What is a relational database?
The concept of a relation database can be thought of as a collection of tables that are connected together by Primary and Foreign keys. A table is like an Excel spreadsheet that is a file based system with cells as fields and rows as records. A table is contained in a DBMS. The purpose of related tables are to reduce the amount of redundant information. One table could contain contact information, another table could contain product information, and another table could contain inventory information and so on.
How is it structured?
The data is contained within table and the tables are connected together with primary and foreign keys.
Indicate commercial database that are sold to the public that are relational in nature.
There are two kinds of database products. One is the product that a database application is developed in such as Microsoft SQL http://www.microsoft.com/sql and another is an actually application that uses a database that is pre-structured such as MOLDTRAX at http://www.moldtrax.com . This commercial relational database uses an Access database. It has seventeen tables with seventeen primary and foreign key relationships. It has sixty custom queries that use one to many relationships to define a view for a form or report.
What are the advantages and disadvantages?
The biggest advantage is the over reduction in redundant information. Another advantage is the ability to relate information and produce queries results that would not otherwise be possible in a single table.
The biggest disadvantage is the complexity in knowledge required for an administrator or developer to build, deploy and maintain such a system. Therefore is can be more expensive to use.
In most companies there are measure in place to deal with data contained in a single location such as:
- Data replication to another server
- RAID 5 hard drives in which the data is contained on several hard drives at the same time live
- Cluster Servers in which the same data runs on several servers at the same time in a RAID 5 environment
- There are two kinds of Backup Agents on real time data backup and the other is night agent backups.
- The database systems also contain the ability for them to be backed up or dump their data to a text file manually or on a schedule.