6846222.pdf

Database System Concepts, 5th Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
Chapter 1: Introduction

1.2
Database System Concepts - 5th
Edition, May 23, 2005
Chapter 1: Introduction
• Purpose of Database Systems
• Database Languages
• Relational Databases
• Database Design
• Data Models
• Database Internals
• Database Users and Administrators
• Overall Structure
• History of Database Systems

1.3
Database Management System (DBMS)
• DBMS contains information about a particular enterprise
o Collection of interrelated data
o Set of programs to access the data
o An environment that is both convenient and efficient to use
• Database Applications:
o Banking: all transactions
o Airlines: reservations, schedules
o Universities: registration, grades
o Sales: customers, products, purchases
o Online retailers: order tracking, customized recommendations
o Manufacturing: production, inventory, orders, supply chain
o Human resources: employee records, salaries, tax deductions
• Databases touch all aspects of our lives

1.4
Purpose 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:
o Data redundancy and inconsistency
 Multiple file formats, duplication of information in different files
o Difficulty in accessing data
 Need to write a new program to carry out each new task
o Data isolation — multiple files and formats
o 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

1.5
Purpose of Database Systems (Cont.)
• Drawbacks of using file systems (cont.)
o 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
o 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
o Security problems
 Hard to provide user access to some, but not all, data
• Database systems offer solutions to all the above problems

1.6
Levels 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 : string;
end;
• View level: application programs hide details of data types. Views can
also hide information (such as an employee’s salary) for security
purposes.

1.7
View of Data
An architecture for a database system

1.8
Instances and Schemas
• Similar to types and variables in programming languages
• Schema – the logical structure of the database
o Example: The database consists of information about a set of customers and
accounts and the relationship between them)
o Analogous to type information of a variable in a program
o Physical schema: database design at the physical level
o Logical schema: database design at the logical level
• Instance – the actual content of the database at a particular point in time
o Analogous to the value of a variable
• Physical Data Independence – the ability to modify the physical schema without
changing the logical schema
o Applications depend on the logical schema
o 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.

1.9
Data Models
• A collection of tools for describing
o Data
o Data relationships
o Data semantics
o 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:
o Network model
o Hierarchical model

1.10
Data Manipulation Language (DML)
• Language for accessing and manipulating the data organized by the
appropriate data model
o DML also known as query language
• Two classes of languages
o Procedural – user specifies what data is required and how to get
those data
o Declarative (nonprocedural) – user specifies what data is
required without specifying how to get those data
• SQL is the most widely used query language

1.11
Data Definition Language (DDL)
• Specification notation for defining the database schema
Example: create table account (
account_number char(10),
branch_name 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)
o Database schema
o Data storage and definition language
 Specifies the storage structure and access methods used
o Integrity constraints
 Domain constraints
 Referential integrity (e.g. branch_name must correspond to a
valid branch in the branch table)
o Authorization

1.12
Relational Model
• Example of tabular data in the relational model
Attributes

1.13
A Sample Relational Database

1.14
SQL
• SQL: widely used non-procedural language
o 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’
o 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
o Language extensions to allow embedded SQL
o Application program interface (e.g., ODBC/JDBC) which allow SQL
queries to be sent to a database

1.15
Database 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.
o Business decision – What attributes should we record in the
database?
o 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

1.16
The Entity-Relationship Model
• Models an enterprise as a collection of entities and relationships
o Entity: a “thing” or “object” in the enterprise that is distinguishable
from other objects
 Described by a set of attributes
o Relationship: an association among several entities
• Represented diagrammatically by an entity-relationship diagram:

1.17
Other Data Models
• Object-oriented data model
• Object-relational data model

1.18
Database Application Architectures
(web browser)
Old Modern

1.19
Database Management System Internals
• Storage management
• Query processing
• Transaction processing

1.20
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:
o Interaction with the file manager
o Efficient storing, retrieving and updating of data
• Issues:
o Storage access
o File organization
o Indexing and hashing

1.21
Query Processing
1. Parsing and translation
2. Optimization
3. Evaluation

1.22
Query Processing (Cont.)
• Alternative ways of evaluating a given query
o Equivalent expressions
o 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
o Depends critically on statistical information about relations which the
database must maintain
o Need to estimate statistics for intermediate results to compute cost of
complex expressions

1.23
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.

1.24
Overall System Structure

1.25
History of Database Systems
• 1950s and early 1960s:
o Data processing using magnetic tapes for storage
 Tapes provide only sequential access
o Punched cards for input
• Late 1960s and 1970s:
o Hard disks allow direct access to data
o Network and hierarchical data models in widespread use
o 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
o High-performance (for the era) transaction processing

1.26
History (cont.)
• 1980s:
o Research relational prototypes evolve into commercial systems
 SQL becomes industry standard
o Parallel and distributed database systems
o Object-oriented database systems
• 1990s:
o Large decision support and data-mining applications
o Large multi-terabyte data warehouses
o Emergence of Web commerce
• 2000s:
o XML and XQuery standards
o Automated database administration
o Increasing use of highly parallel database systems
o Web-scale distributed data storage systems

Database System Concepts, 5th Ed.
©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
End of Chapter 1

1.28
Database 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
• Naïve users – invoke one of the permanent application programs that
have been written previously
o Examples, people accessing database over the web, bank tellers,
clerical staff

1.29
Database Administrator
• Coordinates all the activities of the database system
o has a good understanding of the enterprise’s information resources
and needs.
• Database administrator's duties include:
o Storage structure and access method definition
o Schema and physical organization modification
o Granting users authority to access the database
o Backing up data
o Monitoring performance and responding to changes
 Database tuning

1.30
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 (multiple processors and disks)
• Distributed

1.31
Object-Relational 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.

1.32
XML: 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

1.33
Figure 1.4

1.34
Figure 1.7

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