CASE stands for Computer-Aided Software Engineering. Here, I’m referring to data modeling tools like ErWin and ER/Studio. It disheartens me that the industry as a whole has gotten away from using these tools. In this world of rushing software to market, we’ve forgotten that the data-driven marketplace starts with the word ‘data‘.
A brief history of CASE
I started in IT in the 90s when things moved a little slower and we actually took time to model databases. [Editor: I somehow managed to resist inserting a gif of an old man and a cane.] So, I got used to using CASE tools, and by the year 2000 I was quite adept at using the different flavors of these tools. And I’m going to tell you, I miss them greatly.
The word domain has had a lot of play in IT, because it’s a nice generic container for many things. In the 1990s, a domain was a universal concept when working with a CASE tool. In SQL, we have another word for domain: column. Old timers like Joe Celko get really irate when you call a domain a column, because they know what it’s for. But we’ll get to that in a minute. First, let’s talk about the difference between a domain and a column.
Column vs Domain
A column is a single property in a table, which holds the same type of data throughout all rows. Think of an Excel spreadsheet that stores a list of names. That’s how data is represented to us, even in SQL Server Management Studio (and practically every other query tool out there). We see the data as these little on-the-fly spreadsheets. But, that would be a very myopic view of what a domain is.
In data modeling, a domain is implemented as a column. But, the domain itself is an organizational structure for column definitions. A single domain can apply to individual columns in dozens of tables, if you like. Let’s take an example.
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