問79
頻出度★☆☆
ファイルのあるレコードが変更されたときに, 変更された内容を特定する方法として, 適切なものはどれか。
平成27年度 秋期 ITパスポート試験 問79
テクノロジ系ソフトウェア › ファイルシステム
This question's explanation and your answers so far.
解説
問 79
Incorrectア
If you record the file's size and update date/time, you can detect the fact that a change occurred when a value changes, but you cannot know the content, that is, which part of which record changed and how. If an overwrite leaves the size unchanged, the change may even be missed.
- イ
正解 To identify what content was changed, you must keep the state of the file (record) before the change at hand and compare it against the state after the change. Choice イ keeps a copy (backup) in advance and later compares it with the current file, so it can specifically reveal which item of which record was rewritten and how. Holding a baseline for taking the difference (a snapshot from before the change) is the key to identifying the content, and choice イ satisfies this.
Incorrectウ
Even if you record the number of records, you can only detect additions or deletions that change the count; when the contents of an existing record are rewritten the count does not change, so it is of no help in identifying what was changed.
Incorrectエ
Sorting the records into ascending order by key item is a technique for making search or ordering more efficient; it does not hold any material for comparing before and after the change (the old data that serves as a baseline), so it cannot be a means of identifying what content was changed.
ここがポイント
- To identify the changed content, the basic approach is to keep a snapshot from before the change (a copy or backup) and compare the difference against the state after the change.
- Size, update date/time, and record count can be used to detect whether a change occurred, but cannot reveal the content of what changed and how.
用語