Relational Databases

Relational Databases

1. File

   • Table
     • Record
       • All data about one person or thing.
         • Quite a few fields can be used to make a record e.g. name, address,age,date of birth.
     • Field
       • Primary Key
         • A field in a table which is unique and this helps to identify records or people
         • Referential integrity
           • Every foreign key value has a matching value in the appropriate primary key field.
       • A piece of data related to a person or thing
       • Foreign keys
         • A primary key in one table inserted as a normal field in another table
       • Attributes- Name,Age,Address
     • Records are stored in here.
     • Made of quite a few pieces of information, e.g. First Name, Address, Age
     • Entities- objects,people,things
     • RelationShips:
       • One to Many
         • Where one entity can have many relations- such as 1 doctor has many patient or 1 student has many exams
       • Many to many
         • where many entities can have many relationships e.g. 1 video can be hired by several customer BUT those customers can hire several videos
       • One to One
         • When one entity can only be related to one entite e.g. 1 man has 1 wife.
   • Many tables are stored in a file, this is the database.

2. Vast amounts of info can be stored!

3. Queries can be run to search for specific records.

   • Searching is what a query does.
     • Parameters are just search criteria
     • 4 Types
       • Static-the parameters stay the same for ever.
       • Dynamic- you can change the search result sto what you need
       • Simple- only 1 parameter is used at a time
       • Complex-more than one parameter is used

4. Reports can be created from data stored or queries run

   • presents data taken from a query or from tables in a preformatted attractive manner

5. Validation can be used to reduce errors.

   • Validation!
     • Makes sure that the data is: accurate sensible,within acceptable boundaries.
       • Range Check- makes sure that the value entered is between 2 preset boundaries
       • Lookup Check-Allows only a limited amount of item to be selected
       • Length Check- checks that the data entered is a certain length.
       • Presence check- makes sure something is enteredin the field
     • NEVER MAKES SURE THAT THE DATA IS CORRECT!!!
   • Verification
     • Making sure that the data on the source document is the same as the object doucument.
       • Proof Reading- double checking your work basically.
       • Double entry- where two people input the same document and these are then compared any differences are then noted and rectified.

6. Forms Used to enter data.

   • A window/Screen with multiple spaces to enter data.