Database Design – Understanding Entity-Relationship Diagram (ERD) Symbols in DBeaver

ISA in First diagram has no point. ISA is used as "either".

Movie CAN BE a Cartoon or Natural or movie MUST BE a cartoon or Natural.

There is no point to append an ISA while there is no either condition

I am not sure if this is the right place to pose such questions. But here some remarks and questions anyway. They are too long for a comment.

• I don't understand the word representant. I did not find it at http://dict.leo.org/. Dou you mean representative?

• With telephones you mean phone numbers and with emails you mean email adresses?

• Why is telephone a weak entity? What is its identifying entity? For me it is not a weak entity. A phone extension may be a weak entity. The same holds for email and address.

• can a representant have more then one address? This is not excluded by the text but it is excluded by the ER diagtram.

• Why do you name some entities as singular and some as plural? I think a consisten notation will be more clear.

• Why do one need a reading direction? What is the difference if one reads the diagram from bottom to top? I see no difference.

• "if a representant is removed it must be saved in a list" That does not describe any relationships between a removed representant and the remaining entities. "it must be saved" is a term of computer programming and not of the business domain. It is not clear to me what you want but using an attribute to a relation may be not the appropriate solution. From your drawing I conclude a telephone is assigned to a representant. If the representant is removed the removed representant has a telephone too? If yes then this telephone cannot be used by then new representant for this address because a telephone has only one representant assigned.