# Miscellaneous > Database Design >  for experts about operations to data access in ER diagram

## zio_mangrovia

If I have ER schema where I have: 

2 entity: Room, Hotel 
1 relationship: Link 
Cardinality about Room side is (1:1) each room belongs only to one hotel 
Cardinality about Hotel side (1:N) each hotel can have more than one 
Hotel has code attribute as primary key. 
Room has foreign key: room number attribute + hotel code. 

see: https://ibb.co/f471m9Q

My doubt is about operation to evaluate performance database before to migrate to logical model, infact this step is necessary during ER restructuring. 
My question: 

I have hotel code (e.g. hotel Europe) and I need to know what rooms numbers are in that hotel, I have to access only to relationship "link" or I need to access to Room entity too? 
I'd like to understand if, at level ER diagram, "link" relationship contains number attribute too. Thanks

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## skhanal

Is Room Number an attribute of Room entity?

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## zio_mangrovia

> Is Room Number an attribute of Room entity?


Yes, It is.

ers.PNG

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## skhanal

In ER diagram, link does not tell you about attributes, so you have to read Room entity for Room number. When you convert this to physical model, there is no physical representation for 1-1 and 1-m relations.

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