Venkatesh Vinayakarao (Vv)

RELATIONAL Database

Management System (RDBMS)

Concepts and SQl

Venkatesh Vinayakaraovenkateshv@cmi.ac.in

http://vvtesh.co.in

Chennai Mathematical Institute

The primary goal of a DBMS is to provide a way to store and retrieve database information that isboth convenient and efficient. - Silberschatz, Korth and Sudarshan.

A database-management system (DBMS) is a collection of:

1. interrelated data and 2. a set of programs to access those data.

The collection of data is usually referred to as database.

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Why files are insufficient to store data?

Why files are insufficient?

• Major disadvantages of using files to store and retrieve data• Data redundancy and inconsistency

• Classic example – Address book. Same phone number and address may repeat and may also be inconsistent

• Difficulty in access• Unrestricted file format implies custom programs need to be

written• Data integrity (Atomicity of transactions)

• Assume having a debit ledger and credit ledger!

• Backups• Concurrent access and related anomalies• Security

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An Architecture for a Database Management System (DBMS)

How is the data stored?

Description of the data and its relationships.

Architecture

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Data Models

• We are interested in understanding, describing and analyzing several aspects of data such as:• Data • Data relationships• Data semantics• Data constraints

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A data model captures these aspects.

Several models exist: Relational, Entity-

Relationship, Object Oriented, etc.

Schema

• Logical Schema – the overall logical structure of the database • Example: Set of customers and accounts in a bank and

the relationship between them

• Physical schema– the overall physical structure of the database

Physical Data IndependenceThe ability to modify the physical schema without

changing the logical schema

History

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1950

Tapes and punched cards – Sequential

data access

1960

Direct access with hard disks. Codd introduces

relational data model. UC Berkeley builds Ingres.

1980

SQL becomes a standard.

Parallel, Obj Oriented and Distributed DBMS are built.

1990

multi-terabyte data warehouses,

web commerce

2000

XML Standards emerge.Now

Big Data, NoSQL DB.

Course Dynamics

Course Text

https://www.db-book.com/db6/index.html

Assessment

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Component Weight

Assignments (2 * 10%) 20%

Exam 30%

Course Plan*

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Topics Text Book Reference

Introduction to RDBMS Chapters 1, 2

SQL Chapters 3, 4

Relational Model Relational Algebra

Chapters 6

Relational Database Design Functional Dependencies, Normal Forms, Keys, Decomposition

Chapters 7, 8

Data Storage and Querying Storage, Indexing Structures

Chapters 10, 11

Transaction ManagementACID Properties, Transactions, Concurrency control, Serialization

Chapter 14

* Tentative

Acknowledgment

• Slide contents are borrowed from the official website of the course text. For the authors’ original version of slides, visit: • https://www.db-book.com/db6/slide-dir/index.html

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Introduction to RDBMS

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Relational Model

• All the data is stored in various tables.

• Example of tabular data in the relational model

A Sample Relational Database

Exercise: Describe these two tables in your own words (in two to three

sentences each).

Data Definition Language (DDL)

• Specification notation for defining the database schema

• DDL compiler generates a set of table templates stored in a data dictionary

• Data dictionary contains metadata (i.e., data about data)• Database schema

• Integrity constraints• Primary key (ID uniquely identifies instructors)

• Authorization

Defining Instructor Relation

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Data Manipulation Language (DML)• Language for accessing and manipulating the data

organized by the appropriate data model• DML also known as query language

• Two classes of languages • Pure – used for proving properties about computational

power and for optimization• Relational Algebra

• Tuple relational calculus

• Domain relational calculus

• Commercial – used in commercial systems• SQL is the most widely used commercial language

SQL

• The most widely used commercial language

• Application programs generally access databases through one of• Language extensions to allow embedded SQL

• Application program interface (e.g., ODBC/JDBC) which allow SQL queries to be sent to a database

Sample SQL statements

select name from instructor

update instructorset salary = salary * 1.03where salary > 100000;

Database Design

• The process of designing the general structure of the database:• Logical Design – Deciding on the database schema.

Database design requires that we find a “good” collection of relation schemas.• Business decision – What attributes should we record in the

database?

• Computer Science decision – What relation schemas should we have and how should the attributes be distributed among the various relation schemas?

• Physical Design – Deciding on the physical layout of the database

Design Approaches

• Need to come up with a methodology to ensure that each of the relations in the database is “good”

• Two ways of doing so:• Entity Relationship Model (Chapter 7)

• Models an enterprise as a collection of entities and relationships

• Represented diagrammatically by an entity-relationship diagram

• Normalization Theory (Chapter 8)• Formalize what designs are bad, and test for them

A Part of an ER Diagram

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A More Elaborate ER Model

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Database Design (Cont.)

• Is there any problem with this relation?

Database Engine

• Storage manager

• Query processing

• Transaction manager

Storage Management

• Storage manager is a program module that provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system.

• The storage manager deals with:• File organization

• Indexing and hashing

• and anything that is low-level concerning the data storage.

File Organization

• The database is stored as a collection of files. Each file is a sequence of records. A record is a sequence of fields.

• One approach:•assume record size is fixed

•each file has records of one particular type only

•different files are used for different relations

Query Processing

How to effectively execute the query?

Select Operation – selection of rows (tuples)

Relation r

(A=B) ^ (D > 5) (r)

Transaction Management

• A transaction is a unit of program execution that accesses and possibly updates various data items.

• E.g., transaction to transfer $50 from account A to account B:

1. read(A)

2. A := A – 50

3. write(A)

4. read(B)

5. B := B + 50

6. write(B)

• Two main issues to deal with:• Failures of various kinds, such as hardware failures and

system crashes• Concurrent execution of multiple transactions

Summary and Course Plan*

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Topics Text Book Reference

Introduction to RDBMS Chapters 1, 2

SQL Chapters 3, 4

Relational Model Relational Algebra

Chapters 6

Relational Database Design Functional Dependencies, Normal Forms, Keys, Decomposition

Chapters 7, 8

Data Storage and Querying Storage, Indexing Structures

Chapters 10, 11

Transaction ManagementACID Properties, Transactions, Concurrency control, Serialization

Chapter 14

* Tentative