Data modeling has always been about telling a story. Before the arrival of entity relationship diagram (ERD) in the mid 70s, the data story was told using flowcharts and file layouts. I remember my early programming days where I used a handy dandy IBM flowchart template to meticulously flowchart the movement, interaction and transformation of data. Data files were documented on file layout sheets. It was a highly manual process with the resulting flowcharts and file layouts filed in documentation binders and hardcopy run books.
With the advent of relational database design, the Entity Relationship Diagram (ERD) made its debut. The ERD gave us the ability graphically depict data and the relationship data had with other data. It was a breakthrough in telling the data story. Run books and flowcharts were very much in the realm of the IT staff. You might have encountered a business user who was interested in paging through these sheets to understand an application. This was typically not the case. We could finally tell the story to our business users in a graphical manner.
How good of a story teller are you? The data story is not told in books but is told through the layout, appearance and format of your data models. How effective a communicator you are very much depends on your talents on making your data model readable and understandable. Subject areas and stored displays are techniques that I feel make a good data model a good story.
This technique is in the back pocket of all data modelers. We all know the value of taking a smaller bite of our data model to more effectively communicate the data story. I use subject areas in a variety of ways.
- My subject areas define the specific business domains within my enterprise.
- I use subject areas show how entities work together to solve specific business questions.
- I like to define a neighborhood view of all entities related to a core business entity.
- I build subject areas to answer specific questions a developer or business partner may have.
Subject area tips:
- It should fit on a standard sheet of paper in a size and font that is readable.
- Keep out the noise. i.e. Chose entitles wisely and limit how many; usually less than 20.
- Use color to show business domain ownership. Provide a legend to help readers navigate.
- Add freeform text to highlight or explain a critical or difficult to understand concept.
Building stored displays is a handy feature in ERwin that I use to target the data models and subject areas to specific audiences. I have observed that it is often misunderstood and underutilized in our community. Many people confuse it with subject area modeling. As a standard practice, I build three stored displays for each of my data models and subject areas.
- Conceptual – This display is set to the logical model with the display level set to Entity and the keys checked in the Entity Display. This display is useful in reviewing your design at high level with the business community. I use it more in the requirements and analysis phases of a project.
- Logical – I set the display to the logical model and the display level to Attribute with the keys checked in the Entity Display. This is a good view to use when firming up attributes with your business users in the analysis phase of a project.
- Physical – I set the display to the physical model and the display level to Column and everything checked in the Table Display. Developers love this view that is used mostly in design and construction phase of a project. It’s the layout of the database that they hang on their cubicle wall.
Subject areas and stored displays are perhaps the most powerful tools you have in your arsenal. They help you tell your storey more effectively by targeting specific business topics and solutions in your diagrams. Remember that to tell a story effectively, you need to talk the language of your targeted readers. Controlling the display very much makes that doable. I hope that you are using these techniques today when working with your clients. If you are not, I encourage you to give one of these techniques a try. I think you will be happy with h the results.
Until next time…
Modeling Global User Community President
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