In this session, we will review the origins, history, and architecture of the Common Data Service. We will see how some of the inheritance of their SQL 2000 based ancestors still show up today, and how they impact us. We will also discuss some of the complexities of the data modelling on the CDS, and what is the impact of all those options we have when creating new entities. We will review How and When to use some of the different particular data types and their limitations. Finally, we will discuss some of the crucial design decisions when building your data model.