I am working with an ERD. It is supposedly a logical model and I am to make a physical model from it. I should be formatting in UML and our DBMS is PostgreSQL.
Some of my research (http://www.1keydata.com/datawarehousing/data-modeling-levels.html // http://en.wikipedia.org/wiki/Logical_data_model#Conceptual.2C_Logical_.26_Physical_Data_Model) indicates that this ERD may have too much information in it to be a logical model and that it may actually be closer to the physical.
My questions are as follows:
- What do the bold labels mean?
- What do the white "N"s and red "U"s at the end of some entries mean?
- What is the difference between a dashed line (relationship) and a solid one?
- What is the difference between the "crows foot" and the broken line on either end of the relationship?
- Is this closer to the physical model or logical model? What would I have to do to convert it from one to the other?
This is the ERD:
Logical/physical models in the information modelling sense should not be confused with what are termed the logical level and physical level in DBMS architecture and database theory. In principle relational database tables (AKA relation variables) are always "logical" level constructs but in data modelling terms they are part of a so-called "physical" model. That unfortunate choice of modelling terminology is responsible for a lot of confusion and misunderstandings.