IMO, Since Logging is cross cutting concern, it should not refer your Data layer. In your question, I see that you had assumed that you are logging into the database. Even if this is your requirement, you have to keep database connection/insert of log records code as seperate from your application data Layer. It will be part of your Logging library rather than part of Data layer. Do NOT treat it as part of data layer. It is this perspective with which you can continue to develop/enhance logging [framework] as well as it will be seperate from your data layer.
From My perspective, data layer only constitues of Application Data Access and not logging. For concrete you can see, NLog or Log4Net libraries and see how they are not concerned with Application's data Access layer strategy.
Hope this helps.