sysdbql(7): Document typed expressions.

diff --git a/doc/sysdbql.7.txt b/doc/sysdbql.7.txt
index 7ed9a11ec61baf7ad6b9db02b70b7d26465cb639..9a16e23a4593f58f7ca582728e4828b6d68205aa 100644 (file)
--- a/doc/sysdbql.7.txt
+++ b/doc/sysdbql.7.txt
@@ -177,6 +177,15 @@ The following fields may be queried:
        an attribute value with some other value, the two values will be cast to
        strings before comparing them.
 
+Field expressions may be applied to parent or child nodes. For example, a
+host's services are child objects and the host is the parent of the service
+objects. This is done using typed expressions:
+
+host|service|metric.'<field>'::
+       Evaluate the field in the context of the respective parent or child.
+       Currently, this is limited to services or metrics referencing their parent
+       host.
+
 The following logical operators are supported by SysDB. Unless otherwise
 noted, the data types of the left hand and right hand side have to match.
 
@@ -200,7 +209,7 @@ noted, the data types of the left hand and right hand side have to match.
        Checks whether a value compares less than, less than or equal to, greater
        than or equal, or greater than some other value.
 
-The following arithmetic operators are supported by SysDB. Unless otherwise 
+The following arithmetic operators are supported by SysDB. Unless otherwise
 noted, the data types of the left hand and right hand side have to match.
 
 *+*::