Names of helpKey properties files are arbitrary (as long as they end with .properties). However, a context-sensitive help plug-in could contribute pairs of helpKey properties files for several UI plug-ins, and the files would need to have unique names, if they were located in the same directory.
To allow arbitrary names for helpKey properties files, and to abstract the names of helpKey properties files from UI components, the DTP help-helper provides an extension point (org.eclipse.datatools.help.helpKeyProperties). That extension point allows any plug-in to declare helpKey properties file contributions for a UI plug-in.