How do I tell lost updates and dirty reads apart in IB Computer Science questions?

Look for whether the problem is about writing or reading. A lost update is fundamentally a write-write conflict where one update overwrites another, so the final value is missing a legitimate change. A dirty read is a read-write conflict where one transaction reads a value that another transaction has changed but not committed. In exam questions, the hint is often the word “rollback” or “not committed yet” for dirty reads. If the scenario ends with “only one change shows up,” that’s usually a lost update. When you answer, explicitly mention timing and visibility of intermediate states, because that is what separates the two.

Why does Isolation matter so much compared to the other ACID properties?

Isolation is the ACID property most directly aimed at concurrency problems. Atomicity ensures a transaction is all-or-nothing, but it doesn’t automatically stop other transactions from seeing intermediate states. Consistency is about rules and validity, but concurrency can still produce valid-looking numbers that are wrong in context. Durability only matters after commit, so it doesn’t prevent interference during execution. Isolation is what keeps overlapping transactions from stepping on each other’s toes. In IB Computer Science, if a question is about lost updates or dirty reads, the most consistent scoring move is to link your explanation back to insufficient isolation.

What should I write for “how to prevent it” without going beyond the syllabus?

Stay high-level and accurate. You can say databases use transaction isolation and concurrency control mechanisms so that transactions do not interfere and uncommitted changes are not visible. Mention locking as a standard approach: a transaction can lock a record/table while updating, preventing other transactions from reading or writing until it commits. You can also mention that the DBMS controls when updates become visible to other transactions. If you want an extra sentence, connect it to ACID: “These mechanisms enforce Isolation so the database remains consistent under concurrent access.” That is usually enough for full credit in IB Computer Science without drifting into unnecessary implementation detail.