File Organization Midterm

8/3/2019 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 files are important

for applications where data needs to be

accessed..... sequentially randomly using the index.


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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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Documents

File Organization Midterm