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Data Management

Chapter 12

Traditional File ApproachStructure

Field Record FileFixed

All records have common fields, and a field is the same size across all records

Variable Variable number of fields within a record Variable size for a field across records

Traditional File StructuresSequential Access

Batch ProcessMaster File Updates

Indexed Files Use an index to locate a specific record

Indexed-Sequential Way to store data sequentially and use indices to

access

Traditional File Approach – cont’dAdvantages

Simplicity Efficiency Customization

Disadvantages Program/Data Dependency Data Redundancy Data Integrity

Moving to Database Management System (DBMS)

AdvantagesReduced data redundancyApplication/data independenceBetter control

Security: Giving users different views addresses security issue

FlexibilityQueries: Request data from specified fields

Database ModelsThe Hierarchical Model

Records are related hierarchically -- each category is a subcategory of the next level up

Disadvantages of hierarchical databasesTo retrieve a record, a user must start at the root and

navigate the hierarchy.If a link is broken, the entire branch is lost.Requires considerable data redundancy

Database ModelsThe Network Model

Allows a record to be linked to more than one parent

Supports many-to-many (N:M) relationships Advantage of the network model

Reduced data redundancy Disadvantages of the network model

Complicated to build and difficult to maintainDifficult to navigate

Database ModelsThe Relational Model

Consists of tables; links among entities are maintained with foreign keys

Advantages of relational databasesSame advantages of a network database without the

complicationsEasier to conceptualize and maintainVirtually all DBMSs offered for microcomputers

accommodate the relational model

Comparison of Data ModelsHierarchical Network Relational

Conceptualization Moderately Easy

Difficult Easy

Ease of Design Very Difficult

Moderately Difficult

Difficult

Ease of Maintenance Difficult Very Difficult Easy

Data Redundancy High Low Low

Ease of Use Moderate Low High

Major Database ProductsHierarchical

Focus, IMS, BtrieveNetwork

Adabas, ImageRelational

Access, DB2, dBase V, FoxPro, Paradox Oracle, Sybase, Rbase, Sql Server

Components of Database Management Systems

The Schema Describes the structure of the database

The Data Dictionary (Metadata) Maintains all information supplied by the

developer when constructing the schemaData Definition Language (DDL)

Used to construct the schemaData Manipulation Language (DML)

Used to query the database

Advantages of using SQL

Structured Query Language (SQL)International standard DDL and DML for

relational DBMSUsers do not need to learn different DDLs and DMLs.SQL can be embedded in widely used 3rd generation

languages, increasing efficiency and effectiveness.Programmer not forced to rewrite statements since

SQL statements are portable.

Database ArchitectureDistributed Databases

ReplicationFull copy of the entire database is stored at all sites

Fragmentation (distributed)Parts of database are stored where they are most often

accessed

How to best support organizational needs with a DBMS?

Single, large, centralized repository Promotes maintenance and security As size of database grew, performance suffered Broadband still emerging, very expensive

Multiple smaller distributed databasesSome combination

Does everyone need access to real-time data?

db

db

db

Distributed

db

db

Data WarehousingData warehouse

Collection of data that supports management decision making

Phases in Building a Data WarehouseExtraction PhaseCleansing PhaseLoading Phase

Data MiningSelecting, exploring, and modeling data

to discover unknown relationshipsUse data modeling and “AI” techniques

Discussion Questions Distinguish the traditional file approach from the database

approach.  What are the primary differences in terms of how they store data?

What are the advantages and disadvantages of the following types of database models: hierarchical, network,  relational, and Object Oriented?

What alternative file-access methods are available to implement a database at the physical level? What factors should you consider when choosing among these alternative methods?

What is a DBMS and what are some of the key components of a DBMS?

Discussion questionsDiscussion questions, pg 446-47: 17, 22,

25, and 32