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databaseentity-relationshiperd

Minimum Cardinality in ER diagram

enter image description here

I want to know if this depiction is right or not, If so why there is a partial constraint over the department entity and not the employee.

because the way I depict it is that the employee may or may not participate in managing the department so the employee should have the partial sign and the department must be managed by at most one employee so it should be mandatory over the department entity

Solution

  • Your diagram mixes Chen's notation (the diamond for the relationship) with Crow's foot notation (the graphical cardinality on the lines). This is confusing.

    Either go for Crow's foot notation, just removing the diamond. This is intuitive as the || mean 1..1 and o| mean 0..1 and both follow the same logic regarding the side on which it is shown:

    enter image description here

    Or, go for the correct representation in Chen's notation, using a double line for total participation. This is less intuitive in view of the side where the the total participation is shown:

    enter image description here