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ObjectivesObjectives Definition of termsDefinition of terms Describe the physical database design Describe the physical database design
processprocess Choose storage formats for attributesChoose storage formats for attributes Select appropriate file organizationsSelect appropriate file organizations Describe three types of file organizationDescribe three types of file organization Describe indexes and their appropriate useDescribe indexes and their appropriate use Translate a database model into efficient Translate a database model into efficient
structuresstructures Know when to use denormalizationKnow when to use denormalization
PurposePurpose - translate the logical - translate the logical description of data into the description of data into the technical technical specificationsspecifications for storing and for storing and retrieving dataretrieving data
Goal - create a design for storing Goal - create a design for storing data that will provide data that will provide adequate adequate performanceperformance and insure and insure database database integrityintegrity, , securitysecurity and and recoverabilityrecoverability
Usage analysis:140 purchased parts accessed per hour 80 quotations accessed from these 140 purchased part accesses 70 suppliers accessed from these 80 quotation accesses
Usage analysis:75 suppliers accessed per hour 40 quotations accessed from these 75 supplier accesses 40 purchased parts accessed from these 40 quotation accesses
Field: smallest unit of data in Field: smallest unit of data in databasedatabase
Field design Field design Choosing data typeChoosing data type Coding, compression, encryptionCoding, compression, encryption Controlling data integrityControlling data integrity
character (memo)character (memo) LONG – large numberLONG – large number NUMBER – positive/negative numberNUMBER – positive/negative number DATE – actual dateDATE – actual date BLOB – binary large object (good for BLOB – binary large object (good for
Default value – assumed value if no Default value – assumed value if no explicit valueexplicit value
Range control – allowable value Range control – allowable value limitations (constraints or validation limitations (constraints or validation rules)rules)
Null value control – allowing or Null value control – allowing or prohibiting empty fieldsprohibiting empty fields
Referential integrity – range control (and Referential integrity – range control (and null value allowances) for foreign-key to null value allowances) for foreign-key to primary-key match-upsprimary-key match-ups
Substitute an estimate of the missing Substitute an estimate of the missing value (e.g. using a formula)value (e.g. using a formula)
Construct a report listing missing valuesConstruct a report listing missing values In programs, ignore missing data unless In programs, ignore missing data unless
the value is significant (sensitivity the value is significant (sensitivity testing)testing)
DenormalizationDenormalization Transforming Transforming normalizednormalized relations into relations into
unnormalizedunnormalized physical record specifications physical record specifications Benefits:Benefits:
Can improve performance (speed) be reducing number of Can improve performance (speed) be reducing number of table lookups (i.e table lookups (i.e reduce number of necessary join queriesreduce number of necessary join queries))
Costs (due to data duplication)Costs (due to data duplication) Wasted storage spaceWasted storage space Data integrity/consistency threatsData integrity/consistency threats
Common denormalization opportunitiesCommon denormalization opportunities One-to-one relationship (Fig 6-3)One-to-one relationship (Fig 6-3) Many-to-many relationship with attributes (Fig. 6-4)Many-to-many relationship with attributes (Fig. 6-4) Reference data (1:N relationship where 1-side has data not Reference data (1:N relationship where 1-side has data not
used in any other relationship) (Fig. 6-5)used in any other relationship) (Fig. 6-5)
PartitioningPartitioning Horizontal Partitioning: Distributing the rows of Horizontal Partitioning: Distributing the rows of
a table into several separate filesa table into several separate files Useful for situations where different users need Useful for situations where different users need
access to different rowsaccess to different rows Three types: Key Range Partitioning, Hash Three types: Key Range Partitioning, Hash
Partitioning, or Composite PartitioningPartitioning, or Composite Partitioning Vertical Partitioning: Distributing the columns Vertical Partitioning: Distributing the columns
of a table into several separate filesof a table into several separate files Useful for situations where different users need Useful for situations where different users need
access to different columnsaccess to different columns The primary key must be repeated in each fileThe primary key must be repeated in each file
Combinations of Horizontal and VerticalCombinations of Horizontal and Vertical
Partitions often correspond with User Schemas (user views)
Partitioning (cont.)Partitioning (cont.) Advantages of Partitioning:Advantages of Partitioning:
Efficiency: Records used together are grouped togetherEfficiency: Records used together are grouped together Local optimization: Each partition can be optimized for Local optimization: Each partition can be optimized for
performanceperformance Security, recoverySecurity, recovery Load balancing: Partitions stored on different disks, Load balancing: Partitions stored on different disks,
reduces contentionreduces contention Take advantage of parallel processing capabilityTake advantage of parallel processing capability
Disadvantages of Partitioning:Disadvantages of Partitioning: Inconsistent access speed: Slow retrievals across Inconsistent access speed: Slow retrievals across
partitionspartitions Complexity: non-transparent partitioningComplexity: non-transparent partitioning Extra space or update time: duplicate data; access from Extra space or update time: duplicate data; access from
Purposely storing the same data in Purposely storing the same data in multiple locations of the databasemultiple locations of the database
Improves performance by allowing Improves performance by allowing multiple users to access the same data multiple users to access the same data at the same time with minimum at the same time with minimum contentioncontention
Sacrifices data integrity due to data Sacrifices data integrity due to data duplicationduplication
Best for data that is not updated oftenBest for data that is not updated often
A named portion of secondary memory allocated A named portion of secondary memory allocated for the purpose of storing physical recordsfor the purpose of storing physical records
Tablespace – named set of disk storage Tablespace – named set of disk storage elements in which physical files for database elements in which physical files for database tables can be storedtables can be stored
Extent – contiguous section of disk spaceExtent – contiguous section of disk space Constructs to link two pieces of data:Constructs to link two pieces of data:
Sequential storageSequential storage Pointers – field of data that can be used to locate Pointers – field of data that can be used to locate
related fields or recordsrelated fields or records
File OrganizationsFile Organizations Technique for physically arranging records of a file Technique for physically arranging records of a file
on secondary storageon secondary storage Factors for selecting file organization:Factors for selecting file organization:
Fast data retrieval and throughputFast data retrieval and throughput Efficient storage space utilizationEfficient storage space utilization Protection from failure and data lossProtection from failure and data loss Minimizing need for reorganizationMinimizing need for reorganization Accommodating growthAccommodating growth Security from unauthorized useSecurity from unauthorized use
Types of file organizationsTypes of file organizations SequentialSequential IndexedIndexed HashedHashed
Indexed File OrganizationsIndexed File Organizations Index – a separate table that contains Index – a separate table that contains
organization of records for quick retrievalorganization of records for quick retrieval Primary keys are automatically indexedPrimary keys are automatically indexed Oracle has a CREATE INDEX operation, and Oracle has a CREATE INDEX operation, and
MS ACCESS allows indexes to be created for MS ACCESS allows indexes to be created for most field typesmost field types
In some relational DBMSs, related records In some relational DBMSs, related records from different tables can be stored from different tables can be stored together in the same disk areatogether in the same disk area
Useful for improving performance of join Useful for improving performance of join operationsoperations
Primary key records of the main table are Primary key records of the main table are stored adjacent to associated foreign key stored adjacent to associated foreign key records of the dependent tablerecords of the dependent table
e.g. Oracle has a CREATE CLUSTER e.g. Oracle has a CREATE CLUSTER commandcommand
1. Use on larger tables1. Use on larger tables2. Index the primary key of each table2. Index the primary key of each table3. Index search fields (fields frequently 3. Index search fields (fields frequently
in WHERE clause)in WHERE clause)4. Fields in SQL ORDER BY and GROUP 4. Fields in SQL ORDER BY and GROUP
BY commandsBY commands5. When there are >100 values but not 5. When there are >100 values but not
when there are <30 valueswhen there are <30 values
Rules for Using Indexes Rules for Using Indexes (cont.)(cont.)
6. DBMS may have limit on number of 6. DBMS may have limit on number of indexes per table and number of indexes per table and number of bytes per indexed field(s)bytes per indexed field(s)
7. Null values will not be referenced 7. Null values will not be referenced from an indexfrom an index
8. Use indexes heavily for non-volatile 8. Use indexes heavily for non-volatile databases; limit the use of indexes for databases; limit the use of indexes for volatile databasesvolatile databases
Why? Because modifications (e.g. inserts, Why? Because modifications (e.g. inserts, deletes) require updates to occur in index filesdeletes) require updates to occur in index files