Management Information System

12 Responses to “Logic Data Modeling 9 – Entity Relationship Diagram, part 2”

1. gvimontslice on October 16th, 2009 at 8:10 pm

   (2) Add a data mart …
   (2) Add a data mart: Very popular these days, a variety of data warehousing techniques and technologies can be employed to record this historical perspective on data values without encumbering the operational data store (the transactional Order-Items model) with additional triggers or stored procedures. Data marts tend to leverage dimensional designs such that reporting performance may be significantly better than tapping the operational data store for the same historical information.

2. gvimontslice on October 16th, 2009 at 8:10 pm

   (1) Add another …
   (1) Add another entity: Add a new entitiy called Item History. Any time any of the attribute’s values are changed, a new time-and-date stamped record will be recorded within this entity’s table. By doing so, you’ll be able to reconstruct the entire life of the item: all of its pricing history and the dates when the price changes occurred.

3. gvimontslice on October 16th, 2009 at 8:10 pm

   Let’s extend the …
   Let’s extend the scenario that you’ve just described to include other attributes of the item entity. What if any of the attribute’s other value change with time. There are two primary means of addressing this: (1) Add another entity to capture history. (2) Create a data mart.

4. twbowskill on October 16th, 2009 at 8:10 pm

   Just watched these …
   Just watched these lectures; I must say that they are very articulate and informative. I do have one query though (pun unintended!)

   Say, for example, an item was reduced from £30, to £10 for a short period of time before going back up to £30 again. A few months later it goes back to £10 – not uncommon.

   Let’s say that the firm wanted to see how well the item sold in the first period of time. To do this we need some way of also storing the time period when the first sale was on…

5. programatic on October 16th, 2009 at 8:10 pm

   after 2 year, I …
   after 2 year, I finally learned how to normalize!!!

6. gvimontslice on October 16th, 2009 at 8:10 pm

   Likewise, over time …
   Likewise, over time, there may be many orders that have different prices recorded for the same item. These different prices will be captured within the Order Item Price attribute.

7. gvimontslice on October 16th, 2009 at 8:10 pm

   Order item price is …
   Order item price is an attribute that will record the actual value of the item’s price as it is applied to a specific order#. Think of it this way: Over time the item price may change. If the item price changes, then there is now means by which to determine the price that was applied within a specific order#, save for the Order Item Price attribute.

8. gvimontslice on October 16th, 2009 at 8:10 pm

   Physical data …
   Physical data modeling is supported directly within SQL Server and MS Access. MS Visio professional provides logical and physical data modeling with the option to display models with crows foot notation. JUDE professional now provides both Data Flow modeling and Data modeling in addition to UML modeling. High-end tools include, System Architect (IBM/Telelogic), Rational Data Architect (IBM), ERWin, TOAD Data Modeler (Quest) and ER/Studio (Embarcadero).

9. NajanJan on October 16th, 2009 at 8:10 pm

   could you introduce …
   could you introduce a s/w which i can draw the ERD?
   I’m just learning this and would like to use a s/w to draw them and get more help.
   I appreciate your help or suggestion on this.
   thanks

10. gvimontslice on October 16th, 2009 at 8:10 pm

    For part 1 of this …
    For part 1 of this section, look for: Logic Data Modeling 8 – Entity Relationship Diagram, part 1

11. a7la6eer on October 16th, 2009 at 8:10 pm

    Thanks for posting …
    Thanks for posting this lecture.

12. ironbutterfly76 on October 16th, 2009 at 8:10 pm

    This was a big help …
    This was a big help in understanding normalization. Thanks for posting!

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