DBMS: View of Data, Data Abstraction, and Data Independence Explained

📘 DBMS – View of Data, Data Abstraction & Data Independence

📌 DBMS & Database Definition

Database: A database is a collection of interrelated data and a set of programs that allow users to access and modify data.

DBMS: Database Management System is a software system that allows users to define, create, maintain, and control access to databases efficiently.

The major purpose of a database system is to provide users with an abstract view of the system, hiding details of how data is stored and maintained. Complexity should be hidden from users.

📌 View of Data

The View of Data refers to how data is perceived or accessed by different users. It represents the organization and presentation of data at different levels.

• Physical View: How data is stored on storage devices.
• Logical View: How data is logically organized (tables, relationships).
• External/View Level: Specific view for a group of users or applications.

Importance: Provides security, simplifies interaction, and shows only relevant data.

💡 Data Abstraction

Data Abstraction is the process of hiding internal details and showing only relevant information to the user. It helps simplify user interaction with complex databases.

📊 Levels of Data Abstraction

• Physical Level: Lowest level of abstraction. Describes how data is stored internally (e.g., index, B-tree, hashing, storage blocks).
• Conceptual/Logical Level: Middle level. Describes what data is stored and relationships among data. Managed by DB Administrator.
• View/External Level: Highest level. Shows part of database for specific users. E.g., bank tellers see customer accounts but not payroll data.

🔑 Data Independence

Data Independence is the ability to change schema at one level without affecting higher levels:

• Logical Data Independence: Changes in logical schema (tables, attributes) do not affect external views.
• Physical Data Independence: Changes in physical storage (file structures, indexes) do not affect logical schema.

Importance: Reduces maintenance, ensures users and applications are unaffected by internal changes.

🎯 Example

Consider a bank database:

• Customer: cust_id, cust_name, cust_street, cust_city
• Account: acc_num, balance
• Employee: emp_name, salary

At Physical Level: records stored as blocks in memory or disk.

At Logical Level: described using record type definitions:

type customer = record
  cust_id : string
  cust_name : string
  cust_street : string
  cust_city : string
end;

At View Level: Applications hide data type details, users see only relevant info.

✍️ Exam Tips / Possible Questions

• Define DBMS and Database.
• Explain purpose of DBMS in 3–4 points.
• Define View of Data with levels and examples.
• Define Data Abstraction and levels (Physical, Logical, View).
• Define Data Independence with Logical & Physical types.
• Possible Questions:
  • Define View of Data with example.
  • Explain Data Abstraction and its levels.
  • Explain Data Independence with examples.