meljun cortes computer information processing chapter 9 with notes

7/31/2019 MELJUN CORTES Computer Information Processing Chapter 9 With Notes

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OBJECTIVES Describe the types of data processing files

Describe the types of file organization

Data validation


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FILE, RECORD & FIELD

- Field Data item

e.g. student name

- Record A group of related data items or fields

e.g. student record

- File A collection of related records e.g. Student file


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ENTITY SET, ENTITY & ATTRIBUTES

- Attributes

Describe the properties of the entity (I.e. field)

- Entity

Which or when we store facts (i.e. records)

- Entity set A collection of logically related entities (i.e. file)


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1. Physical file :

Refers to how the data is stored i.e. the actual arrangement of

data in storage device

2. Logical file :

What a file contains & how the data should be processed

Logical File & Physical Files


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It is a field within the record which is used for locating &processing the recorde.g. student number

Key Field


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FILE LENGTH

Fixed-length records

Each record has the same length

Advantage: Easier to design

Disadvantage: Wasted storage space

Variable-length records

Each record does not have the same length Advantage: Saves storage space

Disadvantage: More difficult to design


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1. Writing :

The act of transferring a record from main memory to secondarystorage.

2. Insertion :

Adding a new record to an existing file.

3. Deleting : Removing a record from a file.

INFORMATION RETRIEVAL


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4. Updating : Making changes to the contents of a record to show the new

status of information.

5. Sorting :

Rearranging the records in a file for the purpose of producingordered reports.

6. Merging :

Combination of 2 or more files to produce a single output file.



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7. Matching : Where 2 or more output files are compared record

against record to ensure there is a complete set ofrecords for each key. Mismatched records arehighlighted for action.

8. Searching : Involves looking for a record with a certain key value

9. Appending :- Adding a record at the last available space of anexisting file



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The number of records that are changed as a result ofupdating when compared to the total number of recordsin the file.

HIT RATE

=

Volatility :

Measuring the number of additions and deletions in a file.

File growth No of records additions number of records deletions

number or records affected

total records on file

ACTIVITY RATIO (HIT RATE)


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1. Master file

Permanent or semi-permanent data

Used for reference and updating

Shows the current status of data

Never empty except at its time of creation

E.g. stock master file

TYPES OF DP FILES


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2. Transaction file

Contains source or transaction data

Used for updating master file

E.g. sales transaction file

3. Work file

Temporary file

Used for storing intermediate data for further processing

E.g. file used by sort utility

TYPES OF DP FILES


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4. Transition file

Temporary file for specific use

E.g. meter readings, customers detail for printout

5. Security & backup file

Extra copy of file against damage/loss

6. Audit file

Enables auditor to check correct functioning of computer based

procedures Keeps a copy of all transactions

TYPES OF DP FILES


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FILE ORGANISATIONS 4 Types

1. Serial

2. Sequential

3. Indexed-sequential

4. Random


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Simplest, not in any order

Placed record in next available space

Suitable for Unsorted transaction files

Print files

Dump files

Temporary data files

Access in order of records placed

SERIAL ORGANISATION


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SERIAL ORGANISATION

Advantages :

File design is simple

Efficient for high activity file

Effective use of low cost file media suitable for batch processing

Disadvantage :

File are to be processed from beginning to the end


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Predefined order

A designated field within the record is selected as basis inordering records

This key is also known as Record key orSimply key

Suitable for master file

Not for fast response on line enquiring systems

E.g. Payroll transaction file

SEQUENTIAL ORGANISATION


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SEQUENTIAL ORGANISATION

Advantages :

File design is simple

Efficient for high activity file

Effective use of low cost file media suitable for batched transactions

Disadvantage :

Entire file must be processed even if activity is low

Transactions required sorting


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Physical sequence to primary key

Builds an index separate from the data or

records Accessed randomly and sequentially

3 main parts

Prime (Home) area

Overflow area

Index area

INDEXED SEQUENTIAL

ORGANISATION


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INDEXED SEQUENTIAL

ORGANISATION When insufficient space in home area (prime area), overflow

area will be used

Overflow areas created at cylinder & track level

Access controlled by means of pointers

File reorganization to be done

Overflow records recovered & indexes rebuilt


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- Support three types of processing :

1. Sequential processing

2. Selective sequential processing/ Random access

3. Block is searched record by record until record is found/Direct access/ Dynamic access

INDEXED-SEQUENTIAL FILES


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Predictable relationship between record key &records location on disc

Not in sequence physically, scattered in random

Direct addressing

Key as physical address of record

Device dependent

RANDOM ORGANISATION


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INDEXED-SEQUENTIAL ORGANISATION

Advantages :

Transactions may be sorted or unsorted

Only the affected master records are processed during updating

Response time is reasonably fast

Facilities file enquiry Be processed sequentially and randomly

Disadvantage :

Each master file access requires index file access

Requires direct access storage devices (still costly)

Storage space required for indexes


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RANDOM ORGANIZATION

Predictable relationship between record key and record

location on disc

Records may be scattered in random

Direct addressing


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RANDOM ORGANIZATION

Key transformation techniques used

1. Division remainder method

Divide key value by an appropriate number

Remainder of division as address of record

Number used to divide is prime number

2. Mid Square Hashing

The key is squared, specified digits extracted from middle of the

result to yield address of the results


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RANDOM ORGANIZATION

3. Hashing By Folding

Key is divided into 2 or more parts which are then addedtogether

Truncation to bring result into required range of numbers


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RANDOM ORGANISATION

Advantages :

As index are not required, space and searching time are saved

Insertion and deletion or records can take place

Disadvantage :

Variable-length records are difficult to handle

Gaps in keys can caused wasted space

Synonym can occur

Allocation of efficient overflow areas is difficult


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Double punching method

Sight verification

DATA VERIFICATION


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Presence

Size

Range

Character check

Format

Reasonableness

Check digits

DATA VALIDATION


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Adequate program checkpoint/ restart facilities

File dumps

Generations of backup files

ERROR RECOVERY

meljun cortes computer information processing chapter 9 with notes

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