# Key Concepts

- [Entity Relationship (ER) Diagram](/data/data-modelling/key-concepts/entity-relationship-er-diagram.md)
- [Conceptual, Logical, and Physical Models](/data/data-modelling/key-concepts/conceptual-logical-and-physical-models.md)
- [OLTP and OLAP](/data/data-modelling/key-concepts/oltp-and-olap.md)
- [Database Optimization](/data/data-modelling/key-concepts/database-optimization.md)
- [DWH design approaches](/data/data-modelling/key-concepts/dwh-design-approaches.md)
- [Dimensional Modeling (DM)](/data/data-modelling/key-concepts/dimensional-modeling-dm.md)
- [Star and Snowflake Schemas](/data/data-modelling/key-concepts/dimensional-modeling-dm/star-and-snowflake-schemas.md)
- [Slowly Changing Dimensions (SCD)](/data/data-modelling/key-concepts/dimensional-modeling-dm/slowly-changing-dimensions-scd.md)
- [Conformed Dimensions](/data/data-modelling/key-concepts/dimensional-modeling-dm/conformed-dimensions.md)