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Should module be decoupled from each other to the extent that they can possibly have their own database? Implications: no foreign key relationship, possible independent hosting and deployment.
Which layers in a module are accessible to another module at the compile time?
Entities in one module would refer to entities in another module. In such a case should there be hibernate based relationship between entities?
Which module hosts the page which displays data from two functional modules?
In case of 1One-to-1One/1One-to-Many/Many-to-1 One (logical) relationships between entities how to decide who refers to whom? How to avoid cyclic relationships between modules?
If there is a no domain relationship
Notify of event than tell what to do.
Should domain layer know about the its own service layer or other service layersbetween entities in different modules. A parent entity (in module A) has child entity (in module B), when the child entity is created, how does parent entity get the id for it?
Guidelines
A functional module's service/domain-layer wants to read the data owned by another functional module.