File storage choice for payables: when should the outstanding (open) invoice file be stored on a direct access storage device (DASD)?

Difficulty: Easy

Correct Answer: when inquiries about accounts payable must be answered online

Explanation:


Introduction / Context:
Choosing the right storage organization for files in an accounting system affects responsiveness and cost. Direct access storage devices (DASD)—a term historically referring to disks—support rapid random access to individual records. Outstanding (open) invoices are frequently queried by vendors, approvers, and finance staff, so access characteristics matter for service levels and productivity.


Given Data / Assumptions:

  • Online inquiries require quick retrieval of specific invoices by key (vendor, invoice number, date).
  • Batch payment runs can tolerate sequential processing.
  • Invoice entry may be online, but inquiry responsiveness is the key driver for random access.


Concept / Approach:
Use DASD when workloads emphasize direct, keyed retrieval. Online inquiry screens call up a small set of invoices out of a large file, which is best served by random access structures (e.g., indexed files, database tables on disk/SSD). Batch payment processing often processes a scheduled set sequentially, which could run efficiently even on sequential storage. A design requirement like “last record points to first” indicates a circular list and is not a valid criterion for choosing DASD by itself.


Step-by-Step Solution:

Identify the scenario that demands random access: online inquiries. Recognize that batch payment recording is typically sequential. Note that online data entry alone does not imply frequent random retrieval by key. Select the option explicitly about online inquiries for payables.


Verification / Alternative check:
File organization principles and DBMS indexing guidelines recommend random-access storage for high-selectivity, user-driven queries, confirming this choice.


Why Other Options Are Wrong:

  • Online entry: focuses on writing records; does not guarantee heavy random lookup needs.
  • Batch payments: suited to sequential processing, not a DASD requirement.
  • Last-to-first pointer: a structural artifact, not a performance/use-case criterion.
  • None: incorrect because one clear case (online inquiries) warrants DASD.


Common Pitfalls:
Assuming online write implies online read patterns; design storage for the dominant access pattern, which for open invoices is often inquiry-heavy.


Final Answer:
when inquiries about accounts payable must be answered online

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