Databases

Databases

1. Flat-file & Relational databases

   • only contains a single table of data.
   • Relational: contains two or more tables of data, connected by links called relationships.

2. Reasons to use a database

   • Can sort data- on several fields at once.
   • Can search the data- create queries and search on more than one criterion.
   • Store data in multiple tables.
   • Can produce reports.
   • Can define field types- only allow certain data entry.

3. Key terms

   • Database- an organised structured way to store data..
   • A Field- store one piece of information In a database.
   • A Record- collection of all the fields for one person or thing.
   • Primary key field- uniquely identifies a particular record.
   • A Table- is a collection of records of the same type. EG school database will contain student records.

4. Advantages & Disadvantages

   • Advantages: Store data easier/faster. Takes up less space. Backups can be kept. Data can be extracted and sent to other users. Can be edited. Security options EG passwords.
   • Disadvantages: Need a computer system that works. Hard/software or power crash can cause problems. Computer skills are needed by users. Virus or hacking issues.

5. Verification

   • Checking that data is entered correctly.
   • Double entry EG typing the password twice to check they are both identical, you would do this for a new password.
   • Visual checks EG proof reading.

6. Validation

   • Format checks (Picture check)- only valid numbers and letters are added EG date of birth 27/02/2002.
   • Range checks- Data must be within a range EG month must be within 1-12.
   • Presence check- checks data has been entered.
   • Type checks- checks the type of data being entered EG name must be text.
   • Length check- correct amount of numbers or characters entered EG phone number has 11 digits.
   • Check digits- calculated from other digits scanned through it. Rejected if its different from the original EG barcode.

7. Data types

   • Text/Alphanumeric- Allows text and numbers EG postcode or phone number.
   • Numerical - only numbers EG umber of pets =2.
   • Boolean- Allows one of two options EG M/F.
   • Date/Time- date and/or time EG DOB 27/02/2002
   • Auto number- computer generates a unique number.