Cambridge A-Level Computer Science 9618 – DBMS Features vs File‑Based Approach
8.2 Database Management Systems (DBMS)
Objective
Show understanding of the features provided by a Database Management System (DBMS) that address the issues of a file‑based approach.
1. Problems with a File‑Based Approach
Data Redundancy and Inconsistency – Same data stored in multiple files leading to wasted space and contradictory values.
Lack of Data Independence – Application programs are tightly coupled to file structures; any change requires program modification.
Limited Data Sharing – Files are usually accessed by a single program; concurrent access is difficult to control.
Poor Security and Integrity – No central mechanism to enforce access rights or integrity rules.
Complex Data Retrieval – Programs must contain procedural code to locate and combine data, making queries cumbersome.
Difficulty in Recovery – No systematic way to restore data after a crash or corruption.
Limited Backup and Maintenance – Each file must be backed up separately; version control is manual.
2. DBMS Features that Resolve These Issues
The following DBMS features directly address the shortcomings listed above.
Issue (File‑Based)
DBMS Feature
How It Helps
Data Redundancy & Inconsistency
Normalization & Centralised Storage
Data is stored once in tables; relationships eliminate duplicate copies, ensuring consistency.
Lack of Data Independence
Logical & Physical Data Independence
Applications interact via a logical schema; changes to physical storage do not affect programs.
Limited Data Sharing
Concurrency Control (Locking, Timestamping)
Multiple users can access the database simultaneously while the DBMS resolves conflicts.
Poor Security & Integrity
Access Control & Integrity Constraints
Roles, privileges, and declarative constraints (e.g., primary keys, foreign keys) enforce correctness.
Complex Data Retrieval
High‑Level Query Language (SQL)
Declarative statements retrieve and manipulate data without procedural code.
Difficulty in Recovery
Transaction Management (ACID) & Logging
Atomic transactions and write‑ahead logs allow rollback to a consistent state after failures.
Limited Backup & Maintenance
Automated Backup, Recovery Utilities, Data Dictionary
System‑wide backup tools and a metadata repository simplify maintenance and version control.
3. Summary of Key DBMS Capabilities
Data Independence – Separates application logic from data storage.
Reduced Redundancy – Centralised, normalized tables.
Concurrency Control – Ensures safe multi‑user access.
Transaction Support (ACID) – Guarantees reliability and recoverability.
Security & Integrity – Role‑based access and declarative constraints.
Powerful Query Language – SQL for expressive data manipulation.
Data Dictionary – Stores metadata about structure, constraints, and users.
Backup & Recovery Tools – Streamlined data protection.
Suggested diagram: Comparison of a file‑based system (multiple isolated files) versus a DBMS architecture (centralised DBMS with applications, users, and utilities interacting through SQL).