In this paper, we introduce MM-cat, a modular and extensible framework that enables to perform all the necessary steps to design a multi-model schema. An initial ER schema is transformed to a unified categorical representation which can then be easily mapped to any combination of models in a particular DBMS, or their set.
In addition, MM-cat also provides a categorical representation of multi-model data instances to be processed uniformly. Both the schema and instance categories serve as the core for further management of multi-model data.
The whole process of transformation to/from the categorical representation is demonstrated using MongoDB and PostgreSQL.