Database System Concepts, 5th Ed.
Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
Chapter 1: IntroductionChapter 1: Introduction
Silberschatz, Korth and Sudarshan1.2Database System Concepts - 5th Edition, Sep 6, 2006
Chapter 1: IntroductionChapter 1: Introduction
Purpose of Database Systems
View of Data
Database Languages
Relational Databases
Database Design
Object-based and semistructured databases
Data Storage and Querying
Transaction Management
Database Architecture
Database Users and Administrators
Overall Structure
History of Database Systems
Silberschatz, Korth and Sudarshan1.3Database System Concepts - 5th Edition, Sep 6, 2006
Database Management System (DBMS)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: all 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 touch all aspects of our lives
Silberschatz, Korth and Sudarshan1.4Database System Concepts - 5th Edition, Sep 6, 2006
Purpose of Database SystemsPurpose of Database Systems
In the early days, database applications were built directly on top of
file systems
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
Silberschatz, Korth and Sudarshan1.5Database System Concepts - 5th Edition, Sep 6, 2006
Purpose of Database Systems (Cont.)Purpose of Database Systems (Cont.)
Drawbacks of using file 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 complete or not happen at all
Concurrent access by multiple users
Concurrent accessed needed for performance
Uncontrolled concurrent accesses can lead to inconsistencies
­ Example: Two people reading a balance and updating it 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 Sudarshan1.6Database System Concepts - 5th Edition, Sep 6, 2006
Levels of AbstractionLevels of Abstraction
Physical level: describes how a record (e.g., customer) is stored.
Logical level: describes data stored in database, and the relationships
among the data.
type customer = record
customer_id : string;
customer_name : string;
customer_street : string;
customer_city : integer;
end
View level: A way to hide: (a) details of data types and (b) information
(such as an employee's salary) for security purposes.
Silberschatz, Korth and Sudarshan1.7Database System Concepts - 5th Edition, Sep 6, 2006
View of DataView of Data
An architecture for a database system
Silberschatz, Korth and Sudarshan1.8Database System Concepts - 5th Edition, Sep 6, 2006
Instances and SchemasInstances and Schemas
Similar to types and variables in programming languages
Schema ­ the logical structure of the database
Example: The database consists of information about a set of customers and
accounts and the relationship between them)
Analogous to type information of a variable in a program
Physical schema: database design at the physical level
Logical schema: database design at the logical level
Instance ­ the actual content of the database at a particular point in time
Analogous to the value of a variable
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 Sudarshan1.9Database System Concepts - 5th Edition, Sep 6, 2006
Data ModelsData 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
Silberschatz, Korth and Sudarshan1.10Database System Concepts - 5th Edition, Sep 6, 2006
Data Manipulation Language (DML)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
Silberschatz, Korth and Sudarshan1.11Database System Concepts - 5th Edition, Sep 6, 2006
Data Definition Language (DDL)Data Definition Language (DDL)
Specification notation for defining the database schema
Example: create table account (
account-number char(10),
balance integer)
DDL compiler generates a set of tables stored in a data dictionary
Data dictionary contains metadata (i.e., data about data)
Database schema
Integrity constraints
Domain constraints
Referential integrity (references constraint in SQL)
Assertions
Authorization
Data storage and definition language
Specifies the storage structure and access methods used
Silberschatz, Korth and Sudarshan1.12Database System Concepts - 5th Edition, Sep 6, 2006
Relational DatabasesRelational Databases
A relational database is based on the relational data model
Data and relationships among the data is represented by a
collection of tables
Includes both a DML and a DDL
Most commercial relational database systems employ the SQL
query langue.
Silberschatz, Korth and Sudarshan1.13Database System Concepts - 5th Edition, Sep 6, 2006
Relational ModelRelational Model
Example of tabular data in the relational model
Attributes
Silberschatz, Korth and Sudarshan1.14Database System Concepts - 5th Edition, Sep 6, 2006
A Sample Relational DatabaseA Sample Relational Database
Silberschatz, Korth and Sudarshan1.15Database System Concepts - 5th Edition, Sep 6, 2006
SQLSQL
SQL: widely used non-procedural language
Example: Find the name of the customer with customer-id 192-83-7465
select customer.customer_name
from customer
where customer.customer_id = `192-83-7465'
Example: Find the balances of all accounts held by the customer with
customer-id 192-83-7465
select account.balance
from depositor, account
where depositor.customer_id = `192-83-7465' and
depositor.account_number = account.account_number
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
Silberschatz, Korth and Sudarshan1.16Database System Concepts - 5th Edition, Sep 6, 2006
Database DesignDatabase 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
Silberschatz, Korth and Sudarshan1.17Database System Concepts - 5th Edition, Sep 6, 2006
The EntityThe Entity--Relationship ModelRelationship 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:
Silberschatz, Korth and Sudarshan1.18Database System Concepts - 5th Edition, Sep 6, 2006
ObjectObject--Relational Data ModelsRelational Data Models
Extend the relational data model by including object orientation and
constructs to deal with added data types.
Allow attributes of tuples to have complex types, including non-atomic
values such as nested relations.
Preserve relational foundations, in particular the declarative access to
data, while extending modeling power.
Provide upward compatibility with existing relational languages.
Silberschatz, Korth and Sudarshan1.19Database System Concepts - 5th Edition, Sep 6, 2006
XML: Extensible Markup LanguageXML: Extensible Markup Language
Defined by the WWW Consortium (W3C)
Originally intended as a document markup language not a
database language
The ability to specify new tags, and to create nested tag structures
made XML a great way to exchange data, not just documents
XML has become the basis for all new generation data interchange
formats.
A wide variety of tools is available for parsing, browsing and
querying XML documents/data
Silberschatz, Korth and Sudarshan1.20Database System Concepts - 5th Edition, Sep 6, 2006
Storage ManagementStorage 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
Silberschatz, Korth and Sudarshan1.21Database System Concepts - 5th Edition, Sep 6, 2006
Query ProcessingQuery Processing
1. Parsing and translation
2. Optimization
3. Evaluation
Silberschatz, Korth and Sudarshan1.22Database System Concepts - 5th Edition, Sep 6, 2006
Query Processing (Cont.)Query Processing (Cont.)
Alternative ways of evaluating a given query
Equivalent expressions
Different algorithms for each operation
Cost difference between a good and a bad way of evaluating a query can
be enormous
Need to estimate the cost of operations
Depends critically on statistical information about relations which the
database must maintain
Need to estimate statistics for intermediate results to compute cost of
complex expressions
Silberschatz, Korth and Sudarshan1.23Database System Concepts - 5th Edition, Sep 6, 2006
Transaction ManagementTransaction 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 Sudarshan1.24Database System Concepts - 5th Edition, Sep 6, 2006
Database ArchitectureDatabase 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
Silberschatz, Korth and Sudarshan1.25Database System Concepts - 5th Edition, Sep 6, 2006
Database UsersDatabase Users
Users are differentiated by the way they expect to interact with
the system
Application programmers ­ interact with system through DML calls
Sophisticated users ­ form requests in a database query language
Specialized users ­ write specialized database applications that do
not fit into the traditional data processing framework
Nave users ­ invoke one of the permanent application programs that
have been written previously
Examples, people accessing database over the web, bank tellers,
clerical staff
Silberschatz, Korth and Sudarshan1.26Database System Concepts - 5th Edition, Sep 6, 2006
Database AdministratorDatabase Administrator
Coordinates all the activities of the database system; the
database administrator has a good understanding of the
enterprise's information resources and needs.
Database administrator's duties include:
Schema definition
Storage structure and access method definition
Schema and physical organization modification
Granting user authority to access the database
Specifying integrity constraints
Acting as liaison with users
Monitoring performance and responding to changes in
requirements
Silberschatz, Korth and Sudarshan1.27Database System Concepts - 5th Edition, Sep 6, 2006
Overall System StructureOverall System Structure
Silberschatz, Korth and Sudarshan1.28Database System Concepts - 5th Edition, Sep 6, 2006
History of Database SystemsHistory of Database Systems
1950s and early 1960s:
Data processing using magnetic tapes for storage
Tapes provide only sequential access
Punched cards for input
Late 1960s and 1970s:
Hard disks allow 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
Silberschatz, Korth and Sudarshan1.29Database System Concepts - 5th Edition, Sep 6, 2006
History (cont.)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
2000s:
XML and XQuery standards
Automated database administration
Database System Concepts, 5th Ed.
Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
End of Chapter 1End of Chapter 1
Silberschatz, Korth and Sudarshan1.31Database System Concepts - 5th Edition, Sep 6, 2006
Figure 1.4Figure 1.4
Silberschatz, Korth and Sudarshan1.32Database System Concepts - 5th Edition, Sep 6, 2006
Figure 1.7Figure 1.7