Monday, February 10, 2014

Document Information Requirements Graphically With BDM Diagrams

BI teams often struggle to keep the business engaged, especially during requirements analysis. This post looks at a graphical technique for documenting information requirements -- one that business people will read and respond to.

Keeping the business engaged is one of the keys to a successful BI program. One technique I have found to be very helpful on this front is Laura Reeves's Business Dimensional Model (BDM).

The BDM is a technique for documenting information requirements. Before I explain the BDM, a few words on the requirements themselves.

Information Requirements

Before you can design a dimensional model, you need to capture the business requirements that it will support. The most successful projects capture business requirements by working directly with people in the business, often through interviews or requirements sessions.

In my book, I suggest that as you organize your information requirements by business function.  You then state them in simple form: as a group of metrics and their associated dimensionality.

For example, a set of interviews about the taking orders might boil down to a requirements statement such as:
  • Order Information by order date, order line, salesperson, customer and product.
The metrics that comprise the group are then fully documented.  For example, "Order Information" is further supported with documentation of:
  • Order dollars
  • Order quantity
  • Cost dollars
  • Gross margin dollars
  • Gross margin rate
Relevant hierarchies in the dimensions should also be specified. For example, "Product" might be described as:
  • All Products à Category à Brand à Product 
Finally, the major dimensions are cross-referenced to the metric groups in a conformance matrix.

These information requirements then drive solution modeling. The next step is to develop a top level dimensional model, and then a detailed database design.

(For more on developing and documenting requirements, including a fully fleshed out example, see my book -- it's listed at the end of this post.)

Getting People to Read It

When it comes to information requirements, you must ensure that the business stakeholders review and respond. (Better still is to involve the business in the identification and documentation process.)

In the book A Manager's Guide to Data Warehousing, Laura Reeves provides a graphical technique that helps keep the business's attention. She calls it the "Business Dimensional Model (BDM)."

This technique integrates nicely with the approach I've outlined above.

Each group of metrics is depicted in a simple diagram, with the metric group in the center and the major dimensions arrayed around it in circles.

For example, the Order Information metric group above might be documented thusly:

Within each circle, the underlined text identifies a dimension. Beneath the dimension, the level of detail applicable in the metric group is listed.

Additional illustrations document the dimension hierarchies. For example, the product dimension from the picture above might be documented like this:

The most detailed level of the dimension is shaded darkly. The arrows indicate hierarchies, going from summarized to detailed. Elements that will drive Type 2 slow changes have a shadow. Separate symbols (not shown) are used for junk dimensions, other derived elements, and future attributes.

People Like Pictures

I've found that using BDM diagrams dramatically increases the participation of business stakeholders. People look at BDM diagrams, understand them, and react to them -- often with great enthusiasm. That's a powerful aid in refining and validating your requirements.

These diagrams are also easy to produce using the built in drawing tools that come with basic productivity software.  This means you can often get business stakeholders to participate in their creation. For example, the pictures above were created in Microsoft PowerPoint using basic shapes and Smart Shapes.

Lastly, the ability to produce these diagrams using basic productivity software means they are easy to incorporate in the best format for this kind of documentation: the presentation.  I find the presentation format is far more likely to be reviewed than a word processing document. (More on this topic in a future post.)

Further Reading

As I said back in 2009, I am a big fan of Laura Reeves's approach to requirements and design. As you can see, there is a natural affinity between the BDM and the techniques I've talked about in the past.  I encourage readers to check out her book (see below).

More info about requirements and documentation can be found on this blog. Have a look at these posts:
You can read more about the process of identifying information requirements in these books:
  • The examples in this post are drawn from my book, Star Schema: The Complete Reference (McGraw-Hill, 2010)  A more fleshed out explanation of tasks and deliverables, with examples, cab be found in  Chapter 18, "How To Design and Document a Dimensional Model."  The examples from this post come from Figure 18-4 (which in turn builds on the star in Figures 3-3, and the hierarchies in Figure 7-3).
You can help support this blog by using the links above to purchase these books from

[Edited 2/13/14 - Corrected the links, thank you for the emails.]