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       elektra-cascading - of key names

       Cascading  is  the  triggering of secondary actions. For configuration it means that first
       the user configuration is read and if this attempt fails, the system configuration is used
       as fallback.

       The  idea  is  that the application installs a configuration storage with default settings
       that can only be changed by the administrator. But  every  user  has  the  possibility  to
       override  parts  of  this  system  configuration  regarding  the user´s needs in the *user
       configuration. To sum up, besides system configuration, users have their own key databases
       that can override the settings according to their preferences.

       Thus when a key starts with / such cascading will automatically performed.


       Keys in spec allow us to specify which keys are read by the application, which fallback it
       might have and which is the default value using meta data.  The  implementation  of  these
       features  happened  in  ksLookup.  When  cascading  keys  (those starting with /) are used
       following features are available (in the meta data of respective spec-keys):

       ·   override/#: use these keys in favour of the key itself (note that # is the syntax  for
           arrays, e.g. #0 for the first element, #_10 for the 11th and so on)

       ·   namespace/#:  instead of using all namespaces in the predefined order, one can specify
           which namespaces should be searched in which order

       ·   fallback/#:  when  no  key  was  found  in  any  of  the  (specified)  namespaces  the
           fallback-keys will be searched

       ·   default: this value will be used if nothing else was found


       When  cascading keys (those starting with /) the lookup will work in the following way (it
       can be debugged with kdb get -v):

       1.) In the spec-key the override/# keys will be considered. 2.) If,  in  the  spec-key,  a
       namespace/#  exist,  those  namespaces will be used. 3.) Otherwise, all namespaces will be
       considered, see here. /doc/help/ 4.) In the spec-key  the  fallback/#
       keys will be considered. 5.) In the spec-key the default value will be returned.

       See  application  integration  /doc/tutorials/  for  how  to use
       cascading names in the context of applications.

       Read more about namespaces. /doc/help/

                                          November 2015                      ELEKTRA-CASCADING(7)