[Webinar] Streamline your web hosting managementRegister Today

x
?
Solved

Weak and Strong Entities

Posted on 1998-11-27
5
Medium Priority
?
8,521 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 30 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

The new generation of project management tools

With monday.com’s project management tool, you can see what everyone on your team is working in a single glance. Its intuitive dashboards are customizable, so you can create systems that work for you.

Question has a verified solution.

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

This article shows how to get a list of available printers for display in a drop-down list, and then to use the selected printer to print an Access report or a Word document filled with Access data, using different syntax as needed for working with …
Microsoft Jet database engine errors can crop up out of nowhere to disrupt the working of the Exchange server. Decoding why a particular error occurs goes a long way in determining the right solution for it.
In this video, Percona Solution Engineer Dimitri Vanoverbeke discusses why you want to use at least three nodes in a database cluster. To discuss how Percona Consulting can help with your design and architecture needs for your database and infras…
Hi, this video explains a free download that you can incorporate into your Access databases, or use stand-alone for contact management. Contacts -- Names, Addresses, Phone Numbers, eMail Addresses, Websites, Lists, Projects, Notes, Attachments…
Suggested Courses

612 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