Accounts payable design: when should the pending invoice file be kept on a direct-access storage device (DASD)?

Introduction / Context:
File organization choices affect performance, cost, and responsiveness. Direct-access storage (DASD)—such as disks—supports rapid random retrieval, which is vital for interactive query workloads. In accounts payable, a “pending invoice” file often requires frequent lookups by vendor, invoice number, or due date, especially when service desks handle queries in real time.

Given Data / Assumptions:

• DASD enables fast random access for online transactions.
• Batch payment execution does not require constant online retrieval.
• “One-line” data entry is incidental to storage access patterns.

Concept / Approach:
Use direct access when the workload is query-intensive and timing-sensitive. For interactive, on-screen inquiries (balance checks, status, exceptions), operators must access specific records quickly. Conversely, batch payment runs can stream sequentially from efficient batch files without demanding random access, and the brevity of data entry lines does not mandate DASD by itself.

Step-by-Step Solution:

Verification / Alternative check:
Classical file-organization guidance aligns indexed/hashed direct access with interactive inquiries and sequential files with batch runs, confirming the choice.

Why Other Options Are Wrong:

• Batch payment execution: sequential runs can read from batch-optimized storage.
• One-line data entry: line length is unrelated to storage access pattern.
• All/None: overinclusive or contradictory.

Common Pitfalls:
Assuming “batch” implies DASD necessity; in fact, batch favors sequential processing, not random access.

Final Answer:
inquiries concerning payables must be answered online