ch08 - Chapter 8: CAATTs for Data Extraction and Analysis...

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IT Auditing & Assurance, 2e, Hall & Chapter 8: CAATTs for Data Extraction and Analysis IT Auditing & Assurance, 2e, Hall & Singleton
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DATA STRUCTURES Organization Access method
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SEQUENTIAL ISAM RANDOM INDEX File DATA File SEQUENTIAL RANDOM Data Organization Hashing Pointers Access: Index Methods Access: Non-Index Methods
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FILE PROCESSING OPERATIONS 1. Retrieve a record by key 2. Insert a record 3. Update a record 4. Read a file 5. Find next record 6. Scan a file 7. Delete a record Individual Records Table 8-1
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DATA STRUCTURES Flat file structures Sequential structure [Figure 8-1] All records in contiguous storage spaces in specified sequence (key field) Application reads from beginning in sequence If only small portion of file being processed, inefficient method Does not permit accessing a record directly Efficient: 4, 5 – sometimes 3 Inefficient: 1, 2, 6, 7 – usually 3
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DATA STRUCTURES Flat file structures Indexed structure In addition to data file, separate index file Contains physical address in data file of each indexed record
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DATA STRUCTURES Flat file structures Indexed random file [Figure 8-2] Records are created without regard to physical proximity to other related records Physical organization of index file itself may be sequential or random Random indexes are easier to maintain, sequential more difficult Advantage over sequential: rapid searches Other advantages: processing individual records, efficient usage of disk storage Efficient: 1, 2, 3, 7 Inefficient: 4
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DATA STRUCTURES Flat file structures Indexed Sequential Access Method (ISAM) [Figure 8-3] Large files, routine batch processing Moderate degree of individual record processing Used for files across cylinders Uses number of indexes, with summarized content Access time for single record is slower than Indexed Sequential or Indexed Random Disadvantage: does not perform record insertions efficiently – requires physical relocation of all records beyond that point – SOS Has 3 physical components: indexes, prime data storage area, overflow area [Figure 8-4] Might have to search index, prime data area, and overflow
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ch08 - Chapter 8: CAATTs for Data Extraction and Analysis...

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