Week 3-1 Databas Introduction_temp

8/7/2019 Week 3-1 Databas Introduction_temp

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Database

Week 3-1

Introduction of Database Management Systems


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Data Warehouse

Customer No. Name Address Membership

Product No. Product Name Price Description

External Source

MySQL

ERD

Data Mining

Competitive Advantage Performance

Good Business Decision Better Understanding


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Introduction of DBMS

Database management system (DBMS)

Consists of a collection of interrelated data and a set of programs toaccess that data

Designed to manage large bodies of information

Management of data involves Definition of structures for the storage of information

Provision of mechanisms for the manipulation of information

Provide safety of the information stored Collection of data

is referred to as the database

Contains information about one particular enterprise

Goal of DBMS

To provide an environment that is both convenient and efficient to use inretrieving and storing database information

DBMS vs. typical file processing system File processing system

Permanent records are stored in various files

Number of different application programs are written to extract recordsfrom and add records to the appropriate files


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Purpose of Database Systems

Data redundancy and inconsistency higher storage and access cost

Difficulty in accessing data

Conventional file-processing environments do notallow needed data to be retrieved in a convenient and

efficient manner Data isolation

Concurrent access anomalies

Security problems

Not every user should be able to access all the data Integrity problems

Data values stored in the database must satisfycertain types of consistency constraints


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Data Abstraction

Database management systems is a collectionof interrelated files and a set of programs that

allow users to access and modify these files

Major purpose of DBMS is to provide users with

an abstract view of the data System hides certain details of how the data

is stored and maintained

Complexity of data structures is hidden from

users through several levels of abstraction


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The Three Levels of Data Abstraction

Physical level

How the data are actually stored Complex low-level data structure are described in detail

Conceptual level

What data are actually stored

Entire database is described in terms of a small number of

relatively simple structure View level

Describes only part of the entire database to further simplify usersinteraction with the system

View 1 View 1 View 1

Conceptual Level

Physical Level


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Instances and Schemes

Database change over time as information is insertedand deleted

Instance

The collection of information stored in the database ata particular moment in time

Database Scheme The overall design of the database

Schemes are changed infrequently

Database systems have several schemes, partitioned

according to the levels of abstraction In general, database systems support one physical

scheme, one conceptual scheme and severalsubschems


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Data Independence

Data independence The ability to modify a scheme definition in one level

without a scheme definition in the next higher level

Physical data independence

The ability to modify the physical scheme without

causing application programs to be rewritten Modifications at the physical level are occasionally

necessary in order to improve performance

Logical data independence

The ability to modify the conceptual scheme withoutcausing application programs to be rewritten

Modifications at the conceptual level are necessarywhenever the logical structure of the database isaltered


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Data Definition Language

Data definition language A set of definitions which are expressed by a

special language and specify database

scheme

The result of compilation of DDL statements isa set of tables which are stored in a special

file called data dictionary

Data dictionary

A file that contains metadata (data about data)


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Data Manipulation Language

Data Manipulation The retrieval of information stored in the database

The insertion of new information into the database

The deletion of information from the database

The modification of data stored in the database

Data Manipulation Language (DML)

Enables users to access or manipulate data asorganized by the appropriate data model

Procedural DML / Nonprocedural DML Depending on whether DML require a user to specify what

data is needed and how to get it

Query A statement requesting the retrieval of information

Query Language

Portion of a DML that involves information retrieval


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Database Manager

Database Manager

A program module which provides the interface between the low-level data stored in the database and the application programsand queries submitted to the system

Interaction with the file manager

Translates the various DML statements into low-level file system

commands Responsible for actual storing, retrieving, and updating of data in

the database

Integrity enforcement

Determine whether updates to the database result in theviolation of the constraint

Security enforcement

Backup and recovery

Concurrency control


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Database Administrator

Database administrator A person having central control of both data and

programs accessing that data

Functions of the database administrator

Scheme definition Translated by the DDL compiler to a set of tables that are

permanently stored in the data dictionary

Storage structure and access method definition

Scheme and physical organization modification

Granting of authorization for data access

Integrity constraint specifications


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Overall System Structure

Functional components of a database system

File manager Manages the allocation of space on disk storage and the data

structures used to represent information stored on disk

Database manager Provides the interface between the low-level data stored in the

database and the application programs and queries submitted to the

system Query processor

Translates statements in a query language into low-levelinstructions that the database manager understands

Attempts to transform a users request into an equivalent but moreefficient form

DML precompiler Converts DML statements embedded in an application program to

normal procedure calls in the host language

DDL compiler Converts DDL statements to a set of tables containing metadata


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Overall System Structure (2)

Several data structures are required as part ofthe physical system implementation

Data files

Stores the database itself

Data dictionary Stores metadata about the structure of the

database

Indices

Provide for fast access to data items holding

particular values


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System Structure

data dictionary

data files

file manager

DDL compilerquery

processor

database

manager

application

programs

object code

DML precompiler

application

interfaces

application

programsquery

database

scheme

naive users application programmers sophisticated users database administrator

disk storage

Week 3-1 Databas Introduction_temp

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