Database management systems

A database management system (DBMS) is software for creating and managing databases. Examples are MySQL, Oracle, PostgreSQL, SQL Server, Microsoft Access and MongoDB. A DBMS hides the details of how data is stored, giving users a simple, abstract view of it.

Moving the school's files into a database also fixes the redundancy. SName is removed from ATTENDANCE (it is already in STUDENT), and guardians' details move into their own GUARDIAN table, where each guardian is stored once, with a unique GUID (guardian ID).

Some key terms:

• Schema: the design of the database: its tables, their columns and data types, the constraints, and the relationships between tables.
• Constraint: a restriction on the data a column can hold, such as NOT NULL (the value cannot be empty) or UNIQUE (no two rows can have the same value). Constraints make data entry more reliable.
• Meta-data: the DBMS stores the schema and constraints in a data dictionary (or catalog).
• Instance: the actual data in the database at a given moment. The schema stays the same, but the instance changes as data is added, changed or removed, so one schema has many instances over time.
• Query: a request for information from the database.
• Data manipulation: changing the data: insertion, deletion and update.
• Database engine: the part of the DBMS that carries out these operations.

For example, when a new student, Rivaan, joins the class, his details are inserted into STUDENT, and his guardian's details into GUARDIAN (if the guardian is new).