Topic 6: Relational Database Management Systems

What is Data Dictionary?

- A central store of information aout data such as tables, field names, field types, field lengths and validation used on the field.

What is SQL?

- A data manipulation language used to perform searches and sorts in a database - Instead of using the query wizard in access, code is typed into and editor instead - For example, UPDATE will update data in the database whilst SELECT will find specific data in a database.

Functions RDBMS has:

- Create, edit and search data - Create and maintain a data dictionary - Back up and recovery of data - Security functions such as check passwords and access rights - Allow applications to access the data

Disadvantages of Distributed Databases

- If data is transferred it presents more a security risk from hackers - As all the data is not stored in one location, if a local site does not have adequate backup then this data might be lost to others. - Heavy reliance on networks and communications which may not always be reliable.

Advantages of Distributed Databases

- New locations can be added to the database without the need for rewriting the entire database - Easy to backup and copy data from one server to another - If one server fails then the other servers can be used.

Distributed Databases

A distributed database has data stored on a number of computers at different locations but appears as one logical database.

What is a popular RDBMS?

Microsoft Access

Definition

Relational Database Management Systems (RDBMS) are used widely by businesses and organisations and have a number of significant benefits for their users.

What does SQL mean?

Structured Query Language