Database System Concepts, 6th Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
Chapter 1: Introduction
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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
Online retailers: order tracking, customized recommendations
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
Add new students, instructors, and courses
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
 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
Data isolation — multiple files and formats
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.)
Atomicity of updates
 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
Entity-Relationship data model (mainly for database design)
Object-based data models (Object-oriented and Object-relational)
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 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
Procedural – user specifies what data is required and how to get
those data
Declarative (nonprocedural) – user specifies what data is
required without specifying how to get those data
SQL is the most widely used query language
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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
Data dictionary contains metadata (i.e., data about data)
Database schema
Integrity constraints
 Primary key (ID uniquely identifies instructors)
 Referential integrity (references constraint in SQL)
– e.g. dept_name value in any instructor tuple must appear in
department relation
Authorization
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SQL
SQL: widely used non-procedural language
Example: Find the name of the instructor with ID 22222
select name
from instructor
where instructor.ID = ‘22222’
Example: Find the ID and building of instructors in the Physics dept.
select instructor.ID, department.building
from instructor, department
where instructor.dept_name = department.dept_name and
department.dept_name = ‘Physics’
Application programs generally access databases through one of
Language extensions to allow embedded SQL
Application program interface (e.g., ODBC/JDBC) which allows SQL
queries to be sent to a database
Chapters 3, 4 and 5
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Database Design?
Is there any problem with this design?
Table instructor
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Design Approaches
Normalization Theory (Chapter 8)
Formalize what designs are bad, and test for them
Entity Relationship Model (Chapter 7)
Models an enterprise as a collection of entities and relationships
 Entity: a “thing” or “object” in the enterprise that is
distinguishable from other objects
– Described by a set of attributes
 Relationship: an association among several entities
Represented diagrammatically by an entity-relationship diagram:
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The Entity-Relationship Model
Models an enterprise as a collection of entities and relationships
Entity: a “thing” or “object” in the enterprise that is distinguishable
from other objects
 Described by a set of attributes
Relationship: an association among several entities
Represented diagrammatically by an entity-relationship diagram:
What happened to dept_name of instructor?
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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 is responsible to the following tasks:
Interaction with the file manager
Efficient storing, retrieving and updating of data
Issues:
Storage access
File organization
Indexing and hashing
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Query Processing
1. Parsing and translation
2. Optimization
3. Evaluation
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Transaction Management
What if the system fails?
What if more than one user is concurrently updating the same data?
A transaction is a collection of operations that performs a single
logical function in a database application
Transaction-management component ensures that the database
remains in a consistent (correct) state despite system failures (e.g.,
power failures and operating system crashes) and transaction failures.
Concurrency-control manager controls the interaction among the
concurrent transactions, to ensure the consistency of the database.
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Database System Internals
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Database Architecture
The architecture of a database systems is greatly influenced by
the underlying computer system on which the database is running:
Centralized
Client-server
Parallel (multi-processor)
Distributed
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History of Database Systems
1950s and early 1960s:
Data processing using magnetic tapes for storage
 Tapes provided only sequential access
Punched cards for input
Late 1960s and 1970s:
Hard disks allowed direct access to data
Network and hierarchical data models in widespread use
Ted Codd defines the relational data model
 Would win the ACM Turing Award for this work
 IBM Research begins System R prototype
 UC Berkeley begins Ingres prototype
High-performance (for the era) transaction processing
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History (cont.)
1980s:
Research relational prototypes evolve into commercial systems
 SQL becomes industrial standard
Parallel and distributed database systems
Object-oriented database systems
1990s:
Large decision support and data-mining applications
Large multi-terabyte data warehouses
Emergence of Web commerce
Early 2000s:
XML and XQuery standards
Automated database administration
Later 2000s:
Giant data storage systems
 Google BigTable, Yahoo PNuts, Amazon, ..
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End of Chapter 1