tributed databaseDatabases support three kinds of data. Transient data lasts only for the invocation of a single program. Stable data is recoverable data that is resilient to failure. Persistent data is accessible beyond the process that creates it. In relational databases, persistency is obtained by all data stored in tables. SQL operations are automatically applicable to these data and the database stores all changes. Database transaction is a unit on a database that takes it from one consistent state to another consistent state. Relational database transactions are short. The system strives to complete them in the shortest possible time so that the database resources can be freed for other concurrent transactions. Transaction management serves the purpose of database recovery. The principal devices to recover the database from failure are logging and backup. Relational databases use techniques that are typically more advanced for managing recovery. Authorization and security is achieved by providing a discretionary control over access to objects according to privileges. Consistency and integrity are obtained through the implementation of referential integrity between tables. A query language is a deceptive term standing for a database manipulation language. SQL is used to query and update database tables. It has a closure property. It takes a table as input and returns another table as output. Data independence is the degree to which changes to logical and physical data structures do not affect existing programs. Because they are based on a logical model, relational databases exhibit a very high degree of physical independence. Changes and deletions are much more troublesome. In relational databases, the queries are always evaluated on the server. This improves performance for typical business-like transactions that process large data volumes before returning short answers. To get data from a database, we is...
