Solved

Weak and Strong Entities

Posted on 1998-11-27
5
8,394 Views
Last Modified: 2006-11-17
Description of Weak and Strong Entities.
0
Comment
Question by:majorjohn
5 Comments
 
LVL 2

Expert Comment

by:pjmaze
ID: 1026018
hi,

The existance of a weak entity depends on the existence of a strong entity; it must relate to the strong via a on-to-many relationship set.

The primary key of a weak entity is formed by the primary key of the strong entity on which the weak entity set is existence depend, plus the weak entity set’s discriminator (partial Key).



A strong entity is one that has its own primary key and dont depand on any other entitie.

If you need more info, ask ..

see ya
0
 
LVL 1

Author Comment

by:majorjohn
ID: 1026019
Yes I need some more information with example.

Thanks,
0
 

Expert Comment

by:camazorro
ID: 1026020
Hi MajorJohn

Typical Expample of weak and strong entity

EMPLOYEE and DEPENDANTS

The entity DEPENDANTS depends of the entity EMPLOYEE
DEPENDANTS = Wife, childrens, family.

In a Company DB the DEPENDANTS entity can exist by it self. In these case we make the relation DEPENDANTS --<depends>-- EMPLOYEE

Bye Bye
0
 
LVL 3

Expert Comment

by:P_S_Price
ID: 1026021
The above model may not be a true example. It could also be possible for a dependent to be an Employee!! Nepotism is best kept in the family!!
0
 
LVL 3

Accepted Solution

by:
traygreen earned 10 total points
ID: 1026022
Strong entity...
Table Orders
ID        int      Primary Key
OrderNum  varchar
OrderDate datetime

Table Items
ID        int      Primary Key
Desc      varchar

weak....
Table OrderDetail
OrderID   int      Foreign Key (references Order.ID)
ItemID    int      Foreign Key (references Item.ID)
Qty       int

In this example the items and orders tables are core level or "Stong" entities.  They stand alone without requiring other defined objects.
The Order detail is a "Weak" entity as it requires the existence of both an order and item to exist.

Is this what you are looking for?
0

Featured Post

What is SQL Server and how does it work?

The purpose of this paper is to provide you background on SQL Server. It’s your self-study guide for learning fundamentals. It includes both the history of SQL and its technical basics. Concepts and definitions will form the solid foundation of your future DBA expertise.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
export Oracle diagram from Oracle DB including VIEWS 8 128
SQL Database connect change in Access 2015 5 58
Trouble connecting to SqlServer database 4 60
SQL Query 34 99
I annotated my article on ransomware somewhat extensively, but I keep adding new references and wanted to put a link to the reference library.  Despite all the reference tools I have on hand, it was not easy to find a way to do this easily. I finall…
CCModeler offers a way to enter basic information like entities, attributes and relationships and export them as yEd or erviz diagram. It also can import existing Access or SQL Server tables with relationships.
Video by: Steve
Using examples as well as descriptions, step through each of the common simple join types, explaining differences in syntax, differences in expected outputs and showing how the queries run along with the actual outputs based upon a simple set of dem…
Polish reports in Access so they look terrific. Take yourself to another level. Equations, Back Color, Alternate Back Color. Write easy VBA Code. Tighten space to use less pages. Launch report from a menu, considering criteria only when it is filled…

770 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question