If I have an ER Diagram as such:
ER Diagram
How would I express this in a relational schema?
Related
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
Can I have a table in my ER diagram which is not connected and does not have any relationships with the other tables?
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.
all the attributes include in ER diagram or not?
My database have 8 tables and nearly 50 attributes, i include these 50 attributes in a single diagram OR not?
First thing - ER diagram is something that is first created usually and then later on converted into a data model like relational. So the data storing requirements are modeled into an ER diagram first and later on are converted into tables. There is rarely a case where you have to reverse engineer an existing data model into the ER diagram level (Conceptual Level).
During this process, tables are created for enitities and relationships accordingly (using some algorithmic process).
And a good way of practice is to draw the ER diagram with only entities and relationships without the attributes as it makes it very clumsy and difficult to concentrate on the actual entities and the relationships between them. Later on in a separate document or a page, you can list all the attributes corresponding to entities individually.
Hope this gives you a basic idea.