databases and processing modes

8/3/2019 Databases and Processing Modes

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Databases and Processing

Modes


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Fundamental Data StorageConcepts and Definitions

What is an entity?

An entity is something about whichinformation is stored.

What are some examples of entities?

employees

inventory items

customers


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Computers store data by organizingsmaller units of data into large, moremeaningful ones.

A fieldis the smallest element of datastorage.

A number of fields are grouped together toform a record, which is a collection of datavalues that describe specific attributes ofone entity.


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Related records are grouped together toform a file.

What is an example of a file?

the accounts receivable file

Files containing related data are combinedto form a data base.


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Data base

File

Record

Field



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Accounts Receivable File

2 Entities2 Records

Attributes

Customer Customer Creditnumber name Address limit Balance

Datavalues

301 ABC Co. Box 5 1,000 400555 XYZ Co. Box 9 6,000 2,000

Individual fields


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Types of Files

Two basic types of files are used to storedata.

1 The master file, which is conceptually similar

to a ledger in a manual system.

2 The transaction file, which is conceptuallysimilar to a journal in a manual system.


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1 9 8 2

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1 9 8 61 9 8 5

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File Access and Organization

All computer systems must have someformalized means of organizing data sothat it can be accessed easily and

efficiently.


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Accessing Individual Records

Records are typically updated, stored, andretrieved using an identifier called aprimarykey. The primary key must be

unique for each entity.What are some examples of theappropriate primary key for a record?

customer number for the customer file invoice number for the invoice file


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Accessing Individual Records

A secondary key is another field used toidentify a record.

Secondary keys do not uniquely identifyindividual records, but identify a group ofrecords.

What are some examples of secondarykeys?

invoice due date

zip code


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File Organization

File organization refers to the way data arestored on the physical storage media.

There are three basic ways that files areorganized.

1 Sequential access files

2 Indexed sequential access method (ISAM) files

3 Direct access files


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File Organization

Sequential access files store records inorder according to their primary key (e.g.,customer numbers from 00001 to 99999).

Indexed sequential access method (ISAM)files store records in sequential order, butalso have an index that links primary keys

with their physical addresses.


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File Organization

Direct access files store records in noparticular order.

A mathematical algorithm is applied to theprimary key to determine the physicaladdress at which to store that record.


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Data Processing

The most common data processing activityis data maintenance.

Data maintenance is the periodicprocessing of transactions to updatestored data.

What are some commonly used types ofdata maintenance?


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Data Processing

Additionsinsert new records into a masterfile.

Deletionsremove records from a masterfile.

Updatesrevise current balances in master

files.

Changesmodify the data values of otherfields in master files.


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Batch Processing

Batch processing is updating master filesperiodically to reflect all transactions thatoccurred during a given time period.

The master file is updated at set times orwhenever a manageable number oftransactions are gathered.

Transaction data can either be entered asa batch or as each transaction occurs.


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Master

file

Group source documents into batches.

Batch Processing


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On-line Batch Processing

Master

file

Enter transactions into system as they occur.


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On-line, Real-Time Processing

In on-line, real-time processing, thecomputer captures data electronically,...

edits it for accuracy and completeness, and...

immediately processes it.

The computer also processes informationrequests from users.


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On-line, Real-Time Processing

Master

file

Enter transactions into system as they occur.


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Advantages of Each Method

The main advantage of batch processingwas efficiency in processing.

On-line data entry is more accurate thanperiodic batch input because the systemcan refuse incomplete of erroneousentries.

Real-time processing ensures that theinformation in master files is alwayscurrent.

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