tag:blogger.com,1999:blog-6393051114813114443.post2782628143145251096..comments2024-03-27T14:52:51.318-05:00Comments on Lee's Blog: The Importance of a Logical Data ModelLee Richardsonhttp://www.blogger.com/profile/01314803491511307042noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-6393051114813114443.post-80817394077065582582008-02-28T11:34:00.000-05:002008-02-28T11:34:00.000-05:00"The only reason I can see is to simplify for non-..."The only reason I can see is to simplify for non-tech people"<BR/><BR/>I don't buy that argument, but there are some similar ones. For instance sometimes it is politically advantageous to present things one way when you actually implement them another.<BR/><BR/>But after reading your comment and re-reading my post about a year later I think the visual example is too convoluted. But that doesn't mean I still don't believe in the value of logical models to display the way things really are vs the way the database portrays them.<BR/><BR/>For instance I have occasionally found it useful to denormalize my physical more than my logical for either performance reasons, or because too many 1-1 relationships can just get cumbersome in code, even with a good ORM tool. I talk about this somewhat in my <A HREF="http://rapidapplicationdevelopment.blogspot.com/2007/07/referential-integrity-data-modeling.html" REL="nofollow">Data Modeling Mistakes</A> series.Lee Richardsonhttps://www.blogger.com/profile/01314803491511307042noreply@blogger.comtag:blogger.com,1999:blog-6393051114813114443.post-17068649572974636772008-02-26T17:22:00.000-05:002008-02-26T17:22:00.000-05:00Well, I don't really see the advantage of your vis...Well, I don't really see the advantage of your visual example. I am looking for reasons to embrace the Logical Data Model and that is how I stumbled across your page.<BR/><BR/>As far as I can tell, the only reason you would separate out employee from company in the way shown is if and employee could have multiple companies at different points in time AND you cared about the previous companies. This can be known up front and usually is and could be designed for immediately. So why initially denormalize them? The only reason I can see is to simplify for non-tech people. I have to search for more justifications for Logical Data Model.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-6393051114813114443.post-46573422730622761242007-06-22T14:47:00.000-05:002007-06-22T14:47:00.000-05:00Sai,I would say the difference between a logical a...Sai,<BR/><BR/>I would say the difference between a logical and physical data model is an area up for debate. In terms of things people can probably universally agree upon:<BR/><BR/>1. Logical data models have many-to-many relationships where physical data models have associative or resolution tables.<BR/><BR/>2. The goal of a logical data model is primarily to identify entities and their relationships while ignoring the details of primary keys, foreign keys, and indexes, while the goal of the physical data model is to hold data, access it quickly etc.<BR/><BR/>Microsoft Visio, my preferred modeling tool, doesn't support #1, so that's a moot point for me. And as far as #2, on my projects I gradually refine the logical data model into a physical one, so the goals overlap.<BR/><BR/>So in my world the two would always be nearly identical except when politics or performance dictate the need to denormalize (i.e. my logical model is almost always more normalized than my physical model).<BR/><BR/>You're the second person now to point out my somewhat casual use of the terms, so I've listed it in my ideas for future blog entries.Lee Richardsonhttps://www.blogger.com/profile/01314803491511307042noreply@blogger.comtag:blogger.com,1999:blog-6393051114813114443.post-58243534972961433622007-06-22T14:21:00.000-05:002007-06-22T14:21:00.000-05:00Hi. I was looking at your physical and logical mod...Hi. I was looking at your physical and logical model and it seems that the logical model looks like a physical model.<BR/><BR/>From what I have done, in a logical mode, I would use more of business terms. <BR/><BR/>I could be wrong though... Would like your thouhts pleaseSainathKhttps://www.blogger.com/profile/11948482000903911563noreply@blogger.com