announcements. data management chapter 12 traditional file approach structure field record file ...
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Announcements
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Data Management
Chapter 12
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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
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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
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Traditional File Approach – cont’dAdvantages
Simplicity Efficiency Customization
Disadvantages Program/Data Dependency Data Redundancy Data Integrity
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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
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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
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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
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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
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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
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Major Database ProductsHierarchical
Focus, IMS, BtrieveNetwork
Adabas, ImageRelational
Access, DB2, dBase V, FoxPro, Paradox Oracle, Sybase, Rbase, Sql Server
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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
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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.
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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
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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
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Data WarehousingData warehouse
Collection of data that supports management decision making
Phases in Building a Data WarehouseExtraction PhaseCleansing PhaseLoading Phase
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Data MiningSelecting, exploring, and modeling data
to discover unknown relationshipsUse data modeling and “AI” techniques
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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?
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Discussion questionsDiscussion questions, pg 446-47: 17, 22,
25, and 32