Relational Databases

Database

• Large collection of data in an organised format to allow access and control

• DBMS Database Management System - Special software that helps to maintain the database and control its use.

• DBA Database Administrator (or team) maintains the database(s)

Relational Database RDB

• Database based on the mathematical theory of relations (Ted Codd, IBM)

• Not to be confused with relationships which

are logical connections between data.

A definition

• Logical– The way things appear to be (to the user)

• Physical– The way things really are (on the computer)

What makes RDB special?

• Data is tabular, we can view it in columns and rows

• There are no pointers or physical connections to represent relationships

• Uses an engine to match values “on the fly”.

• The order or columns and rows should not matter.

What are the benefits?

• You don’t get into a mess of broken pointers• You can use tabular data to generate more tabular data

• You can more easily add or delete rows and you can split and merge data more easily

• You can store tables in different locations• You can control row and column access• You can sort data

• Data management can be separated into functions• You only need one language to do everything

What is SQL

• SQL is Structured Query Language• It is not perfect but it is the standard• It varies a little between products• It is composed of– SQL Query– DCL Control– DDL Definition – DML Manipulation

DBA Role

• Recovery (The most important priority).– Is the database in a consistent state at a point in time?

• Access– Are we protecting the data properly?– What are the users and roles and what access do they

have?– What are the privacy requirements?

• Integrity– Can we trust the data?– How do we make structural changes?

Advanced Topics

• Concurrency– Multiple users accessing the same data at the same time– Locking– Versioning

• Transactions– All or nothing unit of work

• Distribution– Distributed data (Replication)– Distributed access

• Tuning– Optimising the database performance– What queries are taking the longest time?– What strategies can we use to improve performance?