By Caryn Maresic, Senior Consultant

Logical Data Models (LDMs) were the standard means of recording business rules and data definitions back in the β€˜80s and β€˜90s.  Business and IT partnered to learn the art of data modeling and 3rd normal form in hopes of finding a common ground to record requirements.  Over time, it became evident that in today’s fast-paced development environment the business doesn’t have the time to digest all the nuances in a data model.  It is IT’s job to gather information via interviews.  Many times, we skip the LDM task because we don’t have time and LDMs are too academic and we find ourselves asking...

Are Logical Data Models really necessary?  Yes!

LDMs drive BI design by defining business rules independent of physical implementation.  There are many tools (CA ERwin Data Modeling, Embarcadero Technologies), and techniques (UML, IDEF, Bachman) in use today. To illustrate the difference between the benefits of a PDM and an LDM, let’s look at an example:  Customer/Address relationships.

The PDM above (created using) supports many Customer/Address business rules, but it does not tell me the Customer/Address relationships as defined by the business.

In contrast, the following LDM is more rigorous and definitive:

What does the LDM above tell me that the PDM did not? 

• There are two types of Addresses – Physical and Mailing.
• The Customer Bill To Address can be either a Physical or Mailing Address
• Customer Ship To Addresses must be Physical Addresses.
• Every customer must have a Bill To Address.
• A Customer has zero, one or many Ship To Addresses.

All of these relationships can be implemented using the PDM, but they aren’t dictated by the PDM.  The LDM explicitly defines each relationship and prompts us to ask better questions of the business, such as:

• Are there any Customers who do not have a Bill To Address?
• Are there any Customers who do not have a Ship To Address?
• When there are multiple Ship To Addresses, how do you know which one to use?
• Are there any Customers who have more than one Bill To Address?
• Do you know of any upcoming business initiatives that might change these rules?
• Was there ever a time when the business rules were different?

The answers to these questions may require changes to the model, but without the LDM, we may not have asked the right questions!  The best part about the LDM is how valuable it is to the rest of the development process.  It will be used in production of training materials, test plans and test cases, data profiling and migration efforts and, finally, physical database design.

Caryn has over 20 years experience in providing high-quality data solutions to clients in the areas of Business Intelligence, Data Warehousing and System Integration.  Caryn has expertise in across industries with an emphasis in Pharmaceutical, Manufacturing, and Insurance.  Prior to joining to Baseline, she ran her own consulting company.