Chapter 1: Introduction

Database System Concepts, 6th Ed.
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Database Management System (DBMS)
 DBMS contains information about a particular enterprise


Collection of interrelated data



Set of programs to access the data



An environment that is both convenient and efficient to use

 Database Applications:


Banking: transactions



Airlines: reservations, schedules



Universities: registration, grades



Sales: customers, products, purchases

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Online retailers: order tracking, customized recommendations

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Manufacturing: production, inventory, orders, supply chain



Human resources: employee records, salaries, tax deductions

 Databases can be very large.
 Databases touch all aspects of our lives
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University Database Example
 Application program examples
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Add new students, instructors, and courses

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Register students for courses, and generate class rosters



Assign grades to students, compute grade point averages (GPA) and generate transcripts

 In the early days, database applications were built directly on top of

file systems

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Drawbacks of using file systems to store data


Data redundancy and inconsistency


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Multiple file formats, duplication of information in different files

Difficulty in accessing data


Need to write a new program to carry out each new task

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Data isolation — multiple files and formats

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Integrity problems


Integrity constraints (e.g., account balance > 0) become
“buried” in program code rather than being stated explicitly



Hard to add new constraints or change existing ones

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Drawbacks of using file systems to store data (Cont.)



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Atomicity of updates
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Failures may leave database in an inconsistent state with partial updates carried out



Example: Transfer of funds from one account to another should either complete or not happen at all

Concurrent access by multiple users


Concurrent access needed for performance



Uncontrolled concurrent accesses can lead to inconsistencies
– Example: Two people reading a balance (say 100) and updating it by withdrawing money (say 50 each) at the same time



Security problems


Hard to provide user access to some, but not all, data

Database systems offer solutions to all the above problems

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Data Models
 A collection of tools for describing

Data
 Data relationships
 Data semantics
 Data constraints


 Relational model
 Entity­Relationship data model (mainly for database design)
 Object­based data models (Object­oriented and Object­relational)
 Semistructured data model (XML)
 Other older models:



Network model
Hierarchical model

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Relational Model
 Relational model (Chapter 2)
 Example of tabular data in the relational model

Columns

Rows

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A Sample Relational Database

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Data Definition Language (DDL)


Specification notation for defining the database schema
Example:
create table instructor ( ID char(5), name varchar(20), dept_name varchar(20), salary numeric(8,2))



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

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



Integrity constraints


Primary key (ID uniquely