Entity Relationship Diagramming

Posted by Ben Aston on Stack Overflow See other posts from Stack Overflow or by Ben Aston
Published on 2010-04-19T08:57:40Z Indexed on 2010/04/19 11:23 UTC
Read the original article Hit count: 499

Filed under:

data-modelling

|

er-diagrams

I'd like to improve my understanding of cardinality constraints in ER diagrams.

I have two entities:

User
Location

But, I want the relationship between these two entities to be many-to-many (a user can be in many locations and a location can have many users).

To do this I need to introduce an association class UserLocation.

Is it correct to say I now have 3 entities?

If I were to draw an ER diagam of the above, would I draw in the UserLocation entity, and would the cardinality look like this?

User 1 ------ * User Location *  ------ 1 Location

© Stack Overflow or respective owner

Related posts about data-modelling

Collaborative data modelling software?

as seen on Super User - Search for 'Super User'
I'm trying to find a tool where a lot of people can work on a data model collaboratively. Embarcadero has a an ER application called ER/studio which apparently comes with a repository system that acts like typical version control software. That sounds great except ER/studio is expensive and this… >>> More
Webbased data modelling and management tool

as seen on Stack Overflow - Search for 'Stack Overflow'
Is there a web-based tool available, where I am able to... ...define data models (like in a database admin tool) ...fill in data (in custom web forms, not too generic) with basic features like completion ...import data from CSV oder Excel Sheets ...export data to CSV or SQL ...create snapshots… >>> More
Twitter status id conundrum

as seen on SQL Blog - Search for 'SQL Blog'
I have an interest, a slightly perverse one some might say, in using online services and trying to figure out what the underlying (logical) data model is and in this day and age Twitter is one that lends itself very well to scrutiny. Consider this recent tweet of mine: The URL that enables… >>> More
How to show or direct a business analyst to a data modelling subject?

as seen on Programmers - Search for 'Programmers'
Our business analysts pushed hard to collect data through a spreadsheet. I am the programmer responsible for importing that data. Usually when they push hard for something like this, I never know how well it will work out until a few weeks later when I have time assigned to work on the task of programming… >>> More
How to show or direct a business analyst to do data modelling?

as seen on Programmers - Search for 'Programmers'
Our business analysts pushed hard to collect data through a spreadsheet. I am the programmer responsible for importing that data. Usually when they push hard for something like this, I never know how well it will work out until a few weeks later when I have time assigned to work on the task of programming… >>> More

Related posts about er-diagrams

Types of ER Diagrams

as seen on Programmers - Search for 'Programmers'
I'm currently taking a class for database design, and we're using the ER diagram style designed by Peter Chen. I have a couple of problems with this style: Keys in relationships don't seem realistic. In practice, synthetic keys like "orderid" seem to be used in almost all tables, including association… >>> More
Tables as relations in ER diagrams

as seen on Stack Overflow - Search for 'Stack Overflow'
Assume I have the following tables (**bold** - primary key, *italics* - foreign key): patient(**patient_id**, name) disease(**disease_id**, name) patient_disease(**p_d_id**, *patient_id*, *disease,_id* ) I want to draw the ER diagram for this. My idea is to make two entities, one for patient and… >>> More
Entity Relationship Diagramming

as seen on Stack Overflow - Search for 'Stack Overflow'
I'd like to improve my understanding of cardinality constraints in ER diagrams. I have two entities: User Location But, I want the relationship between these two entities to be many-to-many (a user can be in many locations and a location can have many users). To do this I need to introduce an… >>> More
Open source software which allows user to draw ER/flow diagrams for my web application

as seen on Stack Overflow - Search for 'Stack Overflow'
we are developing a web application which allows a user to draw diagrams(flow/ER diagrams) and we need the representation of that diagram in some XML or other formats. How should we acheive this ?? is there any open source software or jQuery plugin or anyother server side software?? >>> More
Conventions for modelling c programs.

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm working with a source base written almost entirely in straight-c (nginx). It does, however, make use of rich high level programming techniques such as compile-time metaprogramming, and OOP - including run-time dispatch. I want to draw ER diagrams, UML class diagrams and UML sequence diagrams… >>> More