Computers14 Ch6
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There are three main methods for organizing data files: sequential, direct, and indexed. Sequential organization stores records in order by a key field, requiring reading all prior records to access a specific one. Direct organization allows random access via a record key and a formula to derive the disk address. Indexed organization stores records sequentially but also has an index containing the record key and associated address for direct access. Data can be processed via batch or transaction processing. Batch processing collects transactions into batches to update the master file periodically, while transaction processing handles each transaction immediately as it occurs.
Computers14 Ch6
- 1. Storage and Multimedia Chapter 6 B.M.H
- 2. Index How data is organized How to access the file File organization Sequential file organization Direct file organization Indexed file organization How to process the file Batch processing Transaction processing
- 3. How data is organized Raw data is organized into Characters Fields Records File Databases
- 4. How data is organized Characters the smallest element A letter, digit, or special character Fields A set of related characters Records A collection of related fields
- 5. How data is organized File A collection of related records Databases A collection of interrelated files stored together with minimum redundancy
- 6. How data is organized Key A field of particular interest A unique identifier for a record Ex. custom number, product number, social security number,
- 7. The File Plan The plan considered by some computer professional How to access the file File organization How to process the file
- 8. How to access the file
- 9. File organization Three major methods of organizing data files in secondary storage Sequential file organization Direct file organization Indexed file organization
- 10. Sequential File Organization Records are arranged sequentially stored in order according to a key field To find a particular record All the prior records in the file must be read before the desired record is reached
- 11. Direct File Organization Random file organization Allows direct (random) access The ability to go directly to the desired record by using a record key The benefit the ability to read, change, and return a record to its same place on the disk called updating in place
- 12. Direct File Organization To find the record on a disk Used a certain formula to apply to the record key Deriving a number to use as the disk address Hashing, or randomizing algorithm The mathematical operation that is applied to a key to yield a number that represents the address
- 13. Simple Hashing Schemes A general idea of how the process works
- 15. Hashing Algorithm Collision For a hashing algorithm to produce the same disk address (called synonym) for two different records Even though the record keys are unique To recover from a collision One way : to use the next available record slot in the disk fig 6-13
- 16. Indexed File Organization A compromise between the sequential and direct methods Records are stored in sequential order The file also contains an index The index contain The record key The address associated with the key
- 17. Storage media Tape storage Limited to sequential file organization Disk storage May be sequential , and also accessed directly a direct-access storage device (DASD) The computer can go directly to the desired record on the disk
- 18. How to process the file
- 19. Processing stored data Most business file processing involves processing transactions to update a master file Transaction : a business event that required the business’s records to be updated Ex. a retail sale, the receipt of ordered goods Master file : contains data that must be updated as transactions occur Ex. an inventory file, an employee file, a customer file
- 20. Processing stored data Two main methods Batch processing Transaction processing
- 21. Batch processing A technique of processing transaction data in groups at a more convenient later time Transactions are collected into batches to be processed at a time when the computer may have few online users and thus be more accessible, often during the night No direct user interaction Ex. web page club’s member file
- 22. Batch processing Transaction file Contains all changes to be made to the master file: additions, deletions, and revisions Master file Periodically updated with the changes called for in the transaction file
- 23. Batch processing Changes are stored in transaction files Transaction file is sorted by a key field All the transactions are in sequential order Ex. By the member number of the webpage club Matching the keys from the mater file and transaction files Records of mater file already are in order CPU processes the appropriate action A newly updated master file is created
- 25. Batch processing Advantage Efficiency Disadvantage The master file is current only immediately after processing
- 26. Transaction processing A technique of processing transactions immediately, as they occur Each transaction is handled immediately Real-time processing A transaction is processed fast enough for the result to come back and be acted upon right away Online : the terminals must be connected directly to the computer Ex. bank withdrawal, flight reservation
- 27. Transaction processing Use disk storage For direct access to the desired record Advantage Immediate access to stored data Immediate updating of the stored data
- 29. Batch & Transaction Processing Numerous computer system combine the best features of both methods of processing Transaction processing : used for activities related to the current needs of people Batch processing : done at any time, even in the middle of the night
- 30. Batch & Transaction Processing Ex. Store system Updating the individual item’s inventory Needed transaction processing Producing daily and weekly sales report Used batch processing