Databases and Processing Modes

Fundamental Data Storage Concepts and Definitions What is an entity? An entity is something about which information is stored. What are some examples of entities? – employees – inventory items – customers

Fundamental Data Storage Concepts and Definitions What are attributes? Each entity has attributes, or characteristics of interest, which need to be stored. What are some examples? – employee pay rates – customer addresses

Fundamental Data Storage Concepts and Definitions Computers store data by organizing smaller units of data into large, more meaningful ones. A field is the smallest element of data storage. A number of fields are grouped together to form a record, which is a collection of data values that describe specific attributes of one entity.

Fundamental Data Storage Concepts and Definitions Related records are grouped together to form a file. What is an example of a file? –the accounts receivable file Files containing related data are combined to form a data base.

Data base File Record Field Fundamental Data Storage Concepts and Definitions

Accounts Receivable File 2 Entities 2 Records Attributes Customer Customer Credit number name Address limit Balance Data values 301ABC Co. Box 51, XYZ Co. Box 96,000 2,000 Individual fields

Types of Files Two basic types of files are used to store data. 1The master file, which is conceptually similar to a ledger in a manual system. 2The transaction file, which is conceptually similar to a journal in a manual system.

File Access and Organization All computer systems must have some formalized means of organizing data so that it can be accessed easily and efficiently.

Accessing Individual Records Records are typically updated, stored, and retrieved using an identifier called a primary key. The primary key must be unique for each entity. What are some examples of the appropriate primary key for a record? –customer number for the customer file –invoice number for the invoice file

Accessing Individual Records A secondary key is another field used to identify a record. Secondary keys do not uniquely identify individual records, but identify a group of records. What are some examples of secondary keys? – invoice due date – zip code

File Organization File organization refers to the way data are stored on the physical storage media. There are three basic ways that files are organized. 1Sequential access files 2Indexed sequential access method (ISAM) files 3Direct access files

File Organization Sequential access files store records in order according to their primary key (e.g., customer numbers from to 99999). Indexed sequential access method (ISAM) files store records in sequential order, but also have an index that links primary keys with their physical addresses.

File Organization Direct access files store records in no particular order. A mathematical algorithm is applied to the primary key to determine the physical address at which to store that record.

Data Processing The most common data processing activity is data maintenance. Data maintenance is the periodic processing of transactions to update stored data. What are some commonly used types of data maintenance?

Data Processing Additions insert new records into a master file. Deletions remove records from a master file. Updates revise current balances in master files. Changes modify the data values of other fields in master files.

Batch Processing Batch processing is updating master files periodically to reflect all transactions that occurred during a given time period. The master file is updated at set times or whenever a manageable number of transactions are gathered. Transaction data can either be entered as a batch or as each transaction occurs.

Master file Group source documents into batches. Batch Processing

On-line Batch Processing Master file Enter transactions into system as they occur.

On-line, Real-Time Processing In on-line, real-time processing, the computer captures data electronically,... –edits it for accuracy and completeness, and... –immediately processes it. The computer also processes information requests from users.

On-line, Real-Time Processing Master file Enter transactions into system as they occur.

Advantages of Each Method The main advantage of batch processing was efficiency in processing. On-line data entry is more accurate than periodic batch input because the system can refuse incomplete of erroneous entries. Real-time processing ensures that the information in master files is always current.