Basic Concepts Of Database and Database Management Systems (DBMS)

1. Concept of Database

• Data: Raw facts without organization.
• Database: Organized collection of inter-related data ensuring safety, security, and integrity. Stores data in tables (relations).

2. Database Management System (DBMS)

• DBMS: Software for storing, maintaining, and using databases.
• Database System: Combination of database and DBMS software.
• Examples: Oracle, MS SQL Server, MS Access, Paradox, DB2, MySQL (open source and freeware).

3. Advantages of Database Systems

• Reduces Redundancy: Avoids data duplication.
• Controls Inconsistency: Prevents data discrepancies by centralizing storage.
• Facilitates Data Sharing: Allows multiple users to access data.
• Ensures Security: Protects data from unauthorized access or modifications.
• Maintains Integrity: Enforces rules to ensure data validity (e.g., date format).

4. Concept of Data Model

• Data Model: Representation of data organization in the database.
  • Relational Data Model: Data stored in tables (rows and columns).
  • Network Data Model: Data represented by records linked with pointers.
  • Hierarchical Data Model: Data organized as a tree with a root and child records.
  • Object-Oriented Data Model: Data represented as objects within classes.

5. Basics of Relational Data Model

• Relation (Table): Two-dimensional matrix of data with rows and columns.
  • Atomicity: Columns have unique names and indivisible values.
  • No Duplicity: Unique rows; no identical rows allowed.
  • Homogeneity: Columns contain similar data types.
  • Ordering: Rows and columns can be unordered.
• Key Terms:
  • Domain: Set of possible values for a column.
  • Tuple/Record: Row in a table.
  • Attribute/Field: Column in a table.
  • Degree: Number of columns in a table.
  • Cardinality: Number of rows in a table.

6. Concept of Keys

• Primary Key: Unique identifier for each record in a table. Each table should have one.
  • Examples: Student Admission Number, Book Accession Number, Employee ID.
• Candidate Key: Any column or set of columns that could serve as a primary key. One is chosen as the primary key.
  • Alternate Key: Candidate keys not chosen as the primary key.
• Foreign Key: A non-key attribute that refers to the primary key of another table, used to establish relationships and enforce referential integrity.

Example of Keys

• Student Table:
  • Primary Key: Admission_No
• • Candidate Keys: RollNo, Admission_No
• • Alternate Key: RollNo (if Admission_No is chosen as primary)