I am designing a new system which is more of a help system for core applications in banks or healthcare sector. Given the nature of the system this is not a heavy transaction oriented system but more of read intensive.

Now within this application I have multiple entities which are related to each other. For e.g. Assume the following entities in the system

1. User
2. Training
3. Regulations

Now each of these entities have M:N Relationship with each other.

Assuming the usage of a standard RDBMS, the design may involve many relationship tables each containing the relationships one other entity ("User_Training", "User_Regulations", "Training_Regulations"). This design is limiting since I have more than 3 entities in the system and maintaining the relationship graph is difficult this way.

The most frequently used operation is "given an entity get me all the related entities" . I need to design the database where this operation is relatively inexpensive.

What are the different recommendations for modelling this kind of database.