Through APIs (request/response) or events (publish/subscribe). A service owns its data and exposes it via stable contracts; other services can build read models or caches from events when they need local reads.
Advanced answer
Deep dive
Expanding on the short answer — what usually matters in practice:
Explain the "why", not just the "what" (intuition + consequences).
Trade-offs: what you gain/lose (time, memory, complexity, risk).
Edge cases: empty inputs, large inputs, invalid inputs, concurrency.
Examples
A tiny example (an explanation template):
// Example: discuss trade-offs for "if-services-can’t-share-a-db,-how-do-they-share-"
function explain() {
// Start from the core idea:
// Through APIs (request/response) or events (publish/subscribe). A service owns its data and
}
Common pitfalls
Too generic: no concrete trade-offs or examples.
Mixing average-case and worst-case (e.g., complexity).