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CSE 480: Database Systems

Lecture 1: Introduction

Reference:

Read Chapters 1 & 2 of the textbook

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Database Systems are Pervasive

Retail

Banking

Law enforcement

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Database-Driven Web Sites

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What is a Database?

Collection of related data central to a given enterprise (mini-world or universe of discourse)

– Examples: Banking – savings/checking accounts, mortgage, etc Vehicle registration – car registration, year, make, etc Student registration – name, PID, GPA, last semester enrolled, etc Electronic Medical Records – name, SSN, date of birth, address,

symptoms, diseases, medication, test results, etc

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Example of a Database

Mini-world: UNIVERSITY environment– What are the mini-world concepts that need to be captured by

the database?

Entities:– STUDENTs

– COURSEs

– SECTIONs

– DEPARTMENTs

– INSTRUCTORs

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Example of a Database

Relationships between entities of the mini-world:– SECTIONs are for specific COURSEs

– STUDENTs take SECTIONs

– COURSEs have prerequisite COURSEs

– INSTRUCTORs teach SECTIONs

– COURSEs are offered by DEPARTMENTs

– STUDENTs major in DEPARTMENTs

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Example of a Database

Constraints on the entities and relationships– Each course must have a unique course number

– GPA must be a real number between 0 and 4.0

– Each section has only one instructor but an instructor can teach more than one section

Database design (Lectures 2-4)– Specifying the entities, relationships, and

constraints of a mini-world using the Entity-Relationship and Enhanced Entity Relationship models.

Database Architect or Designer

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Database Management System (DBMS)

A collection of programs that enables users to create and maintain a database

Examples of DBMS– MS Access, MS SQL Server, IBM DB2, Oracle, Sybase,

Postgres, mySQL, and many more

Why do we need a DBMS?

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File Server Architecture (no DBMS)

Source: Modern Database Management. 6th Edition, Jeffrey A. Hoffer, Mary B. Prescott, Fred R. McFadden

Thick clientThick client

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Client-Server DBMS Architecture

Source: Modern Database Management. 6th Edition, Jeffrey A. Hoffer, Mary B. Prescott, Fred R. McFadden

DBMS running on database server; performs all data storage and access operations

Thin clientThin client

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Three-tier Architecture

Business rules stored on Business rules stored on application serverapplication server

Source: Modern Database Management. 6th Edition, Jeffrey A. Hoffer, Mary B. Prescott, Fred R. McFadden

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Typical DBMS Functionalities

Define a database – Specify the structure of the data records

Construct a database– Store the data on some storage medium controlled by the DBMS

Manipulate the database – Query the database to retrieve specific data, update the database to

reflect changes, and generate reports

Support concurrent processing and sharing by users and applications– yet, keeping all the data valid and consistent

Support protection/security measures to prevent unauthorized access

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Characteristics of DBMS

Self-Describing Provides insulation between programs and data Allows multiple views Allows multi-user transaction processing

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Characteristics of DBMS

Self-describing nature of a database management system– DBMS contains not only the data but also complete description

of its structure and constraints Structure: Student ID is 10 characters long, GPA is a real number Constraints: GPA must be between 0 and 4.0 (non-negative)

– A DBMS catalog stores the description of the database The description is called meta-data

– This allows the DBMS software to work with any types of data (banking, university, company, etc)

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Example of DBMS Catalog

Information in DBMS catalog are needed for query processing and optimization (to be discussed more in lectures 22-24)

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Characteristics of DBMS

Insulation between programs and data – Program-data independence

Allows changing data storage structures and operations without changing the DBMS access programs

– Program-operation independence In OO and OR database systems, users can define operations

(methods) on data using an interface; implementation of the operation (method) can be separately specified

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Characteristics of DBMS

Support multiple views of the data– A database typically has many users, each of whom require

different perspective (view) of the database

– A common principle used by many organizations is that data must be accessible on a need-to-know basis

– Example: Student database may contain information about student’s name,

SSN, courses taken and grades, salary, etc Users of the database include registrar office and payroll department

– Registrar doesn’t need to know what is student’s salary

– Payroll doesn’t need to know what is student’s GPA

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Characteristics of DBMS

Multi-user transaction processing – Database stores information about current state of an enterprise

Example: Bank database stores balance for each customer account

– When an event in the real world changes, a transaction is executed to cause corresponding change in the database state A transaction is an executing program or process that includes one

or more database accesses, such as reading or updating database records

Each transaction is designed to maintain correctness of the relationship between database state and real-world enterprise it is modeling

– Example: When a customer deposits $50 in a bank, a deposit transaction is executed to increase the account balance by $50

– Concurrency control of DBMS ensures correctness of the database when multiple concurrent transactions are executed

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Database System Concepts

Data Models Database Schema vs Database Instances DBMS Languages

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Abstraction

Data is actually stored as bits, but it is difficult to work with data at this level

DBMS provides a level of abstraction by hiding the details of data organization and storage

– A data model is used to hide storage details and present the users with a conceptual view of the database

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Data Model

111000010010111011010111011011

User/Program

(John, 21)(Mary, 19)

(CSE480)(CSE331)

(CSE, Engr)(ECE, Engr)

Physical data storage

Data model

Student Course Department

DBMS

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Examples of Data Models

Network Model Hierarchical Model Relational Model (most widely used) Object-Oriented Data Models Object-Relational Models

More recently, NoSQL– Google BigTable

– Amazon Dynamo

– Facebook Cassandra

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Relational Data Model

Proposed by Edgar Codd– E. F. Codd: A Relational Model of Data for Large

Shared Data Banks. Commun. ACM 13(6): 377-387 (1970)

Model the data as relations (tables)– Advantages:

Simple Mathematically based Has a set of powerful, high-level operators to analyze relational

expressions ( queries)

– Queries are transformed to equivalent expressions automatically (query processing and optimization) Transformed expressions can be executed more efficiently

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Database Schemas versus Instances

In any data model, it is important to distinguish between description of the database from the database itself

Database Schema:– The description of a database

Includes descriptions of data elements, data types, and constraints

– Schema Diagram: An illustrative display of a database schema

Database Instance (State/Snapshot):– The actual data stored in the database at a particular moment

in time

– Valid State: A state that satisfies the structure and constraints of the database

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Example of a Database Schema

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Example of a Database State

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Database Schema vs. Database State

Distinction– The database schema changes very infrequently.

– The database state changes every time the database is updated.

Schema is also called intension State is also called extension

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Three-Schema Architecture

Externalschemas

Internal Schema

Physical storage for data about students, courses, employment, etc

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Internal Schema/Level

Describes the details of how data is physically stored – Specify how data is stored in files, tracks, cylinders.

– Specify the indices that support fast access to the rows of a table

– Specify the machine that has the data (Data may be distributed)

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Conceptual Schema/Level

Hides the details of physical data representation– In the relational model, the conceptual schema presents data as

a set of tables (relations)

DBMS maps from conceptual to internal schema automatically

Physical data independence – Internal schema can be changed without changing the

conceptual schema

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External Schema/Level

External schema customizes the conceptual schema to the needs of various users

In the relational model, the external schema also presents data as a set of relations

Externalschemas

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External Schema

Application is written in terms of an external schema.– Different external schemas can be provided to different

categories of users

DBMS maps external to conceptual schema automatically at run time

Logical data independence – Conceptual schema can be changed without changing external

schema and application programs

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DBMS Languages

Data Definition Language (DDL): – Used to specify the conceptual schema of a database

In many DBMSs, DDL is also used to define internal and external schemas (views).

In some DBMSs, separate storage definition language (SDL) and view definition language (VDL) are used to define internal and external schemas

CREATE TABLE DEPARTMENT (DNAME VARCHAR(10) NOT NULL,DNUMBER INTEGER NOT NULL,MGRSSN CHAR(9),MGRSTARTDATE CHAR(9)

);

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DBMS Languages

Data Manipulation Language (DML)– Used to specify database retrievals and updates

– Both DML and DDL can be embedded in a general-purpose programming language, such as C, C++, Java or PHP

INSERT INTO DEPARTMENT VALUES (‘Payroll’, 154, ‘123-11-2344’, ‘2005-06-22’);

SELECT MgrSSNFROM DEPARTMENTWHERE DName = ‘Payroll’;

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Example of SQL Embedded in Java

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Database System Environment

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MySQL Account

Every registered student will have access to a MySQL account on mysql-user.cse.msu.edu

To log in, go to:– http://www.cse.msu.edu/facility/phpMyAdmin/index.php

– Username is your CSE usernamePassword is your PIDServer Choice: mysql-user

Send an email to manager@cse.msu.edu if you have problems logging in