A · Compressed recap
A database is related data; a DBMS is the software that defines, builds, queries, updates and shares it; together they form a database system. The DBMS fixes the eight problems of file-processing systems (RIDIIACS: redundancy, inconsistency, difficult access, isolation, integrity, atomicity, concurrency, security). It is self-describing: metadata lives in the catalog. DDL defines structure, DML reads and changes data. Users: DBA, designers, end users (naive, casual, sophisticated, stand-alone), application programmers.
The schema (intension) describes; the instance (state) is the data now. Three levels: many external views, one conceptual schema, one internal schema, joined by two mappings. Physical independence: internal changes do not touch the conceptual schema. Logical independence (harder): conceptual changes do not touch views. Data models: conceptual (ER) → representational (relational) → physical; design runs requirements → ER → tables → normalisation → physical design.
B · Merged rule card
0.1.1 Data vs information; plain files and their problems
- Data = raw facts; information = processed data that answers a question.
- File-processing system: each program owns its own files.
- Its problems (RIDIIACS): Redundancy, Inconsistency, Difficult access, Isolation, Integrity, Atomicity, Concurrency, Security.
- Redundancy = same fact stored more than once; inconsistency = copies disagree.
- Atomic = all or nothing; concurrent = at the same time.
0.1.2 What a DBMS is and what it does; its users (end users, application programmers, DBA)
- Database = related data; DBMS = software to define, build, query, update and share it; database system = both.
- DBMS jobs: definition, querying, updating, concurrency control, recovery, security, integrity checks.
- Metadata (data about data) lives in the catalog: the database is self-describing.
- DDL defines structure; DML reads and changes data.
- Users: DBA (access, storage, performance, backup), designers, end users (naive, casual, sophisticated, stand-alone), application programmers.
- Costs of a DBMS: money, training, overhead.
0.1.3 Schema vs instance; three-schema architecture; logical and physical data independence
- Schema = description (intension), rarely changes. Instance = data at a moment (state, extension), changes constantly.
- Three levels: external (many views) → conceptual (one, whole database, what) → internal (one, storage, how).
- Two mappings: external–conceptual and conceptual–internal.
- Physical data independence: internal change, conceptual unchanged. Easier.
- Logical data independence: conceptual change, views/apps unchanged. Harder.
0.1.4 Data models: conceptual vs logical vs physical; where ER and relational fit
- Data model = concepts for describing data structure, connections, rules (and operations).
- Conceptual (ER) → representational/logical (relational) → physical (files, indexes).
- Design process: requirements → conceptual (ER) → logical (tables) → refinement (normalisation) → physical.
- DBMSs implement the relational model; ER diagrams are converted to tables.
C · Interleaved GATE-style questions
Q1 · MCQ · 1 mark(s) — File problems
A program crashes after removing a fee from "pending" but before adding it to "paid". This is:
- (A) an integrity problem
- (B) data isolation
- (C) an atomicity problem
- (D) a concurrency problem
Q2 · MCQ · 1 mark(s) — Users
Who decides access rights and plans backup and recovery?
- (A) Database designer
- (B) DBA
- (C) Sophisticated user
- (D) Application programmer
Q3 · MSQ · 2 mark(s) — Independence
Which changes are absorbed by physical data independence?
- (A) Creating an index on dept
- (B) Changing the order in which records are stored
- (C) Moving data to faster disks
- (D) Adding a field "email" to STUDENT
Q4 · MCQ · 1 mark(s) — Schema vs instance
Which changes most often?
- (A) Internal schema
- (B) External schema
- (C) Conceptual schema
- (D) Database instance
Q5 · MCQ · 2 mark(s) — Levels
A new field is added to the conceptual schema and the exam-cell view, which does not use it, keeps working unchanged. Which mapping had to be updated, and which independence is shown?
- (A) conceptual–internal; logical
- (B) external–conceptual; physical
- (C) external–conceptual; logical
- (D) conceptual–internal; physical
Q6 · MCQ · 1 mark(s) — Data models
Which pairing is correct?
- (A) Relational model – representational
- (B) ER model – physical
- (C) Index – conceptual
- (D) Relational model – conceptual only, never implemented
Q7 · NAT · 1 mark(s) — Counting
Four offices each store the same student's address. How many redundant copies are there (copies beyond the first)?
Numerical answer: ________
Q8 · MSQ · 2 mark(s) — DBMS
Which are disadvantages of using a DBMS?
- (A) Overhead for features a small application does not need
- (B) Inability to run more than one user at a time
- (C) Cost of software and training
- (D) Higher data redundancy than files
D · Answer Vault
Reveal answers when you’re ready
Q1 Answer: (C) · 1 mark(s)
One task stopped halfway.
- (A) is wrong: No declared rule was broken.
- (B) is wrong: Isolation is scattered formats.
- (D) is wrong: Only one user involved.
Re-read: Lesson 0.1.1 — Data vs information; plain files and their problems
Q2 Answer: (B) · 1 mark(s)
These are DBA duties.
- (A) is wrong: Designs structure.
- (C) is wrong: Writes complex queries.
- (D) is wrong: Writes programs.
Re-read: Lesson 0.1.2 — What a DBMS is and what it does; its users (end users, application programmers, DBA)
Q3 Answer: (A) (B) (C) · 2 mark(s)
All three change only the internal schema. Adding a field changes the conceptual schema.
- (D) is wrong: That needs logical data independence.
Re-read: Lesson 0.1.3 — Schema vs instance; three-schema architecture; logical and physical data independence
Q4 Answer: (D) · 1 mark(s)
Every insert, update or delete changes the instance.
- (A) is wrong: Changes rarely.
- (B) is wrong: Changes rarely.
- (C) is wrong: Changes rarely.
Re-read: Lesson 0.1.3 — Schema vs instance; three-schema architecture; logical and physical data independence
Q5 Answer: (C) · 2 mark(s)
The conceptual schema changed; the view was protected by updating the external–conceptual mapping. That is logical data independence.
- (A) is wrong: Wrong mapping.
- (B) is wrong: Wrong independence name.
- (D) is wrong: Physical independence is about internal changes.
Re-read: Lesson 0.1.3 — Schema vs instance; three-schema architecture; logical and physical data independence
Q6 Answer: (A) · 1 mark(s)
The relational model is representational and implemented by DBMSs.
- (B) is wrong: ER is conceptual.
- (C) is wrong: Indexes are physical.
- (D) is wrong: It is implemented.
Re-read: Lesson 0.1.4 — Data models: conceptual vs logical vs physical; where ER and relational fit
Q7 Answer: 3 · 1 mark(s)
4 copies, 1 needed: 3 redundant.
Re-read: Lesson 0.1.1 — Data vs information; plain files and their problems
Q8 Answer: (A) (C) · 2 mark(s)
Cost and overhead are the standard drawbacks.
- (B) is wrong: A DBMS supports many users.
- (D) is wrong: A DBMS reduces redundancy.
Re-read: Lesson 0.1.2 — What a DBMS is and what it does; its users (end users, application programmers, DBA)