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Results tagged with erd
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user 993
Entity Relationship Diagram
1
vote
Modeling a database for a printing company
This part in Item doesn't look right:
F.K = JID, OID
JID REFERENCES PURCHASE (JID)
OID REFERENCES PURCHASE (OID)
I suppose the design is only on paper, as no DBMS would allow that, when the pri …
- 98.6k
20
votes
Accepted
Implementation of a many-to-many relationship with total participation constraints in SQL
It's not easy to do in SQL but it is not impossible. If you want this enforced through DDL alone, the DBMS has to have implemented DEFERRABLE constraints. This could be done (and can be checked to wor …
- 98.6k
4
votes
how do I model this in database?
City
----
CityID
CityName
PRIMARY KEY (CityID)
Hotel
-----
HotelID
HotelName
CityID
PRIMARY KEY (HotelID)
FOREIGN KEY (CityID)
REFERENCES City (CityID)
Package
-------
PackageID
PackageName
CityID …
- 98.6k
2
votes
Accepted
EER Diagram - subclasses which are neither disjoint nor fully overlapping
Assumptions:
A service can be of either type A or B. Not both.
A request can be for either a service of type A or for two services (one of type A and one of type B).
A client can have many requests. …
- 98.6k
3
votes
Accepted
What is the cardinality of entity relationship between Employee and Department?
What is the cardinality of (this) entity relationship between Employee and Department?
Yes, this relationship ("managed-by") is an example of a one-to-one relationship. This doesn't forbid the tw …
- 98.6k
1
vote
Accepted
Ternary Relationship or (n-ary)
Yes, there is a difference.
In the 1st design, an author-paper combination is related to one editor. So a paper can have many editors, as many as its authors.
In the 2nd design, a paper is related t …
- 98.6k
6
votes
Accepted
Modeling Subclass (or Subtype) Constraints in an Entity-Relationship Diagram
I think you can make an Orders entity that is a relationship between Products and Customers. The Orders would have subclasses FoodOrders and ShoeOrders, which respectively would be the relationships b …
- 98.6k