Can I have a table in my ER diagram which is not connected and does not have any relationships with the other tables?
Related
If I have an ER Diagram as such:
ER Diagram
How would I express this in a relational schema?
I have a question regarding ER diagram
The question is how do we connect entities in an ER diagram
the options are
1. foreign key
2. relationship
3. primarykey
4. association
I know if the question was about relational diagram the answer will be: FK, but as I recall there is no FK in ER diagram and the book says the right answer is 1, so any help?
I'm using StarUML in order to do a ER diagram and I can create relation with two entities like this:
and in StarUML:
But I cannot create a relation with 3 entity like this:
Have you some ideas to do it in StarUML?
It looks like the StarUML supports only the physical ER diagram symbols and you need to represent your database structure using a physical ER translation.
you can also find some reference here
https://www.lucidchart.com/pages/ER-diagram-symbols-and-meaning
1.Several students from different departments may participate one project. Each project has at least one student member.
2.Each student may or may not participate the projects, but one student can participate several projects at the same time.
In 1st statement, the relationship of student and project is M-1. But in the 2nd statement, the relationship of student and project is 1-M
If I want to express their relationship in a single ER digram, should I use the M-1 or 1-M? Or is my ER diagram wrong?
ER Relation
In some ER diagrams there are attributes on the relation.In what occasions should we use attributes on the relation
Attributes on relationships allow you to record facts about the relationship as opposed to one of the entities that make up the relationship. Some examples:
A marriage between two people has a date and venue
A student's class allocation may have an assigned seat
Popularity ratings by customers on products
Here's an ER example of an attribute on a relationship between student and class:
While the semantics of ER seem familiar and aid its popularity, logically the distinction between entities and relationships is artificial and unnecessary. Entities can have composite keys, and unary relations aren't unusual from an n-ary relational point of view.