Databases

Databases

1. A persistant Store of data

2. DBMS (Database Management System)

   • Security: data must be kept safe from malicious access
   • Creation: involves using software to define and build the structures to hold the data.
   • Maintenance: involves using software to make changes to the data in the database. For example: adding (also referred to as inserting) new data items,deleting existing data items,updating (editing) existing data items

3. USES

   • Marketing
     • Loyaltly Cards
     • Customers Buying Habits
   • WorkPlace

4. Relational Databases

   • A flat file database is when all of the data and fields are all stored in one table.
   • Data Separated into individual tables

5. Databases are organised stores so that the data in them can be accessed and processed as efficiently as possible. The data in a database is collected for some specific purpose and a database is usually set up in response to a need.

6. It is undesirable for applications to be data-dependent. The traditional approach to storing data in a company was for everyone to store their own data separately. A company might have a Sales department dealing with customers and a Training department that trained the same customers on the products they’d just bought. These departments would have kept their own data files, with slightly different versions of the data, rather than sharing one file of data.

   • This data duplication leads to wasted storage space and time wasted entering the same information in different places. The ideal situation is to enable applications to share an integrated database containing all the data needed by the applications. This eliminates data redundancy (unnecessary duplication of data).

7. Data in a database table is organised into rows (records) and columns (fields). Each record in a relational database table corresponds to an entity. In the example table of 'Students' above there are 5 records. Each record corresponds to an individual student. Note that although there are two students called Philip Barker with the same date of birth, they have different Student IDs and are different students.

8. Each table has a primary key. This is a field chosen so that it can uniquely identify each record. Sometimes an existing attribute can be used because it is unique but most of the time some sort of ID is created. Primary keys can be used to link to foreign keys in other tables. A foreign key is the primary key in a different table and it is not necessarily unique.

9. Forms

   • Forms are used to create a user interface for data entry. They allow users to type data into a database using a specially designed form rather than typing directly into a database table. The advantage of forms over typing into tables is that forms can be tailored to only accept certain information or only information in the correct format, i.e. forms provide another means of data validation. Drop down list boxes for data selection make the input of data faster and reduce typing errors. In the Contact Details form below, the entry fields for Company, Job Title and Category are selected from a list rather than typed by the user making the data entry