title: Data Modeling: Logical Modeling Exercise
body: <p>In trying to learn the art of data storage I have been trying to take in as much solid information as possible.  PerformanceDBA posted some really helpful tutorials/examples in the following posts among others: <a href="https://stackoverflow.com/questions/4061826/is-my-data-normalized/">is my data normalized?</a> and <a href="https://stackoverflow.com/questions/4702728/relational-table-naming-convention/">Relational table naming convention</a>.  I already asked a subset question of this model <a href="https://stackoverflow.com/questions/4763141/data-modeling-supertype-subtype/">here</a>.</p>
  
  <p>So to make sure I understood the concepts he presented and I have seen elsewhere I wanted to take things a step or two further and see if I am grasping the concepts.  Hence the purpose of this post, which hopefully others can also learn from.  Everything I present is conceptual to me and for learning rather than applying it in some production system.  It would be cool to get some input from PerformanceDBA also since I used his models to get started, but I appreciate all input given from anyone.</p>
  
  <p>As I am new to databases and especially modeling I will be the first to admit that I may not always ask the right questions, explain my thoughts clearly, or use the right verbage due to lack of expertise on the subject.  So please keep that in mind and feel free to steer me in the right direction if I head off track.  </p>
  
  <p>If there is enough interest in this I would like to take this from the logical to physical phases to show the evolution of the process and share it here on Stack.  I will keep this thread for the Logical Diagram though and start new one for the additional steps.  For my understanding I will be building a MySQL DB in the end to run some tests and see if what I came up with actually works.</p>
  
  <p>Here is the list of things that I want to capture in this conceptual model. <strong>Edit for V1.2</strong></p>
  
  <ol>
  <li>The purpose of this is to list Bands, their members, and the Events that they will be appearing at, as well as offer music and other merchandise for sale</li>
  <li>Members will be able to match up with friends</li>
  <li>Members can write reviews on the Bands, their music, and their events.
  
  <ul>
  <li>There can only be one review per member on a given item, although they can edit their reviews and history will be maintained.</li>
  <li>BandMembers will have the chance to write a single Comment on Reviews about the Band they are associated with. Collectively as a Band only one Comment is allowed per Review.</li>
  <li>Members can then rate all Reviews and Comments but only once per given instance</li>
  </ul></li>
  <li>Members can select their favorite Bands, music, Merchandise, and Events</li>
  <li>Bands, Songs, and Events will be categorized into the type of Genre that they are and then further subcategorized into a SubGenre if necessary. It is ok for a Band or Event to fall into more then one Genre/SubGenre combination.</li>
  <li>Event date, time, and location will be posted for a given band and members can show that they will be attending the Event. An Event can be comprised of more than one Band, and multiple Events can take place at a single location on the same day</li>
  <li>Every party will be tied to at least one address and address history shall be maintained. Each party could also be tied to more then one address at a time (i.e. billing, shipping, physical)</li>
  <li>There will be stored profiles for Bands, BandMembers, and general members.</li>
  </ol>
  
  <p>So there it is, maybe a bit involved but could be a great learning tool for many hopefully as the process evolves and input is given by the community. Any input?</p>
  
  <p><img src="https://i.stack.imgur.com/bZaDB.png" alt="alt text"></p>
  
  <p><strong>EDIT v1.1</strong>
  In response to PerformanceDBA</p>
  
  <p><strong>U.3) That means no merchandise other than Band merchandise in the database. Correct ?</strong> 
  That was my original thought but you got me thinking.  Maybe the site would want to sell its own merchandise or even other merchandise from the bands.  Not sure a mod to make for that. Would it require an entire rework of the Catalog section or just the identifying relationship that exists with the Band?
  Attempted a mod to sell both complete albums or song.  Either way they would both be in electronic format only available for download.  That is why I listed an Album as being comprised of Songs rather then 2 separate entities.</p>
  
  <p><strong>U.5)</strong> I understand what you bring up about the circular relation with Favorite.  I would like to get to this “It is either one Entity with some form of differentiation (FavoriteType) which identifies its treatment” but how to is not clear to me.  What am I missing here?</p>
  
  <p><strong>u.6)</strong> “Business Rules This is probably the only area you are weak in.”<br>
  Thanks for the honest response.  I will readdress these but I hope to clear up some confusion in my head first with the responses I have posted back to you.</p>
  
  <p><strong>Q.1)</strong> Yes I would like to have Accepted, Rejected, and Blocked.  I am not sure what you are referring to as to how this would change the logical model?</p>
  
  <p><strong>Q.2)</strong> A person does not have to be a User.  They can exist only as a BandMember.  Is that what you are asking?</p>
  
  <p><strong>Minor Issue</strong></p>
  
  <p>Zero, One, or More…Oops I admit I forgot to give this attention when building the model.  I am submitting this version as is and will address in a future version.  I need to read up more on Constraint Checking to make sure I am understanding things.</p>
  
  <p><strong>M.4)</strong> Depends if you envision OrderPurchase in the future.
  Can you expand as to what you mean here?</p>
  
  <p><img src="https://i.stack.imgur.com/klPW3.png" alt="alt text"></p>
  
  <p><strong>EDIT V1.2</strong>
  In response to PerformanceDBA input...</p>
  
  <p><strong>Lessons learned.</strong> </p>
  
  <ol>
  <li>I was mixing the concept of Identifying / Non-Identifying and Cardinality (i.e. Genre / SubGenre), and doing so inconsistently to make things worse.</li>
  <li>Associative Tables are not required in Logical Diagrams as their many-to-many relationships can be depicted and then expanded in the Physical Model. </li>
  <li>I was overlooking the Cardinality in a lot of the relationships</li>
  <li>The importance of reading through relationships using effective Verb Phrases to reassure I am modeling what I want to accomplish.</li>
  </ol>
  
  <p><strong>U.2)</strong>  In the concept of this model it is only required to track a Venue as a location for an Event.  No further data needs to be collected.  With that being said Events will take place on a given EventDate and will be hosted at a Venue.  Venues will host multiple events and possibly multiple events on a given date.  In my new model my thinking was that EventDate is already tied to Event .  Therefore, Venue will not need a relationship with EventDate.  The 5th and 6th bullets you have listed under U.2) leave me questioning my thinking though.  Am I missing something here? </p>
  
  <p><strong>U.3)</strong> Is it time to move the link between Item and Band up to Item and Party instead?  With the current design I don't see a possibility to sell merchandise not tied to the band as you have brought up. </p>
  
  <p><strong>U.5)</strong> I left as per your input rather than making it a discrete Supertype/Subtype Relationship as I don’t see a benefit of having that type of roll up.  </p>
  
  <p><strong>Additional Revisions</strong></p>
  
  <p><strong>AR.1)</strong> After going through the exercise for FavoriteItem, I feel that Item to Review requires a many-to-many relationship so that is indicated.  Necessary?
  <img src="https://i.stack.imgur.com/ZVV4I.png" alt="enter image description here"></p>
  
  <p><strong>Ok here we go for v1.3</strong></p>
  
  <p>I took a few days on this version, going back and forth with my design.  Once the logical process is complete, as I want to see if I am on the right track, I will go through in depth what I had learned and the troubles I faced as a beginner going through this process.  The big point for this version was it took throwing in some Keys to help see what I was missing in the past.  Going through the process of doing a matrix proved to be of great help also.  Regardless of anything, if it wasn't for the input given by PerformanceDBA I would still be a lost soul wondering in the dark.  Who knows my current design might reaffirm that I still am, but I have learned a lot so I am know I at least have a flashlight in my hand.  </p>
  
  <p>At this point in time I admit that I am still confused about identifying and non-identifying relationships.  In my model I had to use non-identifying relationships with non nulls just to join the relationships I wanted to model. In reading a lot on the subject there seems to be a lot of disagreement and indecisiveness on the subject so I did what I thought represented the right things in my model.  When to force (identifying) and when to be free (non-identifying)? Anyone have inputs?</p>
  
  <p><img src="https://i.stack.imgur.com/MRRA7.png" alt="enter image description here"></p>
  
  <p><strong>EDIT V1.4</strong></p>
  
  <p>Ok took the V1.3 inputs and cleaned things up for this V1.4</p>
  
  <p>Currently working on a V1.5 to include attributes.</p>
  
  <p><img src="https://i.stack.imgur.com/pboVs.png" alt="enter image description here"></p>
  
  <p><strong>EDIT V1.6</strong></p>
  
  <p>Okay, it has been some time since I have posted on here but the work on this project is still ongoing.  I am posting V1.6 now which includes a number of changes from the last posting of V1.4.  This version shows the further evolution of the Keys.  It still does not include the attributes or any AK's or IE's.  I have started working on the physical model and used that to help work through the attributes and to try and shed some light on the problems I am having with defining the AK's and IE's.  The next posting of the Logical Model will include these keys and the attributes.</p>
  
  <p><img src="https://i.stack.imgur.com/3ynZS.png" alt="enter image description here"></p>