What is Database?
A '''database''' is a [[Computer|computer system]] for storing and taking care of data (any kind of [[information]]). When the software that runs a database is separate from the programs that use the database, it is called a '''database engine'''. Information stored inside a database is usually stored in an organized way. Data about a person that would have been written on a piece of paper before databases would be stored in a '''record''' in a database. A collection of person records that would have been an address book before databases would be stored in a '''file''' or '''table'''. == Uses for database systems == Uses for database systems include: * Storing data. * Searching for specific information within the data. * Allowing multiple people to look at and change the data at the same time. * Managing who is allowed to see the data and who can change it. * Managing rules about the data. A rule might say ''November has 30 days''. This means if someone enters ''November 31'' as a date, this date will be rejected. == Changing data == In most databases, data can change. This also means, that in many cases, changing the data needs to be done in several steps. This is because the data is often stored in more than one tables or files that need to work together to make sense. In many cases all the steps that are needed for a given change are grouped in what is called a [[Database transaction|transaction]]. If something goes wrong, all the steps are undone. Being undone is another way of saying the transaction was ''rolled back''. If all the steps are successful, they can be made a permanent part of the database. People talk about a transaction being ''committed''. Both rollback and commit affect all the steps in a transaction. The reason why a transaction is rolled back could be that the user or program did not want to finish the change. It could also mean that there is a problem. The database system itself might have a problem during the change. The change might break the rules of the data. == Guarantees about