Various systems and methods can provide a flexible database schema. One method can store information identifying a first entity in a first table. A unified data model includes several tables, including the first table and a metadata table. Each of the tables stores information describing one or more entities belonging to a respective archetype. The first table already stores information identifying a second entity when the information identifying the first entity is stored. The second entity is already related to another entity when the information identifying the first entity is stored. The first entity is a new type of entity not already stored in the first table when the information identifying the first entity is stored. The method then stores metadata associated with the first entity in a metadata table. The metadata then identifies the new type of entity.