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1. DB2Database Management Systems Introduction to Database Systems 13/2/2012 DB2Dr.Suresh Sankaranarayanan

Database System Concepts by Abraham Silberschatz, 5 thEdition

Database Management Systems

Data Abstraction

Instances and Schemas

Data Models

Database Languages

Database Design

Database Architectures

History of Database systems

Database Management systemis a collection of interrelated data and a set of programs to access those data.

Data: stored representations of meaningful objects and events

Structured: numbers, text, dates

Unstructured: images, video, documents

Collection of data is usually referred to asdatabase

An environment that is bothconvenientandefficientto use

Database are widely used. Some of its applications are:

Banking: all transactions

Airlines: reservations, schedules

Universities:registration, grades

Credit Card Transactions: Purchases on credit cards and generation of monthly statements

Telecommunication: Keeping record of calls made, generating monthly bills, maintaining balances on prepaid calling, storing information about communication networks

Finance: Storing information about holdings, sales and purchase of financial instruments such as stocks and bonds

Sales: customers, products, purchases

Online retailers: order tracking, customized recommendations

Manufacturing: production, inventory, orders, supply chain

Human resources:employee records, salaries, tax deductions

Data Redundancy and inconsistency

Example is address and telephone number stored in a file containing savings and checking account records. This redundancy leads to higher storage and access cost.Also a changed customer address is reflected in savings accountbut not elsewhere in the system resulting in data inconsistency.

Accessing Data: Example is let us say bank officer wants to find names ofcustomers who live within the citys zip code say 78733. Asof here, the software was not designed to do this job . So here the officer is left with two choices: one is get list of all customers and extract the needed information manually. The second choice is ask the programmer to writethe necessary application program.

Data isolation: Data scattered in various file and files are in different format, it is difficult to write a new program to retrieve the appropriate data.

Concurrent Access: Consider say you and your friend are holder of an account say A which got an amount of say $2000.00. let us say both you and friend withdraws say $500 and $200 from the account at the same time.This results in incorrect result say 1500 or 1800 and not 1300. So to guard against it, some form of supervision must be maintained.

Security : In banking system, payroll personnel need see some part of database only that has information about various bank employees. As application programs are added in ad hoc manner, it is difficult to enforce such security problems

Integrity Problems: Data values stored in database must satisfy certain type of consistency constraint. For example say bank account should not have balance less than say $100.00. But if new constraints are to be added, it has to be enforced in the program.

Program-data independence

Planned data redundancy

Improved data consistency

Improved data sharing

Increased application development productivity

Enforcement of standards

Improved data quality

Improved data accessibility and responsiveness

Reduced program maintenance

Improved decision support

New, specialized personnel

Installation and management cost and complexity

Conversion costs

Need for explicit backup and recovery

Organizational conflict

CASE Toolscomputer-aided software engineering

Repositorycentralized storehouse of metadata

Database Management System (DBMS) software for managing the database

Databasestorehouse of the data

Application Programssoftware using the data

User Interfacetext and graphical displays to users

Data/Database Administratorspersonnel responsible for maintaining the database

System Developerspersonnel responsible for designing databases and software

End Userspeople who use the applications and databases

Database System is a collection of interrelated data

Set of programmes that allow users to access and modify the data

Purpose of database system is to provide users with an abstract view of data

Systemhides certain details of how the data are stored and maintained.

Three levels of data abstraction

Physical Level :

Lowest level of abstraction describes how data are actually stored.

Describes complex low level data structures in detail.

Logical level

Next higher level of abstraction

Describes what data are stored in database and what relationships exist among those data

View level:

Highest Level of Abstraction

Describes only part of the entire database.

Application programs hide details of data types.

Views can also hide information (such as an employees salary) for security purposes.

Database change over time as information is inserted and deleted

Instance:

Collection of Information stored in the database at a particular moment

Analogous to a value of variable in a program

Schema

Overall design of the database- logical structure is called Schema.

Corresponds to the variable declarations in a program.

Database systems have several Schemas according to the level of abstraction

a. Physical Schema: Database design at physical level

b. Logical Schema: Database design at logical level.

c. Subschemas:Several Schemas at view level that describe different viewsof the database

Data Independence: Ability to modify the Schema at one level without affecting the schema definition at another level.

Physical Data Independence

Ability to modify the physical schema without causing application programs to be rewritten.

Modifications at physical level are necessary to improve the performance

Logical Data Independence

Ability to modify the logical schema without causing application programs to be rewritten.

Modifications at logical level are necessary when logical structure of database is altered.

Data Models : Collection of tools for describing data, data relationships,data semantics anddata constraints

Data Models can be classified into four different categories:

Relational Model: Collection of tables to represent both data and relationships among those data

Entity- Relationship Model: Collection of basic objects called entities and relationship among these objects

Object Oriented Data model: Object Oriented data model can be seen as extending E-R model with notions of encapsulation, functions and Object identity. Combines the features of object oriented data model and relational data model

Semi structured Data model: Specification of data where individual data items of same type may have different set of attributes. XML is used to representsemi structured data.

Provides two languages- Data Definition Language(DDL) and Data Manipulation Language (DML)

DDL: Specify Database Schema

DML: Express Database queries and updates.

DDL and DML are not two separate languages

DDL and DML form parts of single database language such as SQL.

Relational database is based on two things :

a. Relational model

b. Collection of tables to represent both data and relationships among those data.

Includes DDL and DML

Employs SQL Language.

Relational data model is most widely useddata model and majority of database systems are based on relational data model.

A sample of relational database comprising of three tables is shown here.

Sql is not as powerful as a universal tuning machine

Some computations cannot be obtained by Sql query

These computations must be written in a host language like Cobol, C, C++ or Java with embedded Sql that access the data in database

Applications programs are ones that interact with the database in this fashion.

Application programs access the database in following two ways :

Language extensions to allow embedded SQL

Application program interface (e.g., ODBC/JDBC) which allow SQL queries to be sent to a database

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 Sciencedecision 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 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

In Two Tier application resides at the client machine that invokes the database system functionality at the server through query statements. ODBC and JDBC are used for interaction between client and server

In Three Tier, client machine acts as merely front end and contains no direct database calls. Instead client end communicates with the application server which in turn communicates with the database system to access data.

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

Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprises 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

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

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

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