Prerequisites: PC with Visual Studio 2010 with SP1.
Download SSDT setup from MSDN SQL Server Data Tools
After download has finished run SSDTSetup.exe
This takes a long while, , VS2010 starts (did I start this accidentally while doing other work or was it the installer?) Minimizing the installer window works, but maximizing again does not work; although it still seems to be active.
Result: An important prerequisite is the installation of SQL 2012 Standard or higher and not mentioned by the site. SQL Express is not sufficient.
since none of my customers are using SQL 2012 I did not install it either. To be continued.