I was showing examples of both complete and incomplete definitions during a recent training class when I shared the following incomplete definition for a customer identifier: a customer identifier is the unique identifier for a customer. “What else can you say about customer identifier anyway?” a participant asked.

The Response

There are three terms within this definition that require an explanation: “unique,” “identifier” and “customer.”


The term “unique” is ambiguous and could easily be interpreted differently by readers of this definition. To maintain clarity and correctness, these questions should be answered within the definition:

Are identifier values ever reused? Bruce Baum, global data architect, and Bob Mosscrop, enterprise data architect, both mention this as a critical question to answer in this definition. Two or more customers might share the same identifier after a certain amount of time elapses, due to database or system limitations, or as a result of faulty business processes. It is important to mention whether this can happen and the specific circumstances when it can happen. Gordon Everest, professor emeritus, provides this example: “If a customer ceases to be a customer, such as they go out of business, is their ID ever reused? If yes, after how long of a waiting period?”

What is the scope of uniqueness? Norman Daoust, business analyst consultant, recommends mentioning the scope of uniqueness within the definition. That is, whether the identifier is unique just within a specific system or department, just within the assigning organization or country, or globally unique.

How is the identifier validated? Joe Celko, author/consultant, recommends addressing these questions: “How do you validate and verify the customer identifier? Is there an industry standard for it? For example, DUNS number if the customers are businesses and bar number if the customers are lawyers.”


We can describe the actual identifier in more detail, including addressing these areas:

Purpose. Richard Leach, data consultant, would include the reason why the identifier is needed. For example, perhaps the identifier is needed because there are multiple source systems for customer data, each with their own ID. To enable a common set of data to be held about them, this identifier needed to be created to facilitate integration and guarantee uniqueness across all customers.

Business or surrogate key. Georgia Prothero, data modeler, suggests mentioning within the definition whether the identifier is meaningful to the business (i.e., the business or natural key) or whether it is a meaningless integer counter (i.e., the surrogate key).

Assignment. Andrew Knapp, data architect, and Scott Meredith, IT architect, both recommend mentioning how a new customer identifier is assigned. Scott says, “One needs to include verbiage which identifies the business criteria under which a new unique customer identifier value is generated. This criteria is a listing of elements that truly differentiate one customer from all others.” The party that is responsible for creating new identifiers should also be mentioned.

Usage. Terry Gaspari, data modeler, believes it is valuable to also mention whether the identifier is used on screens or reports by business users or whether it is strictly for processing purposes behind the scenes.


Many of our Challengers recommend explaining what we are identifying, in this case, “customer.” Carol Lehn, senior database designer, says, “For all unique identifiers, I use a description of what the thing is as part of the definition, using all or part of the entity definition in the definition of its identifier.” Barbara Nichols, data and metadata management consultant, would also include the concept of “role.” For example, whether the customer role can overlap with other roles such as vendor and employee.

Lee LeClair, senior system engineer, would define customer identifier as: “An arbitrary set of characters that is used to uniquely identify (and refer to) a specific person or organization that currently purchases our company product(s) or has done so in the past.” Mattie Keaton, logical data modeler, has a similar definition: “A unique identifier generated by a system and assigned to an organization or an individual who has purchased our products or services as well as those having the potential to do business with us in the future.” Lori Russell, data architect, would include this definition of customer: “Customer is the recipient or purchaser of our finished products, one that acquires goods or services either for direct use or ownership, or for resale.”

If you would like to become a Design Challenger and have the opportunity to submit modeling solutions, please add your email address at http://www.stevehoberman.com/. If you have a challenge you would like our group to tackle, please email me a description of the scenario at mailto:me@stevehoberman.com

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