DATA
ORGANIZATION
DATA ORGANIZATION
•
Companies store vast quantities of data
•
There must be a means of saving and retrieving that
data efficiently
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Data organization is designed to facilitate the storage
an retrieval of specific data items.
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DATA ORGANIZATION COMPONENTS
DATA ORGANIZATION TERMS
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FILE ORGANIZATION
• Describes the access method for locating a record in a file.
• Each organization provides different efficiencies
• Types of file organization
• Sequential
• Direct
• Indexed
(sequential and non-sequential)
SEQUENTIAL RECORD ACCESS
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SEQUENTIAL RECORD ACCESS
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Records are ordered physically one after another
based on the key field.
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Useful when processing several records at one time.
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Can use a sequential or binary search or some other
search technique.
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Example: processing bills at end of the month.
DIRECT RECORD ACCESS
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DIRECT RECORD ACCESS
• Records stored at a particular location of a disk.
• Location of records are determined by hashing.
• Hashing
- an algorithm to convert the key field location
into a physical or logical address on the disk.
• Useful when processing specific records.
• Example: Accessing a customer’s current bill.
SEQUENTIAL VERSUS DIRECT ACCESS
Indexed
Supports both
Sequential
Useful for accessing
several records at once
Direct
Useful for accessing a
specific record
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INDEXED RECORD ACCESS
• In addition to the data, an index is maintained to identify the
location of a specific record.
•
Index: A table that lists the value of a field in each record
in a file and the record’s address.
• Two types
•
Indexed Sequential
•
Indexed Non-sequential
INDEXED RECORD ACCESS
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INDEXED SEQUENTIAL RECORD ACCESS
• A compromise between sequential and direct access.
• Stores records on the disk in physically sequential order.
• Also maintains an index (often a simpler block index.
• Can be accessed either directly or sequentially.
• Example: the telephone book
INDEXED NON-SEQUENTIAL RECORD ACCESS
• Record are not stored in any predefined order.
• Must maintain a full index (inverted index)
• Often used for accessing records in a relational database.
• Example: Books in a library.
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ACTIONS ON A DATABASE RECORD
• Create a new record (also called Insert)
• Read data from an existing record
• Update data on an existing record
• Delete an existing record
END
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