Database Management System (AD-402) Unit 1 Notes

How unit 1 is examined

This unit covers file system versus database, the three-level DBMS architecture, schemas, the DBA, and the E-R model with its extensions and the three classic data models. The marks sit in architecture, schemas and instances, the DBA, and E-R features.

Database approach v/s Traditional file accessing approach

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Low weight</span>

Definition. Data is raw facts and figures; a database is an organised collection of related data; a DBMS is software to create, manage and query the database. <mark>In the database approach one shared, centrally controlled store serves all applications, whereas in the file approach each application keeps its own files.</mark>

Basis	File approach	Database approach
Redundancy	High, each program has its own copy	Controlled, one shared copy
Sharing	Poor, files tied to one program	Many users share concurrently
Integrity	Rules coded in every program	Enforced centrally by constraints
Security	Only OS file permissions	User-wise authorisation
Independence	Program depends on file format	Data independent of programs

Asked: [7 marks] (Jun 2025) Write the differences between Database approach v/s Traditional file accessing approach. Asked: [7 marks] (Jun 2025) Define: i) Data ii) Data base iii) Data base management.

Advantages of database systems

Definition. A DBMS lets many users store, share and protect one integrated collection of data.

Key points.

Redundancy is controlled because data is stored once, which keeps copies consistent and saves space.
Data is shared among many users and applications, and integrity constraints keep it correct.
Security is enforced through authorisation, and concurrent access is made safe by concurrency control.
Backup and recovery restore the database after a failure.
Data independence and standard tools cut development time.

Asked: [7 marks] (Jun 2023) List and explain the advantages of DBMS.

Data models

Definition. A data model is a collection of concepts for describing the structure of data, its relationships and its constraints.

Key points.

Conceptual (high-level) models such as E-R are close to how users see data.
Representational (logical) models such as relational, network and hierarchical are used by DBMSs.
Physical models describe files, indexes and storage.

Schemas and instances

Definition. A schema is the overall description (design) of the database and changes rarely; an instance is the data actually stored at a particular moment and changes constantly. <mark>Schema is the blueprint of the database; instance is a snapshot of its contents.</mark>

Basis	Conceptual schema	Logical schema	Physical schema
Describes	Entities and relationships for the whole enterprise	Tables, columns, keys, types	Files, indexes, storage, access paths
Abstraction	Highest, no DBMS detail	Middle, tied to a data model	Lowest, hardware level
Audience	Designers, business users	Developers, DBA	DBA, system engineers
Independence	Independent of DBMS	Independent of storage	Changed without touching logical schema
Example	STUDENT enrolls in COURSE	STUDENT(Roll, Name) table	B-tree index on Roll

Key points.

Schema is fixed at design time through DDL, while the instance changes on every insert, update or delete.
A schema is also called the intension and an instance the extension of the database.
The three-level architecture has an external (view) schema, a conceptual schema and an internal (physical) schema.
The DBMS checks every instance against the schema, so a valid instance always obeys the schema.
Changing the schema is costly, and changing an instance is routine.

Example. Schema: STUDENT(Roll, Name, Branch). Instance: (101, Asha, CS), (102, Ravi, IT) at today's date; tomorrow a new row makes a new instance of the same schema.

Answer frame. For the comparison, open with the three definitions; draw the table above; give one example per level; close by stating the differences in abstraction and independence. For the short note, define schema and instance, give the STUDENT example, name the three schema levels and close with the blueprint versus snapshot line.

Asked: [14 marks] (Jun 2025) Write a short note on any two: a) Schemas and Instances b) Triggers c) Query Optimization d) Serializability. Asked: [7 marks] (Jun 2024) Differentiate between conceptual, logical, and physical schemas.

Data independence

Definition. Data independence is the ability to change the schema at one level without changing the schema at the next higher level.

Key points.

Logical data independence lets the conceptual schema change (add a field) without changing external views or programs.
Physical data independence lets the internal schema change (new index, file organisation) without changing the conceptual schema.
Mappings between levels absorb the changes.
Logical independence is harder to achieve than physical.

Data Base Language and interfaces

Definition. Database languages are the statements users use to define and manipulate data.

Key points.

DDL (CREATE, ALTER, DROP) defines schemas; DML (SELECT, INSERT, UPDATE, DELETE) retrieves and modifies data; DCL (GRANT, REVOKE) controls access.
DML is procedural (user says how) or non-procedural (user says what, as in SQL).
Interfaces include menu-based, forms-based, graphical, natural-language, command-line and programmer (embedded SQL, API) interfaces.

Overall Database Structure

Definition. The architecture of a DBMS is the three-level ANSI/SPARC structure of external, conceptual and internal levels together with its components: query processor, storage manager and transaction manager. <mark>The three-level architecture separates the users' views from the logical design and from physical storage.</mark>

Diagram. <figure class="ds-fig" style="margin:1.4rem 0;overflow-x:auto"><svg xmlns="http://www.w3.org/2000/svg" id="dsfig-u1-01" viewBox="0 0 467 415.4" width="467" height="415.4" role="img" aria-label="DBMS architecture. Usr users, Ext external level (views), Con conceptual level, Int internal level, QP query processor, SM storage manager, DB stored database."><style>#dsfig-u1-01 .e{stroke:#454C5A;stroke-width:1.4;fill:none}#dsfig-u1-01 .e.hi{stroke:#2340B8;stroke-width:2.6}#dsfig-u1-01 .n{fill:#FFFFFF;stroke:#16181D;stroke-width:1.4}#dsfig-u1-01 .n.hi{fill:#E3E9FC;stroke:#2340B8;stroke-width:2.2}#dsfig-u1-01 .n.rb-b{fill:#16181D;stroke:#16181D}#dsfig-u1-01 .n.rb-r{fill:#BD3227;stroke:#BD3227}#dsfig-u1-01 text{font-family:"JetBrains Mono",ui-monospace,Menlo,Consolas,monospace;font-size:13px}#dsfig-u1-01 .t{fill:#16181D;font-weight:500}#dsfig-u1-01 .t.inv{fill:#FFFFFF;font-weight:700}#dsfig-u1-01 .kd{stroke:#16181D;stroke-width:1.2}#dsfig-u1-01 .dot{fill:#16181D}#dsfig-u1-01 .ann{fill:#2340B8;font-size:11px;font-weight:700}#dsfig-u1-01 .lbl{fill:#6F7787;font-family:system-ui,-apple-system,sans-serif;font-size:12px;font-weight:700}#dsfig-u1-01 .ptr{fill:#2340B8;font-size:12px;font-weight:700}#dsfig-u1-01 .ah{fill:#454C5A}#dsfig-u1-01 .ah.hi{fill:#2340B8}#dsfig-u1-01 .wl rect{fill:#FFFFFF;stroke:#DCE0E7}#dsfig-u1-01 .wl .t{font-size:12px;font-weight:700}#dsfig-u1-01 .wl.hi rect{fill:#2340B8;stroke:#2340B8}#dsfig-u1-01 .wl.hi .t{fill:#FFFFFF}html.dark #dsfig-u1-01 .e{stroke:#B1B7C3}html.dark #dsfig-u1-01 .e.hi{stroke:#8FA3FF}html.dark #dsfig-u1-01 .n{fill:#161920;stroke:#E6E8ED}html.dark #dsfig-u1-01 .n.hi{fill:#1E2748;stroke:#8FA3FF}html.dark #dsfig-u1-01 .n.rb-b{fill:#E6E8ED;stroke:#E6E8ED}html.dark #dsfig-u1-01 .n.rb-r{fill:#FF7E71;stroke:#FF7E71}html.dark #dsfig-u1-01 .t{fill:#E6E8ED}html.dark #dsfig-u1-01 .t.inv{fill:#0F1115}html.dark #dsfig-u1-01 .kd{stroke:#E6E8ED}html.dark #dsfig-u1-01 .dot{fill:#E6E8ED}html.dark #dsfig-u1-01 .ann{fill:#8FA3FF}html.dark #dsfig-u1-01 .lbl{fill:#858D9C}html.dark #dsfig-u1-01 .ptr{fill:#8FA3FF}html.dark #dsfig-u1-01 .ah{fill:#B1B7C3}html.dark #dsfig-u1-01 .ah.hi{fill:#8FA3FF}html.dark #dsfig-u1-01 .wl rect{fill:#161920;stroke:#2A2E37}html.dark #dsfig-u1-01 .wl.hi rect{fill:#8FA3FF;stroke:#8FA3FF}html.dark #dsfig-u1-01 .wl.hi .t{fill:#0F1115}</style><defs><marker id="ah1" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="ah" d="M0,1 L9,5 L0,9 z"/></marker><marker id="ahh1" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="ah hi" d="M0,1 L9,5 L0,9 z"/></marker></defs><path class="e" d="M59,40 L191,40" marker-end="url(#ah1)"/><path class="e" d="M212,59 L212,130.8" marker-end="url(#ah1)"/><path class="e" d="M212,170.8 L212,242.6" marker-end="url(#ah1)"/><path class="e" d="M212,282.6 L212,354.4" marker-end="url(#ah1)"/><path class="e" d="M58.8,42.5 L406.2,88.8" marker-end="url(#ah1)"/><path class="e" d="M427,110.6 L427,242.6" marker-end="url(#ah1)"/><path class="e" d="M410.1,272.4 L230.6,365.7" marker-end="url(#ah1)"/><g class="wl"><rect x="191.6" y="86.9" width="40.8" height="18" rx="9"/><text class="t" x="212" y="95.9" dy=".35em" text-anchor="middle">map1</text></g><g class="wl"><rect x="191.6" y="198.7" width="40.8" height="18" rx="9"/><text class="t" x="212" y="207.7" dy=".35em" text-anchor="middle">map2</text></g><circle class="n" cx="40" cy="40" r="18"/><text class="t" x="40" y="40" dy=".35em" text-anchor="middle">Usr</text><circle class="n" cx="212" cy="40" r="18"/><text class="t" x="212" y="40" dy=".35em" text-anchor="middle">Ext</text><circle class="n" cx="212" cy="151.8" r="18"/><text class="t" x="212" y="151.8" dy=".35em" text-anchor="middle">Con</text><circle class="n" cx="212" cy="263.6" r="18"/><text class="t" x="212" y="263.6" dy=".35em" text-anchor="middle">Int</text><circle class="n" cx="212" cy="375.4" r="18"/><text class="t" x="212" y="375.4" dy=".35em" text-anchor="middle">DB</text><circle class="n" cx="427" cy="91.6" r="18"/><text class="t" x="427" y="91.6" dy=".35em" text-anchor="middle">QP</text><circle class="n" cx="427" cy="263.6" r="18"/><text class="t" x="427" y="263.6" dy=".35em" text-anchor="middle">SM</text></svg><figcaption style="font-size:.82em;opacity:.72;margin-top:.45rem">DBMS architecture. Usr users, Ext external level (views), Con conceptual level, Int internal level, QP query processor, SM storage manager, DB stored database.</figcaption></figure>

Key points.

The external level gives each user group its own view of only the data it needs, hiding the rest.
The conceptual level describes the whole database (entities, relationships, constraints) for the community, independent of storage.
The internal level describes physical storage: files, indexes, record formats and access paths.
Mappings (external/conceptual and conceptual/internal) translate requests between levels and give logical and physical data independence.
The query processor contains the DDL interpreter, DML compiler and query evaluation engine; it turns queries into low-level instructions.
The storage manager (buffer, file and authorisation manager) stores, retrieves and updates data on disk; the transaction manager keeps transactions atomic and consistent.
Users are naive users, application programmers, sophisticated users and the DBA, each using a different interface.

Answer frame. Open with the definition of three-level architecture; draw the figure above with full names; develop points 1-4, then 5-6 for components, then 7; close with the line about data independence.

Asked: [7 marks] (Jun 2023, Jun 2024, Jun 2026) Explain in brief architecture of DBMS with a neat sketch. / Describe the architecture of a typical database system. / Discuss the architecture of DBMS with proper diagram.

Functions of DBA and designer

Definition. The Database Administrator (DBA) is the person or team with central control over the database and the DBMS. <mark>The DBA defines, secures, backs up and tunes the database, and the designer decides what data it holds and how it is structured.</mark>

Key points.

Schema definition: the DBA creates the original schema and later modifies it using DDL.
Security and authorisation: the DBA grants and revokes access rights to users.
Backup and recovery: the DBA takes periodic backups and restores the database after failure.
Performance tuning: the DBA creates indexes, reorganises storage and monitors response time.
Integrity: the DBA specifies constraints and monitors data quality.
Types of DBA are the system DBA (installs, configures, upgrades), the database architect or designer DBA (designs schema), the application DBA (supports applications and tuning) and the data warehouse or security DBA.
Database designers identify the data, choose structures and design views for each user group, in agreement with users.

Answer frame. Open with what a DBA is; list the duties 1-5 with one line each; add the types and the designer's role for the "types" question; close with the DBA's importance for security and maintenance.

Asked: [7 marks] (Jun 2025) What are the responsibilities of DBA? Explain in detail. Asked: [7 marks] (Jun 2026) What is Database Administrator (DBA) and also write type of Database Administrator.

ER data model: Entities and attributes

Definition. The E-R model describes data as entities, their attributes and the relationships among them. <mark>An entity is a distinguishable real-world object, an attribute is a property of it, and a relationship associates entities.</mark>

Diagram. <figure class="ds-fig" style="margin:1.4rem 0;overflow-x:auto"><svg xmlns="http://www.w3.org/2000/svg" id="dsfig-u1-02" viewBox="0 0 542.8 191.8" width="542.8" height="191.8" role="img" aria-label="E-R diagram. Std STUDENT (key Roll), Enr Enrolls relationship, Crs COURSE (key CID), Titl Title. Many students enrol in many courses (M:N)."><style>#dsfig-u1-02 .e{stroke:#454C5A;stroke-width:1.4;fill:none}#dsfig-u1-02 .e.hi{stroke:#2340B8;stroke-width:2.6}#dsfig-u1-02 .n{fill:#FFFFFF;stroke:#16181D;stroke-width:1.4}#dsfig-u1-02 .n.hi{fill:#E3E9FC;stroke:#2340B8;stroke-width:2.2}#dsfig-u1-02 .n.rb-b{fill:#16181D;stroke:#16181D}#dsfig-u1-02 .n.rb-r{fill:#BD3227;stroke:#BD3227}#dsfig-u1-02 text{font-family:"JetBrains Mono",ui-monospace,Menlo,Consolas,monospace;font-size:13px}#dsfig-u1-02 .t{fill:#16181D;font-weight:500}#dsfig-u1-02 .t.inv{fill:#FFFFFF;font-weight:700}#dsfig-u1-02 .kd{stroke:#16181D;stroke-width:1.2}#dsfig-u1-02 .dot{fill:#16181D}#dsfig-u1-02 .ann{fill:#2340B8;font-size:11px;font-weight:700}#dsfig-u1-02 .lbl{fill:#6F7787;font-family:system-ui,-apple-system,sans-serif;font-size:12px;font-weight:700}#dsfig-u1-02 .ptr{fill:#2340B8;font-size:12px;font-weight:700}#dsfig-u1-02 .ah{fill:#454C5A}#dsfig-u1-02 .ah.hi{fill:#2340B8}#dsfig-u1-02 .wl rect{fill:#FFFFFF;stroke:#DCE0E7}#dsfig-u1-02 .wl .t{font-size:12px;font-weight:700}#dsfig-u1-02 .wl.hi rect{fill:#2340B8;stroke:#2340B8}#dsfig-u1-02 .wl.hi .t{fill:#FFFFFF}html.dark #dsfig-u1-02 .e{stroke:#B1B7C3}html.dark #dsfig-u1-02 .e.hi{stroke:#8FA3FF}html.dark #dsfig-u1-02 .n{fill:#161920;stroke:#E6E8ED}html.dark #dsfig-u1-02 .n.hi{fill:#1E2748;stroke:#8FA3FF}html.dark #dsfig-u1-02 .n.rb-b{fill:#E6E8ED;stroke:#E6E8ED}html.dark #dsfig-u1-02 .n.rb-r{fill:#FF7E71;stroke:#FF7E71}html.dark #dsfig-u1-02 .t{fill:#E6E8ED}html.dark #dsfig-u1-02 .t.inv{fill:#0F1115}html.dark #dsfig-u1-02 .kd{stroke:#E6E8ED}html.dark #dsfig-u1-02 .dot{fill:#E6E8ED}html.dark #dsfig-u1-02 .ann{fill:#8FA3FF}html.dark #dsfig-u1-02 .lbl{fill:#858D9C}html.dark #dsfig-u1-02 .ptr{fill:#8FA3FF}html.dark #dsfig-u1-02 .ah{fill:#B1B7C3}html.dark #dsfig-u1-02 .ah.hi{fill:#8FA3FF}html.dark #dsfig-u1-02 .wl rect{fill:#161920;stroke:#2A2E37}html.dark #dsfig-u1-02 .wl.hi rect{fill:#8FA3FF;stroke:#8FA3FF}html.dark #dsfig-u1-02 .wl.hi .t{fill:#0F1115}</style><defs><marker id="ah2" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="ah" d="M0,1 L9,5 L0,9 z"/></marker><marker id="ahh2" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="ah hi" d="M0,1 L9,5 L0,9 z"/></marker></defs><path class="e" d="M83.6,134.5 L50.9,63.6"/><path class="e" d="M100.6,135.1 L139.5,62.9"/><path class="e" d="M110.6,151.8 L244.6,151.8"/><path class="e" d="M282.6,151.8 L416.6,151.8"/><path class="e" d="M427.6,134.5 L392,57.3"/><path class="e" d="M444.6,135.1 L483.5,62.9"/><g class="wl"><rect x="168" y="142.8" width="19.2" height="18" rx="9"/><text class="t" x="177.6" y="151.8" dy=".35em" text-anchor="middle">M</text></g><g class="wl"><rect x="340" y="142.8" width="19.2" height="18" rx="9"/><text class="t" x="349.6" y="151.8" dy=".35em" text-anchor="middle">N</text></g><rect class="n" x="15" y="25" width="50" height="30" rx="15"/><text class="t" x="40" y="40" dy=".35em" text-anchor="middle">Roll</text><rect class="n" x="126.8" y="25" width="50" height="30" rx="15"/><text class="t" x="151.8" y="40" dy=".35em" text-anchor="middle">Name</text><circle class="n" cx="91.6" cy="151.8" r="18"/><text class="t" x="91.6" y="151.8" dy=".35em" text-anchor="middle">Std</text><circle class="n" cx="263.6" cy="151.8" r="18"/><text class="t" x="263.6" y="151.8" dy=".35em" text-anchor="middle">Enr</text><circle class="n" cx="435.6" cy="151.8" r="18"/><text class="t" x="435.6" y="151.8" dy=".35em" text-anchor="middle">Crs</text><circle class="n" cx="384" cy="40" r="18"/><text class="t" x="384" y="40" dy=".35em" text-anchor="middle">CID</text><rect class="n" x="470.8" y="25" width="50" height="30" rx="15"/><text class="t" x="495.8" y="40" dy=".35em" text-anchor="middle">Titl</text></svg><figcaption style="font-size:.82em;opacity:.72;margin-top:.45rem">E-R diagram. Std STUDENT (key Roll), Enr Enrolls relationship, Crs COURSE (key CID), Titl Title. Many students enrol in many courses (M:N).</figcaption></figure>

Key points.

An entity set is a collection of similar entities, such as all students; a relationship set associates entity sets.
Attributes may be simple or composite, single-valued or multivalued, stored or derived.
A primary key uniquely identifies each entity; a foreign key is an attribute that refers to the primary key of another table.
Mapping cardinality is one-to-one, one-to-many, many-to-one or many-to-many.
A weak entity has no key of its own and depends on a strong entity; generalization, specialization and aggregation extend the model.
Rectangles are entities, ellipses attributes, diamonds relationships, and double lines mark total participation.

Answer frame. Open with the E-R definition; draw the figure above; develop points 1-5; close with the note that E-R diagrams convert directly into tables.

Asked: [7 marks] (Jun 2023, Jun 2026) State and explain various features of E-R Models. / Explain entity, attributes, entity sets and relationship types with examples and identify primary and foreign keys.

Entity types

Definition. A strong entity has its own primary key; a weak entity does not and depends on an owner entity.

Key points.

A strong entity such as STUDENT is drawn as a single rectangle.
A weak entity such as DEPENDENT is drawn as a double rectangle, with a partial (discriminator) key drawn dashed-underlined.
A weak entity's key is the owner's key plus its discriminator.
It is linked through an identifying relationship, drawn as a double diamond.

Defining the E-R diagram

Definition. An E-R diagram is the graphical picture of entities, attributes and relationships of an enterprise.

Key points.

Steps: identify entity sets, identify relationships, add attributes and keys, then mark cardinalities and participation.
Rectangles are entities, ellipses attributes, diamonds relationships and lines connect them.
The primary key attribute is underlined.
The diagram is the conceptual design that is later mapped to tables.

Concept of Generalization

Definition. Generalization is a bottom-up process that combines lower-level entity sets sharing common attributes into a higher-level superclass. <mark>Generalization is bottom-up, specialization is top-down, and aggregation treats a relationship as a whole-part higher-level entity.</mark>

Key points.

Example: CAR and TRUCK generalize into VEHICLE, which holds their common attributes.
Specialization is the reverse: VEHICLE is split top-down into CAR and TRUCK, each with its own attributes.
Aggregation treats a relationship set as a single entity so it can join another relationship (has-a).
Lower-level entities inherit the attributes of the higher-level one, drawn with an ISA triangle.

Asked: [7 marks] (Jun 2026) What do mean by generalization, aggregation and specialization.

Aggregation

Definition. Aggregation is an abstraction in which a relationship set is treated as a higher-level entity so it can take part in another relationship.

Key points.

It models a whole-part or "has-a" relationship.
Example: EMPLOYEE works on PROJECT is aggregated and then related to MACHINERY, which records the machinery used.
It avoids redundant relationships.

Specialization

Definition. Specialization is a top-down process of dividing an entity set into subgroups with distinguishing attributes.

Key points.

Example: EMPLOYEE specializes into ENGINEER and MANAGER.
Subclasses inherit the attributes of the superclass and add their own.
It is drawn with an ISA triangle and may be disjoint or overlapping, total or partial.

Transforming ER diagram into the tables

Definition. Each E-R construct is mapped to a relation to obtain the relational schema.

Key points.

A strong entity becomes a table with its attributes, and its key is the primary key.
A weak entity becomes a table containing the owner's primary key as foreign key plus its discriminator.
A many-to-many relationship becomes a new table with both primary keys as a composite key; a one-to-many one puts a foreign key on the many side.
A multivalued attribute becomes a separate table; a composite attribute is split into components.

Various other data models object oriented data Model

Definition. The object-oriented data model stores data as objects that combine attributes and methods, grouped into classes.

Key points.

It supports encapsulation, inheritance, object identity and complex types.
Objects refer to one another through object identifiers (OIDs).
It suits multimedia, CAD and engineering applications, but is complex and lacks a standard.

Network data model

Definition. The network data model (CODASYL) organises records as nodes connected by links in a graph structure.

Key points.

A record can have many parents, so many-to-many relationships are possible using set types.
Data is retrieved by navigating pointers, which is fast for known paths.
The structure is complex and not flexible when the design changes.

Relational data model

Definition. The relational model, proposed by E. F. Codd, stores data as relations (tables) of rows and columns.

Key points.

Rows are tuples, columns are attributes, and each attribute takes values from a domain.
Keys and foreign keys link tables, with no physical pointers.
It is queried with declarative languages such as SQL and relational algebra, with a strong mathematical base.

Comparison between the three types of models

Definition. The object-oriented, network and relational models differ in how they store data and link records.

Basis	Object-oriented	Network	Relational
Structure	Objects and classes	Records linked by pointers	Tables of rows
Strength	Complex data, reuse	Fast known paths	Simple, flexible, SQL
Limitation	Complex, no standard	Rigid, hard to change	Weak on complex types
Suits	CAD, multimedia	Telecom, banking legacy	Business, ERP, web

Asked: [7 marks] (Jun 2024) Discuss the suitability of each, object-oriented, network and relational data models for different types of applications.

Last-minute revision

Data is raw facts; database is organised related data; DBMS is software to manage it.
Database approach controls redundancy, shares data and enforces integrity centrally.
Schema is the design and rarely changes; instance is the data at a moment.
Three levels: external, conceptual, internal, joined by two mappings.
Logical independence protects external views; physical independence protects the conceptual schema.
DDL defines, DML manipulates, DCL controls access.
DBA duties: schema, security, backup, performance, integrity.
Weak entity has no key of its own; it uses a double rectangle.
Generalization is bottom-up, specialization top-down, aggregation is has-a.
M:N relationship becomes a separate table with a composite key.

Memory hooks

ESC-IM: External, Conceptual (and) Internal with Mappings.
Schema is the Skeleton, instance is the Snapshot.
DBA duties: SSBP, Schema, Security, Backup, Performance.
Generalize goes Up, specialize goes Down.

Coverage checklist

Database approach v/s Traditional file accessing approach: file versus database, definitions of data, database, DBMS.
Advantages, of database systems: advantages of DBMS.
Data models: types of data models.
Schemas and instances: conceptual, logical, physical schemas; short note on schemas and instances.
Data independence: logical and physical independence.
Data Base Language and interfaces: DDL, DML, interfaces.
Overall Database Structure: DBMS architecture with sketch.
Functions of DBA and designer: DBA responsibilities and types.
ER data model: Entitles and attributes: features of E-R model.
Entity types: strong and weak entities.
Defining the E-R diagram: notation and steps.
Concept of Generalization: generalization, aggregation, specialization.
Aggregation: has-a abstraction.
Specialization: top-down design.
transforming ER diagram into the tables: mapping rules.
Various other data models object oriented data Model: object-oriented model.
Network data model: CODASYL model.
Relational data model: Codd tables.
Comparison between the three types of models: suitability of models.

Account

Database Management System (AD-402) - Unit 1 Short Notes

How unit 1 is examined

Database approach v/s Traditional file accessing approach

Advantages of database systems

Data models

Schemas and instances

Data independence

Data Base Language and interfaces

Overall Database Structure

Functions of DBA and designer

ER data model: Entities and attributes

Entity types

Defining the E-R diagram

Concept of Generalization

Aggregation

Specialization

Transforming ER diagram into the tables

Various other data models object oriented data Model

Network data model

Relational data model

Comparison between the three types of models

Last-minute revision

Memory hooks

Coverage checklist