Ohne Titel

databases

1. relational databases

2. flat file data base

3. A database is a system designed to store data in an organised way, making it easier to search for the information you need. A database needs to be reliable, consistent and have a structure that suits the data you collect. A database is stored in a format such as a CSV file saved on a hard drive. Databases are persistent, which means that the structure is fixed in place. A database is persistent system which means it is fixed in place

4. An example of a paper database could be a phonebook or yellow pages. Examples of screen based databases could be itunes and any online store

5. Validation checks that the correct type of data is entered Verification checks that the data is actually the data you want.

6. A relational database divides the data within the database into different tables with each table focusing on a particular entity. This ensures that most data is stored only once. For example, a newsagents stores information on its customers. It also needs to store information on the newspapers and magazines each customer receives. As this information is a different entity we need to have a separate table for this data.

7. Each table should have a primary key. This is a field chosen to be unique for each record. Usually this is some sort of reference number. A foreign key is used to link tables together and create a relationship between them. It is a primary key in one table that is linked to a field in another table.

8. One of the strengths of a DBMS is the query language called SQL, that it supports. The first term SELECT means extract from the database without modifying them in any way. The star * means “All records” This is similar to the wildcard in a QBE (Query By Example). The FROM keyword is used to identify the table to be accessed. “Employees” is the name of the table to be accessed.