are changed together

5. Primary/ Foreign key

   • Primary key is a field which allows all data to be seperately identified
   • A Foreign key is a field which is used to link 2 tables together, it is a field in one table which is linked to the primary key of another table

6. Data integrity

   • This is the ability to 'force' data to be consistent
     • Referential integrity
       • This is the rule which makes sure that the primary key is never duplicated. As well as that, it makes sure that if the primary key is changed, the foreign key is changed in the other tables.
     • Data validation
       • This can be implemented to ensure that data is structured in a specific way. For example, make sure a date is in a certain format

7. An entity

   • An entity is a person, place, thing or concept about which data can be collected about.

8. Attribute

   • Describes the facts, details or characteristics of an entity
     • Car
       • Make
       • Engine size
       • Seats

9. Relationships

   • A link between entities
     • One to one
       • Examples
         • A husband can only have one wife
         • A wife can only have one husband
     • One to many
       • Examples
         • A mother can have multiple children
         • A child can only have one mother
     • Many to many
       • Example
         • A video can be hired by multiple customers
         • A customer can higher multiple videos