FileInfo.com - The File Extensions Resource

.XDB File Extension

File Type	PowerDesigner Database Definition File
File Format	File
Common?	No
File Description	Contains information about a PowerDesigner database (.PDM) file; may be the default definition file included with PowerDesigner or a custom file created by the user; required for a PowerDesigner database file to open correctly.
Program(s) that open xdb files	Windows: Sybase PowerDesigner

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/xdb