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Results tagged with erd
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user 70203
Entity Relationship Diagram
5
votes
Accepted
Entity set that has a relationship with itself
There's nothing in the ERD to constrain the model either way. … For example, assuming the ERD is implemented as:
Person (personId PK, dateOfBirth, name, gender)
ChildOf (personId PK/FK, parentId FK)
we could record the following sets of rows:
Person (1, 2000-11 …
- 393
3
votes
ERD for a web development company
You're oversimplifying the relations. No two relations in your diagram are the same, since they don't relate the same domains. <ORDER> has <ORDER-ITEM> is not the same as <PROJECT> has <PROJECT-PHAS …
- 393
3
votes
What's the point of the relationship diamond in Entity-Relationship diagrams?
Peter Chen, who invented the ER model and the notation containing diamonds for relationships, distinguished two kinds of relations - entity relations and relationship relations. Each were intended to …
- 393
2
votes
Accepted
Is it possible to represent a ‘mutual IS-A’ relationship in an entity-relationship diagram?
In databases, subtyping means that one domain is a subset of another. If A is a subset of B and B is a subset of A, then it means A = B. The same logic applies whether A and B are entity sets or relat …
- 393
2
votes
Accepted
How many tables are needed to implement the scenario depicted in my entity-relationship diag...
Your answer is mostly correct, except Q is a dependent attribute of R3, not a table on its own.
- 393
2
votes
Can an entity in an entity-relationship diagram have more than one relationship?
It means that time is an essential component of the relationship. It's telling you that there's a functional dependency (employee, time) -> project.
In an entity-relationship diagram, I might model …
- 393