Database Management
Introduction
What is “Data”?
► A representation of raw facts which has no meaning assigned ► Generally, operations are performed on data or data items to supply some information about an entity.
What is a Database?
A database is an integrated and structured collection of stored operational data used (shared) by application systems of an enterprise
Examples of Databases • Medical records • Bank accounts • Stock control • Telephone directories • Stock market prices
Universe of Discourse A database is a model of some aspect of the reality of an organisation. It is conventional to call this reality a universe of discourse (UOD), or sometimes a domain of discourse.
Database Users End user – Naïve or casual user – Accesses database either through forms or through application front-ends – More sophisticated ones generate ad hoc queries using DML
Application programmer/developer
– Designs and implements applications that access the database (some may be used by end users) – Database administrator (DBA)
– Defines and manages the conceptual schema – Defines application and user views – Monitors and tunes DBMS performance (defines/modifies internal schema) – Loads and reformats the database – Responsible for security and reliability
Data Dictionary – Metadata
• The dictionary or catalog stores information about the database itself • This is data about data or ‘metadata’ • Almost every aspect of the DBMS uses the dictionary
The dictionary holds:
• Descriptions of database objects (tables, users, rules, views, indexes,…) • Information about who is using which data (locks) • Schemas and mappings
A database Management System
A database management system (DBMS) is an organised set of facilities for accessing and
What is “Data”?
► A representation of raw facts which has no meaning assigned ► Generally, operations are performed on data or data items to supply some information about an entity.
What is a Database?
A database is an integrated and structured collection of stored operational data used (shared) by application systems of an enterprise
Examples of Databases • Medical records • Bank accounts • Stock control • Telephone directories • Stock market prices
Universe of Discourse A database is a model of some aspect of the reality of an organisation. It is conventional to call this reality a universe of discourse (UOD), or sometimes a domain of discourse.
Database Users End user – Naïve or casual user – Accesses database either through forms or through application front-ends – More sophisticated ones generate ad hoc queries using DML
Application programmer/developer
– Designs and implements applications that access the database (some may be used by end users) – Database administrator (DBA)
– Defines and manages the conceptual schema – Defines application and user views – Monitors and tunes DBMS performance (defines/modifies internal schema) – Loads and reformats the database – Responsible for security and reliability
Data Dictionary – Metadata
• The dictionary or catalog stores information about the database itself • This is data about data or ‘metadata’ • Almost every aspect of the DBMS uses the dictionary
The dictionary holds:
• Descriptions of database objects (tables, users, rules, views, indexes,…) • Information about who is using which data (locks) • Schemas and mappings
A database Management System
A database management system (DBMS) is an organised set of facilities for accessing and
References: state (country_code, state_code); Dropping a Table ■ To remove the definition of a table from the data dictionary, you have to use the drop table command. The format of this is Dropping (deleting) a Table drop table tablename; ----------------------- Second Normal Form