I installed the DevExpress demo
C:\Users\Public\Documents\DevExpress Demos 15.2\DevExtreme\DXHotels
The demo came with HotelDB.mdf in the App_Data folder.
Out of curiosity I attempted to open the HotelDB.mdf by attempting to attach it using SQL Server 2012 Express Management Studio
However I got an error about a missing log file when I did this.
When I ran the application from the solution the log file created and I was able to subsequently attach using SQL Server.
Why was the application able to open the file when Management Studio could not?