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Understanding a Database

This editorial was originally published on Nov 30, 2018. It is being republished today as Steve is traveling.

I ran across a post that asked a good question, one which I want to ask you today: how do you learn about a database?

I've run into quite a few databases in my career. Some were third party systems, like Dynamics and JD Edwards World. Some were databases that custom designed and built by developers and database modelers of widely varying skills. Some were well built in order to normalize data and define referential integrity, and other databases were put together in a piecemeal fashion over time, lacking keys and consistent naming. I'll leave it to you to guess if there were more of the former or the latter.

When a developer or DBA comes across a database, what's the way that they can decode what fields and columns mean? Certainly names help at times, especially when the purpose of the database is understood, but all too often the names don't quite make sense. This is especially true in many vendor databases. The one common theme I've seen in many databases is that there is no data dictionary provided by anyone.

Trying to understand a database has been a trial and error detective task for me in the past. Usually this starts when I need to do some work that is requested by users: write a report, change data, etc. In these cases, I often will ask users to access certain data related to the change from their application while I run Extended Events and note which entities are accessed. I can then start looking for data elements, and note which columns might be mapped to which fields in an application.

Often I've built a data dictionary of sorts outside of the database using something like ErWin, ER/Studio, or another tool. That has been somewhat flawed, as it's hard to share the information with others. These days I think I'd make extensive use of Extended Properties to document what I learned, so that all my knowledge is available for anyone else that needed to work on the system. They can just look at the properties for various entities.

If you've got other methods, share them with us today. I'm sure there are plenty of DBAs and developers out there that would like some tips and tricks for decoding a database design.

Steve Jones - SSC Editor

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