Database System Concepts, 7th Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
Chapter 1: Introduction
©Silberschatz, Korth and Sudarshan1.2Database System Concepts - 7th Edition
Before we Start
▪ Slides in English – talk in Czech
▪ Exercises in groups do not cover all the topics from the lessons
▪ Examination by tests:
• Exactly one correct answer for exercises tests
• One or more correct answers for the course examination
▪ A successful exercises test is a condition for the course examination
registration
©Silberschatz, Korth and Sudarshan1.3Database System Concepts - 7th Edition
Outline
▪ Database-System Applications
▪ Purpose of Database Systems
▪ View of Data
▪ Database Languages
▪ Database Design
▪ Database Engine
▪ Database Architecture
▪ Database Users and Administrators
▪ History of Database Systems
©Silberschatz, Korth and Sudarshan1.4Database System Concepts - 7th Edition
Database Systems
▪ 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 systems are used to manage collections of data that are:
• Highly valuable
• Relatively large size
• Accessed by multiple users and applications, often at the same
time.
▪ A modern database system is a complex software system whose task
is to manage a large, complex collection of data.
▪ Databases touch all aspects of our lives
©Silberschatz, Korth and Sudarshan1.5Database System Concepts - 7th Edition
Database Applications Examples
▪ Enterprise Information
• Sales: customers, products, purchases
• Accounting: payments, receipts, assets
• Human Resources: Information about employees, salaries, payroll
taxes.
▪ Manufacturing: management of production, inventory, orders, supply
chain.
▪ Banking and finance
• customer information, accounts, loans, and banking transactions.
• Credit card transactions
• Finance: sales and purchases of financial instruments (e.g., stocks
and bonds; storing real-time market data
▪ Universities: registration, grades
©Silberschatz, Korth and Sudarshan1.6Database System Concepts - 7th Edition
Database Applications Examples (Cont.)
▪ Airlines: reservations, schedules
▪ Telecommunication: records of calls, texts, and data usage, generating
monthly bills, maintaining balances on prepaid calling cards
▪ Web-based services
• Online retailers: order tracking, customized recommendations
• Online advertisements
▪ Document databases
▪ Navigation systems: For maintaining the locations of varies places of
interest along with the exact routes of roads, train systems, buses, etc.
©Silberschatz, Korth and Sudarshan1.7Database System Concepts - 7th Edition
Purpose of Database Systems
▪ Data redundancy and inconsistency: data is stored in multiple file
formats resulting in 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
In the early days, database applications were built directly on top of file
systems, which leads to:
©Silberschatz, Korth and Sudarshan1.8Database System Concepts - 7th Edition
Purpose of Database Systems (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
be completed or not happen at all
▪ Concurrent access by multiple users
• Concurrent access needed for performance
• Uncontrolled concurrent accesses can lead to inconsistencies
▪ Ex: 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
©Silberschatz, Korth and Sudarshan1.9Database System Concepts - 7th Edition
University Database Example
▪ In this text we will be using a university database to illustrate all the
concepts
▪ Data consists of information about:
• Students
• Instructors
• Classes
▪ 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
©Silberschatz, Korth and Sudarshan1.10Database System Concepts - 7th Edition
View of Data
▪ A database system is a collection of interrelated data and a set of
programs that allow users to access and modify these data.
▪ A major purpose of a database system is to provide users with an abstract
view of the data.
• Data models
▪ A collection of conceptual tools for describing data, data
relationships, data semantics, and consistency constraints.
• Data abstraction
▪ Hide the complexity of data structures to represent data in the
database from users through several levels of data abstraction.
©Silberschatz, Korth and Sudarshan1.11Database System Concepts - 7th Edition
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)
▪ Semi-structured data model (XML)
▪ Other older models:
• Network model
• Hierarchical model
©Silberschatz, Korth and Sudarshan1.12Database System Concepts - 7th Edition
Relational Model
▪ All the data is stored in various tables.
▪ Example of tabular data in the relational model
Columns
Rows
Ted Codd
Turing Award 1981
©Silberschatz, Korth and Sudarshan1.13Database System Concepts - 7th Edition
A Sample Relational Database
©Silberschatz, Korth and Sudarshan1.14Database System Concepts - 7th Edition
Levels of Abstraction
▪ Physical level: describes how a record (e.g., instructor) is stored.
▪ Logical level: describes data stored in database, and the relationships
among the data.
type instructor = record
ID : string;
name : string;
dept_name : string;
salary : integer;
end;
▪ View level: application programs hide details of data types. Views can
also hide information (such as an employee’s salary) for security
purposes.
©Silberschatz, Korth and Sudarshan1.15Database System Concepts - 7th Edition
View of Data
An architecture for a database system
©Silberschatz, Korth and Sudarshan1.16Database System Concepts - 7th Edition
Instances and Schemas
▪ Analogously to types and variables in programming languages
▪ Logical Schema – the overall logical structure of the database
• Example: The database consists of information about a set of
customers and accounts in a bank and the relationship between them
▪ Analogous to type information of a variable in a program
▪ Physical Schema – the overall physical structure of the database
▪ Instance – the actual content of the database at a particular point in time
• Analogous to the value of a variable
©Silberschatz, Korth and Sudarshan1.17Database System Concepts - 7th Edition
Physical Data Independence
▪ Physical Data Independence – the ability to modify the physical
schema without changing the logical schema
• Applications depend on the logical schema
• In general, the interfaces between the various levels and
components should be well defined so that changes in some parts
do not seriously influence others.
©Silberschatz, Korth and Sudarshan1.18Database System Concepts - 7th Edition
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)
• Authorization
▪ Who can access what
©Silberschatz, Korth and Sudarshan1.19Database System Concepts - 7th Edition
Data Manipulation Language (DML)
▪ Language for accessing and updating the data organized by the
appropriate data model
• DML also known as query language
▪ There are basically two types of data-manipulation language
• Procedural DML -- require a user to specify what data are needed
and how to get those data.
• Declarative DML -- require a user to specify what data are needed
without specifying how to get those data.
▪ Declarative DMLs are usually easier to learn and use than are procedural
DMLs.
▪ Declarative DMLs are also referred to as non-procedural DMLs
▪ The portion of a DML that involves retrieval of information is called a
query language.
©Silberschatz, Korth and Sudarshan1.20Database System Concepts - 7th Edition
SQL Query Language
▪ SQL query language is nonprocedural. A query takes as input several
tables (possibly only one) and always returns a single table.
▪ Example to find all instructors in Comp. Sci. dept
select name
from instructor
where dept_name = 'Comp. Sci.'
▪ To be able to compute complex functions SQL is usually embedded in
some higher-level language
▪ Application programs generally access databases through one of
• Language extensions to allow embedded SQL
• Application program interface (e.g., ODBC/JDBC – Open/Java
Database Connectivity) which allow SQL queries to be sent to a
database
©Silberschatz, Korth and Sudarshan1.21Database System Concepts - 7th Edition
Database Access from Application Program
▪ Non-procedural query languages such as SQL are not as powerful as a
universal Turing machine.
▪ SQL does not support actions such as input from users, output to
displays, or communication over the network.
▪ Such computations and actions must be written in a host language, such
as C/C++, Java or Python, with embedded SQL queries that access the
data in the database.
▪ Application programs -- are programs that are used to interact with the
database in this fashion.
©Silberschatz, Korth and Sudarshan1.22Database System Concepts - 7th Edition
Database Design
▪ Logical Design – Deciding about the database schema. Database
design requires that we find a “good” collection of relation schemas.
• Application 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
The process of designing the general structure of the database:
©Silberschatz, Korth and Sudarshan1.23Database System Concepts - 7th Edition
Database Engine
▪ A database system is partitioned into modules that deal with each of the
responsibilities of the overall system.
▪ The functional components of a database system can be divided into
• The storage manager,
• The query processor component,
• The transaction management component.
©Silberschatz, Korth and Sudarshan1.24Database System Concepts - 7th Edition
Storage Manager
▪ 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 OS file manager
• Efficient storing, retrieving and updating of data
▪ The storage manager components include:
• Authorization and integrity manager
• Transaction manager
• File manager
• Buffer manager
©Silberschatz, Korth and Sudarshan1.25Database System Concepts - 7th Edition
Storage Manager (Cont.)
▪ The storage manager implements several data structures as part of the
physical system implementation:
• Data files -- store the database itself
• Data dictionary -- stores metadata about the structure of the
database, in particular the schema of the database.
• Indices -- can provide fast access to data items. A database index
provides pointers to those data items that hold a particular value.
©Silberschatz, Korth and Sudarshan1.26Database System Concepts - 7th Edition
Query Processor
▪ The query processor components include:
• DDL interpreter -- interprets DDL statements and records the
definitions in the data dictionary.
• DML compiler -- translates DML statements in a query language into
an evaluation plan consisting of low-level instructions that the query
evaluation engine understands.
▪ The DML compiler performs query optimization; that is, it picks
the lowest cost evaluation plan from among the various equivalent
alternatives.
• Query evaluation engine -- executes low-level instructions generated
by the DML compiler.
©Silberschatz, Korth and Sudarshan1.27Database System Concepts - 7th Edition
Query Processing
1. Parsing and translation
2. Optimization
3. Evaluation
©Silberschatz, Korth and Sudarshan1.28Database System Concepts - 7th Edition
Transaction Management
▪ 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.
©Silberschatz, Korth and Sudarshan1.29Database System Concepts - 7th Edition
Database Architecture
▪ Centralized databases
• One to a few cores, shared memory
▪ Client-server,
• One server machine executes work on behalf of multiple client
machines.
▪ Parallel databases
• Many core shared memory
• Shared disk
• Shared nothing
▪ Distributed databases
• Geographical distribution
• Schema/data heterogeneity
©Silberschatz, Korth and Sudarshan1.30Database System Concepts - 7th Edition
Database Architecture
(Centralized/Shared-Memory)
©Silberschatz, Korth and Sudarshan1.31Database System Concepts - 7th Edition
Database Applications
▪ Two-tier architecture -- the application resides at the client machine,
where it invokes database system functionality at the server machine
▪ Three-tier architecture -- the client machine acts as a front end and
does not contain any direct database calls.
• The client end communicates with an application server, usually
through a forms interface.
• The application server in turn communicates with a database
system to access data.
Database applications are usually partitioned into two or three parts
©Silberschatz, Korth and Sudarshan1.32Database System Concepts - 7th Edition
Two-tier and three-tier architectures
©Silberschatz, Korth and Sudarshan1.33Database System Concepts - 7th Edition
Database Users
©Silberschatz, Korth and Sudarshan1.34Database System Concepts - 7th Edition
Database Administrator
▪ Schema definition
▪ Storage structure and access-method definition
▪ Schema and physical-organization modification
▪ Granting of authorization for data access
▪ Routine maintenance
▪ Periodically backing up the database
▪ Ensuring that enough free disk space is available for normal
operations, and upgrading disk space as required
▪ Monitoring jobs running on the database
A person who has central control over the system is called a database
administrator (DBA). Functions of a DBA include:
©Silberschatz, Korth and Sudarshan1.35Database System Concepts - 7th Edition
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 (Michael Stonebraker) begins Ingres prototype
▪ Oracle releases first commercial relational database
• High-performance (for the era) transaction processing
©Silberschatz, Korth and Sudarshan1.36Database System Concepts - 7th Edition
History of Database Systems (Cont.)
▪ 1980s:
• Research relational prototypes evolve into commercial systems
▪ SQL becomes industrial standard
• Parallel and distributed database systems
▪ Wisconsin, IBM, Teradata
• Object-oriented database systems
▪ 1990s:
• Large decision support and data-mining applications
• Large multi-terabyte data warehouses
• Emergence of Web commerce
©Silberschatz, Korth and Sudarshan1.37Database System Concepts - 7th Edition
History of Database Systems (Cont.)
▪ 2000s
• Big data storage systems
▪ Google BigTable, Yahoo PNuts, Amazon,
▪ “NoSQL” systems.
• Big data analysis: beyond SQL
▪ Map reduce and friends
▪ 2010s
• SQL reloaded
▪ SQL front end to Map Reduce systems
▪ Massively parallel database systems
▪ Multi-core main-memory databases
©Silberschatz, Korth and Sudarshan1.38Database System Concepts - 7th Edition
End of Chapter 1