P3C6: Databases

Databases - Outlines

1. A flat file consists of a large number of records each of which comprises a number of fields.
2. Each field has its own data type and holds a single item of data.
3. Limitations of flat-file systems:
• separation and isolation of data
• duplication of data
• data dependence
• data inconsistencies
• difficulty in changing applications programs
4. Relational databases store data in tables.
5. Normalization is a set of formal rules that must be followed after a set of table is designed.
6. Normal forms (NF):
• 1 NF: It doesn't have a repeated group of attributes
• 2 NF: There are no non-key fields attributes which are dependent on only part of the primary key
• 3NF: There are no dependencies between non-key attributes
7. An entity - relationship (E-R) diagram shows the entities in the database and the relationships between them.
8. A relational database gives the following advantages over flat files:
• Data are contained in a single software application.
• Duplication of data is minimized.
• Data inconsistency is reduced.
• The volume of data is reduced leading to faster searching and sorting of data.
• Data structures remain the same even when tables are altered.
• Existing programs don't need to be altered when a table design is changed or new tables created.
• Queries and reports can be set up quickly.
9. A primary key is used to uniquely identify a record or row in a table.
10. A foreign key attribute links to a primary key in a second table.
11. A secondary key is used to get fast access when searching on this attribute.
12. Different categories of user can see different views of the data - only what is needed for their job.
13. Terminals in public areas may be refused access to sensitive data, even if the user has access.
14. A DBMS (Database Management System) is a piece of software that provides the following facilities:
• a data definition language (DDL) that the database designer uses to define the tables of the database
• a data dictionary that contains all design information
• a data manipulation language (DML) for inserting, selecting, updating and deleting data records
• backup of the database data
• control of multi-user access to the data.
15. The DML and DDL used by all modern database software is Structured Query Language (SQL).