Database_Management.ppt 333KB Mar 29 2010 04:55:20 AM

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Database Management

Foundations of Information Systems

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Chapter Objectives

• Specify the elements of the data hierarchy.

• Understand what can be accomplished with files and

what the limitations of a file-based environment are.

• Understand the advantages of a database

environment and the role of a database management

system (DBMS).

• Specify the three levels at which data are defined in

databases.

• Compare the three data models.

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Chapter Objectives, cont.

• Understand the role of the data dictionary.

• Explain the components of information

resource management.

• Describe the developmental trends in

database management, including distributed

databases, data warehouses, and

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Hierarchy of Data

• Data are the Principal Resources of an

Organization

• Data Stored in Computer Systems form

a Hierarchy

– Extending from a Single Bit to a Database

– The Major Record Keeping entity of a firm

– Each higher rung of this hierarchy is

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Hierarchy of Data

• Data are logically organized into:

• 1. Bits (Characters)

• 2. Fields

• 3. Records

• 4. Files

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Hierarchy of Data

• Bit (Character)

– The smallest unit of data representation

– Value of a Bit may be 0 or 1

– 8 Bits make a Byte which can represent a

character or a special symbol in a

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Hierarchy of Data

• Field

– A grouping of characters

– A data field represents an attribute,

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Hierarchy of Data

• Record

– A collection of attributes that describe a

real world entity

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Hierarchy of Data

• File

– A group of related records

– Classified by the application for which

they are used

• Example: Employee File

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Hierarchy of Data

• Database

– An integrated collection of logically related records or

files

– Consolidates records previously stored in separate files

into a common pool of data records that provides data

for may applications

– The Data is managed by systems software called

Database Management Systems (DBMS)

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Hierarchy of Data Organization in

Computer Storage

Hierarchy of Data Organization in

Computer Storage

Component of Data Organization Logical Components Physical (Storage) Components Database File Record Field (attribute) Byte Bit Example SUPPLIERS PARTS SHIPMENTS SUPPLIERS

NO. NAME STREETADDRESS CITY ST ZIP 13 Gasket Co. 50 Oak Tifflin OH 44883

3251 Reliable Supp. 11 Cedar Teaneck NJ 07666 13 Gasket Co. 50 Oak Tifflin OH 44883

Reliable Suppliers

01000001 (represents “A” in the ASCII-8 character code) 0

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File Environment and Its

Limitations

• File Organization

– Data files are organized so as to facilitate

access to records and to ensure efficient

storage

• A Tradeoff between these two requirements

generally exists

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File Environment and Its

Limitations

• Access to a record for reading it is the essential

operation on data

• 1. Sequential Access

– Records are accessed in the order they are stored

– The main access mode only in Batch Systems where files are used and updated at regular intervals

• 2. Direct Access

– Required by On-Line Processing

– A Record can be accessed without including the records between it and the beginning of the file

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File Environment and Its

Limitations

• File Organization Methods

• 1. Sequential Organization

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Limitations

• Sequential Organization

– Records are physically stored in a specified order according to a key field in each record

– Advantages

• Fast

• Efficient for dealing with large volumes data that need to be processed periodically (batch system)

– Disadvantages

• Requires that all new transactions be sorted into the proper sequence for sequential access processing

• Locating, Storing, Modifying, Deleting, or Adding Records in the file requires rearranging the file

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File Environment and Its

Limitations

• Indexed Sequential Organization

– Records are physically stored in

sequential order on a magnetic disk or

other direct access storage device based

on the key field of each record

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Limitations

• Direct Organization

– Provides the fastest direct access to records

– Records do not have to be arranged in any particular

sequence on storage media

– Computers must keep track of the storage location

of each record using a variety of direct organization

methods to retrieve data

– New transactions’ data does not have to be sorted

– Processing that requires immediate responses or

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File Environment and Its

Limitations

• Limitations of a File Oriented

Environment

– Fair amount of data redundancy

– Example of Three Systems

• Supplier

• Shipment

• Inventory

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Database Environment

• A Database is an organized collection of

interrelated data that serves a number of

applications in an enterprise.

– Stores both the values of various entities

and their relationships

– Managed by a Database Management

System DBMS

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Database Environment

• DBMS

• Helps organize data for effective access

by a variety of users with different access

needs and for efficient storage

• Makes it possible to create, access,

maintain, and control databases

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Database Environment

• Advantages of a Database Management

Approach

• Avoiding uncontrolled data redundancy

and preventing inconsistency

• Program-Data independence

• Flexible access to shared data

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A Database Environment

Reports

Reports DBMS Application

Program A

Application Program X End Users

Query

Update

Database

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Levels of Data Definition in

Databases

• User view of a DBMS is the basis for

modeling steps

• Data models define the logical

relationships among the elements to

support the basic process

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Levels of Data Definition in

Databases

• DBMS defines a database

• Schema

– Overall logical view of the relationships between data in a database

• Subschema

– Logical view of data relationships needed to support specific end user applications to access the database

• Physical

– How data is physically arranged, stored, and accessed on the magnetic disks and other secondary storage devices of a

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Levels of Data Definition in

Databases

• DBMS provides the language, DDL

Data Definition Language to define the

databases on the three levels (Schema,

Subschema, and Physical), and the

DML Data Manipulation Language to

access records, change values of

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Data Models or How to

Represent Relationships

Between Data

• Data Model is a method for organizing databases

on the logical, schema, and subschema levels.

• The main concern is how to represent

relationships among database records

• Relationships are based on logical data structures

or models

• DBMS are designed to provide end users with

quick, easy access to information in the

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Data Models or How to Represent

Relationships

Between Data

• Data Model Structures

• Hierarchical

• Network

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Relationships

Between Data: Hierarchical

• Used by early mainframe DBMS

• Relationships between records form a hierarchy or tree-like structure.

• Records are dependent and arranged in multilevel structures of one root record and any number of subordinate levels.

• Relationships among the records are one-to-many as each data element is related only to one element above it.

• The data element or record at the highest level is the root element. Any data element can be accessed by moving

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Data Models or How to Represent

Relationships

Between Data: Hierarchical

• Advantages

– Ease with which data can be stored and retrieved in structured, routine types of transactions

– Ease with which data can be extracted for reporting purposes – Routine types of transaction processing are fast and efficient.

• Disadvantages

– Hierarchical one-to-many relationships must be specified in advance and are not flexible.

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A Hierarchical Database

CLASS

MIS 101 1 525 MWF 10-11 a.m.

PROFESSOR PROFESSOR PROFESSOR NUMBER PROFESSOR NUMBER

221 Turkel 02579 Young

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Data Models or How to Represent

Relationships

Between Data: Network

• Can represent more complex logical

relationships and is used by mainframe

DBMS packages

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Relationships

Between Data: Network

• Advantages

– More flexible than the hierarchical model

– Ability to provide sophisticated logical relationships among the records

• Disadvantages

– Network many-to-many relationships must be specified in advance

– User is limited to retrieving data that can be access using the established links between records

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PROFESSOR PROFESSOR 221 PROFESSOR NUMBER PROFESSOR NAME

MIS 101 1 525 MWF 10-11 a.m.

COURSE NUMBER SECTION ROOM NUMBER MEETING DAYS MEETING HOURS 01171 STUDENT NUMBER STUDENT NAME Turkel Johnson STUDENT STUDENT

Links to Records of Other Classes Taught by This Professor

Links to Records of Other Classes Taken by This Student

Links to Records of Other Students Taking This Class

A Network Database

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Relationships

Between Data: Relational

•

contain common fields

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Relationships

Between Data: Relational

• Advantages

– Flexible in that ad hoc information request can be handled – Easy for programmers

– End users can use Relational Structures with little effort or training.

– Easier to maintain than the hierarchical and network models

• Disadvantages

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Relational Databases

• A collection of tables that is relatively easy to use and understand offering flexibility for the data and ability to modify

• All records in a relational database must have a unique primary key

• Relational Systems support three principal operations on tables without any predefined access paths

• Select- from a specified row that satisfies a given condition • Project- selects the attribute values

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Relational Databases

• The power of the relational model

derives from the join operation.

– Records are related through a join

operation rather than links so that a

predefined access path is not needed

– The join operation is time consuming

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SQL- A Relational Query

Language

• International standard access language fro defining and

manipulating data in databases

• Data-Definition-and-Management Language for DBMS

and some nonrelational ones

• SQL is used an independent query language to define

objects in a database, enter, and access the data

• Embedded SQL is for programming in procedural

languages (host) such as C, COBOL, PL/1, PL/SQL to

access from an application program

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SQL- A Relational Query

Language

• Principal Facilities of SQL

• Data Definition

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Designing a Relational

Database

• Database design progresses from the design of the

logical of the schema and the subschema to the physical

level.

• Logical Design or Data Modeling is to design the

schema and the subschema.

• A relational database consists of tables (relations)

describing the attributes of a particular class of entities.

• Logical Design begins with identifying the entity classes

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Database

• Entity-Relationship (E-R) Diagrams

are used to perform data modeling.

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Database

• Normalization is the simplification of the

logical view of data in relational databases

meaning that all fields contain single data

elements, distinct records, and each table

describes only a single class of entities.

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Database

• Physical Design is after the Logical Design of the

database.

• Fields are specified as to their length and the

nature of the data (numeric, characters).

• A principal objective is to minimize the number of

time consuming disk accesses that are necessary in

order to answer typical database queries.

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The Data Dictionary

• A software module and database

containing descriptions and definitions

of the structure, data elements,

interrelationships, and other

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The Data Dictionary

•

Schema, Subschemas, and Physical Schema

•

Which applications and users may retrieve and/or modify

the specific data

•

Cross reference information such as which programs use

what data and the users receive particular reports

•

Where individual data elements originate, and who is

responsible for maintaining the data

•

Standard naming conventions for database entities

•

Integrity rules for the data

•

Where the data are stored in geographically distributed

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The Data Dictionary

• Contains all the data definitions and

information necessary to identify data

ownership

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Managing the Data Resource

of an Organization

• Database technology enables organizations to

control their data as a resource, but it does not

automatically produce organizational control of data

• Components of Information Resources Management:

Organizational and Technical Means

• Ensure that a firm systematically accumulates data

in its databases

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of an Organization

• Principal Components of Information

Resource Management

• Organizational Processes

– Information planning and data modeling

• Enabling Technologies

– DBMS and a Data Dictionary

• Organizational Functions

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of an Organization

• Database Administration Functional

Units to Manage the Data

• Data Administrator (DA)

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Managing the Data Resource of an

Organization:

Data Administrator

• Person who has the central responsibility for an organization’s data

• Establish policies and specific procedures for collecting, validating, sharing, and inventorying data to be stored and

databases and for making information accessible to members of the organization and possible persons outside of it

• Data administration is a policy making function and the DA should have access to senior corporate management.

• Key person involved in the strategic planning of the data resource

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Managing the Data Resource of an

Organization:

Database Administrator

• A specialist responsible for maintaining standards for the development, maintenance and security of an organization’s databases

• Creating the databases and carrying out the policies of the data administrator

• In large organizations, the DBA function is performed by a group of professionals; in a small firm, a programmer/ analyst may

perform the DBA function, while one of the managers acts as the DA.

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Managing the Data Resource of

an Organization

• Joint Responsibilities of the DA and DBA

• Maintaining the Data Dictionary

• Standardizing names and other aspects of data

definition

• Providing Backup

• Provide security and privacy for the data stored

in the database

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Developmental Trends in

Database Management

• Distributed Databases

• Data Warehousing

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Developmental Trends in

Database Management

• Distributed Databases

– Spread across several physical locations

– Data are placed where they are used most often – Entire database is available to each authorized user – Local work groups (LAN)

– Departments at regional offices (WAN)

• Branch offices, manufacturing plants, and other work sites

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Developmental Trends in

Database Management

• Data Warehouse Databases

– Stores data from current and previous years that has been extracted from operational and management databases

– Central source of data

– Standardized and integrated for use by managers and other end user professionals

– Objective of a corporate data warehouse

• To continually select data from the operational databases • Transform the data into a uniform format

• Open the warehouse to the ends through a friendly and consistent interface

– Data mining

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Developmental Trends in

Database Management

• Systems supporting a data warehouse • Extract and Prepare Data

– The first subsystem extracts the data from the operational systems – Many are older legacy systems that get “scrubbed” by removing

errors and inconsistencies

• Store Data in the Warehouse

– The second support component is the DBMS that will manage the warehouse data.

• Provide Access and Analysis Capabilities

– The third subsystem is made up of the query tools to access the data – Includes OLAP (OnLine Analytical Processing) and other DSS tools

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Developmental Trends in

Database Management

• Object-Oriented and Other Rich Databases

– With expanded capabilities of information technology, the content of databases is becoming richer

– Traditional databases include largely numerical data or short fragments of text organized into well structured records

– As processing and storage capabilities expand with growing telecommunications, the knowledge is supported with rich data

– Geographic Information Systems – Object-Oriented Databases

– Hypertext and Hypermedia Databases

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Tele-communications communications Network Network

Site 1 Site 3

Site 2

Users have access to the entire database over the network

Database Fragment 3 Database Fragment 1 Database Fragment 2 . . . . . .

A System with a Distributed Database

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Bit Byte Field Record File Primary Key Database

Access (to a record) Sequential Access Direct Access Sequential File Indexed-Sequential File Direct File Database Management System (DBMS) Program-Data Independence Schema Subschema Bit Byte Field Record File Primary Key Database