Tuesday, January 1, 2013

An old SQL Server Interview Question: What are Crow’s Feet?

I recall being asked that question at an interview long ago. In the circles that I had been working we had never used that (academic) term and had been using the diagramming tools in SQL Server Management Studio(SSMS). It was simply what we used. So what are crow’s feet?


It is a diagramming notation which, incidentally, is not supported in SQL Server Management Studio but is supported in third party tools. Since I had been working for Microsoft’s ITG SQL Server Team for several years prior without any third party tools --- I could not return a snappy answer. The origin of this was that the early adapters moved to Oracle, so this because an attitude issue with Microsoft.


Today, crow’s foot notation has become the non-Microsoft industry standard in stead of SSMS infinity key notation. The comical thing is that Microsoft Visio does support crow’s foot notation. A few example tools that uses this notation are: ARIS, System Architect, PowerDesigner, Toad Data Modeler, DeZign for Databases, Devgems Data Modeler, OmniGraffle, MySQL Workbench, SQL Developer Data Modeler and Information Engineering Facility.


For some short academic summaries see:

The difference is shown below, my own preference is still to use the  0…n: 0…n style notation because it is far easier to read by the user. For example, when you are doing a data model review. The use of crow’s foot notation creates obtuseness (and potentially misunderstandings and thus mis-implementations).





I did not get the job, likely because the interviewer used a “culturally bias” question. If he had asked me to diagram out a relationship, he would have seen that I used standard Microsoft DBMS diagramming notation instead of Oracle’s.

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