ERD and different data models

General Questions/Discussions
#1

Hi,

I am not completely clear on how to use the different data models of an ERD like it’s shown here: http://www.visual-paradigm.com/highlight/erddatamodel.jsp

My Questions are:

  1. What exactly is the difference if I declare an ERD as a conceptual, logical or physical model? I understand the reason, why you would seperate them and e.g. not show the attributes in the conceptual model. But that is an option of the presentation options in the right-click menu I can select. If I change the data model in the right-click menu, nothing happens. So what is it good for?

  2. If I hide some relationship-lines for better readability, how can I re-show them again? Right-clicking on the entity and selecting “show relationships” doesn’t work.

  3. The just mentioned “show relationships” seems to update the shown relationships if you modified them in your e.g. logical model and want to apply them to your conceptual model. And this leads me to a big question: If you have different data models for ONE thing, then why are new entities you have put in one model not inserted into the other models? Of course, you can copy the new entities to the other models, but it’s very easy to forget an entity. So, why not some “synchronize”-functionality. For that to work, you would have to set a relation between the different data models which reference the same things.

If I am missing some functionality which is already there then excuse me, I am a pretty new user.

Thanks for the great program!
neo

#2

Hi Neo,

Thanks for you post. For your questions:

  1. The 3 types of ER models are separate models which representing different perspectives of your ER model, you will need to model these 3 types of model on your own in order to present your ER model.

  2. If you have hid the relationships (connectors), you need to right-click on the diagram and select Show/Hide > Show > %connectors_you_want_to_show% in the popup menu.

  3. As I mentioned in 1 that conceptual, logical and physical model are separate, they do not have any influence to others, i.e. no “synchronization” function will be available.

FYI, more details about modeling conceptual, logical and physical model can be found at http://resources.visual-paradigm.com/index.php/release-vpsuite-34/58-vpsuite-34/106-erd-data-model.html

If there is any further inquiry, please do not hesitate to ask.

Best regards,
Lilian Wong