# Problem Typology: Rating Prediction vs. Ranking vs. Top-N Retrieval vs. Sequential

> Source: https://sukruyusufkaya.com/en/learn/oneri-sistemleri/problem-tipolojisi-rating-ranking-topn-sequential
> Updated: 2026-05-13T13:29:33.531Z
> Category: Öneri Sistemleri
> Module: Module 1: Landscape of Recommender Systems & Problem Formulation
**TLDR:** A recommender problem can be formulated in 4 different ways — and choosing the right formulation is often more important than choosing the right algorithm. Each one's mathematical definition, when to choose, which metric, and which real scenarios.