SQL Server Performance Forum – Threads Archive

logical model

i have a sql server 2000 database.
this was designed when i took this job over.
there exits no conceptual or logical models. just the database on the sql server. Now someone is asking for a logical model of this database. what should I do here?
thx.

How about a Database Diagram from EM?
Luis Martin
Moderator
SQL-Server-Performance.com All postings are provided â€œAS ISâ€ with no warranties for accuracy.

Give them a blank page. Apparently, that’s how they do logical data modeling there. You could also pull a data model, and give them a table view only (no columns). This might pass if they have no clue what they’re asking for. MeanOldDBA
[email protected] When life gives you a lemon, fire the DBA.

you could also try using an 3rd party app which reverse engineers a model of your database, such as Microsoft Visio, ERWin or Embarcadero ERStudio. although if you just want a diagram EM diagrammer is basically good enough. Tom Pullen
DBA, Oxfam GB

but a logical data model may not have all the tables as a physical model does.
also may not have all the fields, etc.
so if I use a Database Diagram from EM or a reverse engineer via Visio, all these are physical data model.
they need logical.

May not. But all tables with relations is a logical model. Check i.ehttp://dast.nlanr.net/Clearinghouse/DBDesign.html
Luis Martin
Moderator
SQL-Server-Performance.com All postings are provided â€œAS ISâ€ with no warranties for accuracy.

Sybase Power Designer is a good tool as well.

should a logical model have lookup tables? (i assume no)

I assume no too.
Luis Martin
Moderator
SQL-Server-Performance.com All postings are provided â€œAS ISâ€ with no warranties for accuracy.

Sybase Power Designer is horrible. <img src=’/community/emoticons/emotion-1.gif’ alt=’

‘ /> Embarcadero and ERWin are both much better tools. A logical model should represent business process and flow. You can’t create it off the physical model and just drop some information off of it. Just giving someone a bunch of tables with relationships doesn’t mean anything. Having a logical model without verbage means nothing. It might look good on paper. It’s the process of documenting what high level entities are out there, and how they flow through the business and between other entities, that give the logical data model true meaning and significance in the data modeling process. By going through this process, a solid normalized core with identified areas of denormalization can be created that really support the business, while providing long-term stability and usage of the data. Doing it after the fact just to provide a "check off list" is a waste of time and resources. [/rant] MeanOldDBA [email protected] When life gives you a lemon, fire the DBA.

Derrick, I am afraid I don’t agree. I have been using Power Designer for a long time, but now I use Embarcadero (I changed employer). I don’t see advantages you are talking about. Business processes and data flow is another view (I used Power Designer process analyst for that), but logical db model is about entities, relationships and attributes. I’ve found Power Designer an excellent tool with good balance between complexity and ease of use. Just for the record: I found Embarcadero ER/Studio good tool as well, but calling PD horrible comparing to Embarcadero is exaggeration (avoiding stronger words I had in mind). I don’t have (recent) experience with ERWin but it looks like you put it in the same category as Embarcadero. Bfarr23 – I guess everyone is biased about tool he is using the most. I think you can download evaluation copy of any tool mentioned and evaluate it yourself. I guess reverse engineering from physical model is exactly what you need. I know both Power Designer and Embarcadero can do that and I am quite sure ERWin can do it too.

Power Designer doesn’t do it correctly. I’m biased against Power Designer because after using ERWin I found it extremely difficult to use and very lacking in functionality that should be right after all these years. The logical data model is all about entities and relationships. It’s built around: 1. A base exploration of the entities, which will include some high level attributes needed to describe the entity. 2. A modeling of the data processes through good business process analysis. So, we’ll agree to disagree on this one. <img src=’/community/emoticons/emotion-1.gif’ alt=’

‘ /> The logical model doesn’t do you any good if you don’t go through this process. MeanOldDBA [email protected] When life gives you a lemon, fire the DBA.

on the Lookup thing. I consider a Lookup table as a table with a near static list of items. ex. Credit card types. We also have a table here like Group.
ex. Group
GroupID (PK) Individual
IndividualID (PK) Individual_Group
GroupID(PK, FK)
IndividualID (PK, FK)
Would you guys consider Group as a Lookup table also? – Group would have a near static list of items. what u think?

<blockquote id="quote">quote:<hr height="1" noshade id="quote"> Power Designer doesn’t do it correctly.<hr height="1" noshade id="quote"></blockquote id="quote"> Are you against reverse engineering from physical model? <blockquote id="quote">quote:<hr height="1" noshade id="quote">I’m biased against Power Designer because after using ERWin I found it extremely difficult to use and very lacking in functionality that should be right after all these years.<hr height="1" noshade id="quote"></blockquote id="quote">This is for the first time I’ve heard someone finding PD difficult to use. About functionality I’m sure you can make a point about features you are missing and I can’t really argue. I used Process Analyst for data flow diagrams but this product is replaced by business process analyst I didn’t have opportunity to use (because I moved to new company).<blockquote id="quote">quote:<hr height="1" noshade id="quote">The logical model doesn’t do you any good if you don’t go through this process.<hr height="1" noshade id="quote"></blockquote id="quote">Except when you are requested to produce it on already deployed app ASAP and then to continue work on figuring out how data actually flow through the system. <blockquote id="quote">quote:<hr height="1" noshade id="quote">So, we’ll agree to disagree on this one. <img src=’/community/emoticons/emotion-1.gif’ alt=’

‘ /><hr height="1" noshade id="quote"></blockquote id="quote">Ok, I don’t have PD installed to be able to go through it and discuss and I don’t have time for it. Maybe one day if I am assigned to select the tool from the market I’ll come back to you to learn about your experience with either tool.

quote:
Except when you are requested to produce it on already deployed app ASAP and then to continue work on figuring out how data actually flow through the system.

Agreed. I would try to educate whoever is requesting it though on why just handing them a logical model produced this way would be, for the most part, a waste of time, and why they should go through the process of creating a real logical data model even if it’s a reversal of the normal path to get one. If they don’t agree, then give them something to make them happy. Having something just to say "look what I have" is a waste of time and resources. Unfortunately, sometimes that’s what we’re stuck with.

quote:
Are you against reverse engineering from physical model?

No. ???????? The ability to correctly reverse engineer and diff is critical to me using any kind of modeling tool. In this facet (especially diffs), Embarcadero is a better tool. MeanOldDBA
[email protected] When life gives you a lemon, fire the DBA.

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