Monolith code bases usually use a primary relational database for persistence. Modern web frameworks are often packaged with object-relational mapping (ORM), which allows you to define your domain objects using classes that correspond to tables in the database. Instances of these model classes correspond to rows in the table. As monolith code bases grow, it's not uncommon to see additional data stores, such as document or key value stores, be added.
Microservices should not share access with the same database your monolith connects to. Doing so will inevitably cause problems when trying to coordinate data migrations, such as schema changes. Even schema-less stores will cause problems when you change the way data ...
