Chapter 2: Basic Concepts and Terminologies of Databases

Field: A unit of data consisting of one or more characters (e.g., Name).
Record: Collection of related fields (e.g., Student Record).
File: Collection of related records (e.g., Student File).

Field Types:

• Fixed Length: Predefined number of bytes. Data cannot exceed length. Wastes space if data is short.
• Variable Length: Occupies space according to data entered. No extra blank spaces.

Definition: A two-dimensional array containing data about an entity. Rows (Tuples) represent records, Columns (Attributes) represent fields.

Properties:

• No Duplicate Rows: Every row must be unique (ensured by Primary Key).
• Order Insignificant: Row and Column order does not matter.
• Atomic Values: Intersection of Row/Column must contain atomic (indivisible) value.

Key: An attribute or set of attributes that uniquely identifies a tuple.

• Primary Key: Unique identifier for a row. Cannot be NULL. (e.g., RegNo).
• Composite Key: Primary key consisting of two or more attributes (e.g., RollNo + Subject).
• Candidate Key: Any attribute that can be selected as Primary Key (e.g., RegNo, RollNo).
• Alternate Key: Candidate keys not selected as Primary Key.
• Foreign Key: Attribute in a child table that matches Primary Key in parent table. Enforces referential integrity.
• Secondary Key: Attribute used for retrieval (non-unique, e.g., City).
• Sort/Control Key: Attribute used to physically sequence stored data.

Definition: A virtual table derived from one or more base tables. It does not exist physically but is created dynamically.

Purpose:

• Security: Restrict access to specific data (e.g., hiding Salary).
• Simplicity: Simplify complex queries for End Users.
• Independence: Isolate application from changes in base table structure.

CREATE VIEW Student_View AS
SELECT StudNo, StudName
FROM Student
WHERE StudGender = 'M';

End User: Person who interacts with the database application. Does not need technical knowledge.

Data Administrator (DA): Responsible for defining data standards, policies, and procedures. Manages data definitions and dictionary.

Database Administrator (DBA): Responsible for technical implementation, performance, security, backup, and recovery of the database system. Tasks include:

• Software Installation
• Monitoring Performance
• Assigning Permissions
• Executing Backup/Recovery