Data vs information; plain files and their problems

1 · The Hook

A college keeps its student records the old way. The exam cell has a spreadsheet of students. The library has its own file. The hostel office has a third. Each office typed in Asha's name, roll number and phone number separately.

Asha changes her phone number and tells the exam cell. A month later the library tries to call her about an overdue book and reaches a stranger. Nobody did anything "wrong", yet the college now holds two different phone numbers for the same person. This lesson explains why keeping data in separate files breaks in exactly this way, and what a better system must fix.

2 · Predict First

Three offices each keep their own copy of every student's phone number. A student updates her number at one office only. How many of the college's copies of her number are now wrong, and can the college tell which one is right?

Make a guess in your head. The answer opens Section 3.

3 · Core Concept

Predict First — the answer

Two copies are wrong, and the college cannot tell which copy is right by looking at the files alone. Three copies of one fact means three places to update. Miss any of them and the copies disagree. This disagreement is called inconsistency, and it comes directly from storing the same fact more than once (redundancy).

Data vs information

Data is raw recorded facts: Asha, 9.1, C1. On its own a value means little.

Information is data processed into something meaningful: "Asha has the highest CGPA in the CS department." Information answers a question; data is what you compute it from.

A database is a collection of related data about one organisation (a college, a bank, a railway), stored so that many questions can be answered from it.

The file-processing approach

Before database systems, each department wrote its own programs that kept data in its own files. This is a file-processing system. It works while the organisation is small. As it grows, the same problems appear every time:

Atomic means "all or nothing": a multi-step task should either finish completely or leave no trace. Concurrent means "at the same time".

What a better system must do

Store each fact once (or keep copies under control), answer new questions without new programs, enforce rules in one place, make multi-step tasks all-or-nothing, let many users work at once safely, and control who sees what. Software that does this is a database management system, the subject of the next lesson.

4 · Visual

Separate files per office: one update reached only one copy.

File-processing system                 Database approach
----------------------                 -----------------
Exam program  --> exam.xlsx            Exam program    \
Library prog  --> library.txt          Library program  >--> DBMS --> one database
Hostel prog   --> hostel.csv           Hostel program  /
(each program owns its own file)       (programs ask the DBMS; data stored once)

Left: every program owns its data. Right: programs share one database through one manager.

5 · Worked Examples

Example 1 Easy

Classify each as data or information: (i) C2, (ii) "3 students failed DBMS this semester", (iii) 7.8, (iv) "The average CGPA of EE students is 7.8".

Solution

(i) data, (iii) data: raw values. (ii) and (iv) are information: each is computed from many raw values and answers a question.

Example 2 Medium

A bank keeps savings accounts in one file and loans in another, each with the customer's address. A customer moves house and the savings file is updated. Name the two problems this shows.

Solution

Redundancy (address stored twice) and, after the update, inconsistency (two different addresses for one customer).

Example 3 GATE

Money is transferred: ₹500 is subtracted from account X, then the system crashes before ₹500 is added to account Y. Which file-processing problem is this, and what property would have prevented it?

Solution

An atomicity problem. The transfer is one logical task made of two steps; it must be all or nothing. With atomicity, the crash would undo the subtraction, so no money disappears.

8 · Connect the Dots

This lesson listed what goes wrong when every program owns its own file. Next lesson: the software that fixes these eight problems, the DBMS, what exactly it does, and the people who use it.

9 · Self-Test

GATE format. Try every question before opening the vault.

Q1 · MCQ · 1 mark(s) — Data vs information

Which of these is information rather than data?

1. (A) C1
2. (B) The CS department has the highest average CGPA
3. (C) 9.1
4. (D) Asha

Q2 · MCQ · 1 mark(s) — Problems

Two clerks read "1 seat left" at the same moment and both confirm a booking. Which problem is this?

1. (A) Redundancy
2. (B) Data isolation
3. (C) Atomicity problem
4. (D) Concurrent-access anomaly

Q3 · MSQ · 2 mark(s) — Problems

A college stores the same student's address in three different files. Which problems can result directly from this?

1. (A) Inconsistency
2. (B) Security problems
3. (C) Redundancy
4. (D) Wasted storage

Q4 · MCQ · 1 mark(s) — Problems

A new rule says CGPA must be between 0 and 10. In a file-processing system, why is this hard to enforce?

1. (A) The rule must be added to every program that writes CGPA
2. (B) Files cannot store decimal numbers
3. (C) The rule makes queries slower
4. (D) Files cannot be shared between programs

Q5 · NAT · 1 mark(s) — Counting copies

A student's phone number is stored in 5 separate office files. The student updates it at 2 offices. How many copies are now out of date?

Numerical answer: ________

11 · Concept Ledger

Unlocked in this lesson. From here on, these terms may be used.

datainformationdatabasefile-processing systemredundancyinconsistencydata isolationintegrity ruleatomicity (all or nothing)concurrent accesssecurity