Download - File Organization Midterm
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FILOR
FILE ORGANIZATION
INTRODUCTION
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FILE DESIGN
The study of file structures involves the investigation of the
data structures used to organize a large collection of datainto one or more external files that are stored on secondary
storage devices.
FILE
- is a collection of related data
Example:
payroll file
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FILE ORGANIZATION
-refers to the way in which records are stored in an external
file- refers to the data structures used for organizing the data
FOUR COMMON FILE ORGANIZATIONS
1. Sequential2. Random
3. Indexed sequential
4. Multikey
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SEQUENTIAL FILE ORGANIZATION
- records are written consecutively- file are stored in ascending or descending order according
to a key field.
ADVANTAGE:
- easier to maintain than other organizations
especially interms of adding and deleting records
RANDOM FILE ORGANIZATION
- implies a predictable relationship between the key used to
identify an individual record and that record's location in anexternal file.
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INDEXED SEQUENTIAL FILE ORGANIZATION
combines sequential access and ordering with the
capabilities of random access.
TWO PARTS OF INDEXED SEQUENTIAL FILE:
1. A collection of records stored in contiguous locations
within blocks in a relative file and ordered by a key field.
2. An index (a hierarchical structure of record keys and
relative block numbers) to the file of ordered records.
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MULTIKEY FILE ORGANIZATION
allows access to a data file by several different key fields.
Example:
Library file that requires access by author and by subject
matter and title.
Multikey organization is being implemented using B-trees.
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DATA FILE TYPES
1. Master file
2. Transaction file
3. Table file
4. Report file5. Control file
6. History file
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MASTER FILE
contains records of permanent data that are updated by
adding, deleting, or changing
Example:
Payroll master file contains an employee's social security
number, the rate pay, marital status, number of exemptionsclaimed, and year-to-date deductions and earnings.
TRANSACTION FILE
contains records of changes, additions, and deletions madeto a master file.
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TABLE FILE
consists of a table of data, such as a price list, a tax rate
table, or some other form or reference data that is static and
is referenced by one of the other type of files.
REPORT FILE
contains information that has been prepared for the user.
CONTROL FILE
is small and contains information concerning a particular
maintenance run, such as the date of the run; the number
of master records read, added, deleted, and written; andthe number of transaction records read, processed and in
error
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HISTORY FILE
consists of all the backup master files, transaction files,and control files from past runs.
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FILE CHARACTERISTICS
1. Activity of a file
is a measure of the percentage of existing master
records changed during a maintenance run.
2. Volatility of a file
is a measure of the number of records added and
deleted compared to the original number of records.
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FILE MANIPULATION
1. Queries
involve searching a file for records containing certain
values in particular key fields.
2. Merging
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TYPES OF FILE ORGANIZATION
Serial
Sequential Indexed Sequential
Direct Access /Random Access
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Serial File Organization
A collection of records
No particular sequence
Cannot be used as master
Used as temporary transaction file
Records stored in the order received
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Sequential File Organization
A collection of records
Stored in key sequence
Adding/deleting record requires making
new file
Used as master files
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Sequential file
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Advantages
Simple file design
Very efficient when most of the records
must be processed e.g. Payroll
Very efficient if the data has a naturalorder
Can be stored on inexpensive devices like
magnetic tape.
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Disadvantages
Entire file must be processed even if a
single record is to be searched.
Transactions have to be sorted before
processing Overall processing is slow
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Direct (Random) File Organization
Records are read directly from or written
on to the file.
The records are stored at known address.
Address is calculated by applying amathematical function to the key field.
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Direct (Random) File Organization
A random file would have to be stored on
a direct access backing storage medium
e.g. magnetic disc, CD, DVD
Example : Any information retrieval
system. Eg Train timetable system.
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Advantages
Any record can be directly accessed.
Speed of record processing is very fast.
Up-to-date file because of online
updating. Concurrent processing is possible.
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Disadvantages
More complex than sequential
Does not fully use memory locations
More security and backup problems
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Indexed sequential file
Each record of a file has a key field whichuniquely identifies that record.
An index consists of keys and
addresses. An indexed sequential file is a
sequential file (i.e. sorted into order of akey field) which has an index.
A full index to a file is one in which thereis an entry for every record.
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Indexed sequential file
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Indexed sequential file
Indexed sequential files are important
for applications where data needs to be
accessed..... sequentially randomly using the index.
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Indexed sequential file
An indexed sequential file can only be
stored on a random access device
e.g. magnetic disc, CD.
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Advantages
Provides flexibility for users who need
both type of accesses with the same file
Faster than sequential
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Disadvantages
Extra storage space for the index is
required
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Data Transfer Speed
Problem 1: How long does it take to send 500 MB (in
total) data file over a 1.5Mbps connection? (assuming
ideal circumstances)
time = file-size /speed
Convert to same units e.g. seconds, Mbits and Mbps.
file-size = 500MB = 500 x 8(data) = 4000Mb
speed = 1.5Mbps
time-in-seconds = file-size / speed = 4000 / 1.5 =
2666.67 seconds = 44 minutes and 26.67 seconds
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Problem 2: How fast a connection is
required to transfer a 1.2GB video (in
total) in 10 minutes? (assuming ideal
circumstances) ?
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