diff --git a/README.md b/README.md
index 46a0c2c..ef5df95 100644
--- a/README.md
+++ b/README.md
@@ -17,38 +17,32 @@ This is free and unencumbered software released into the
 
 ## Definitions
 
-At its essence, part 5 formalizes reliable means to exchange data and commands.
-
-The initiating stations are called *primary* and the responding stations are
-*secondary*. With *unbalanced* transmission stations are either primary or
-secodary [master/slave] and with *balanced* transmission stations can act both
-as primary and as secondory [peer-to-peer].
+At its essence, part 5 formalizes reliable means to exchange measurements and
+commands. Commands are used by controlling stations to cause a change of state
+in operational equipment. Controlled stations may then optionally either
+[confirm](http://godoc.org/github.com/pascaldekloe/part5/info#Actcon) or
+or [reject](http://godoc.org/github.com/pascaldekloe/part5/info#NegFlag) the
+execution. Controlled stations can also optionally indicate completion with a
+[terminate](http://godoc.org/github.com/pascaldekloe/part5/info#Actterm).
 
-Addressing follows this initiate–respond context; an origin address remains that
-of the primary and a destination address points to (something on) the secondary,
-regardless of the message direction.
+Controlling stations are called *primary* and the controlled stations are called
+*secondary*. With *unbalanced* transmission one station is primary and the other
+is secodary, a.k.a. master/slave, and with *balanced* transmission stations can
+both act as primary and as secondory, a.k.a. peer to peer.
 
-A *common address* can be seen as a data set wherein each data element has its
-own predefined *information object address*. The set may be retreived with an
+Every *information object address* resides in a *common address*. Primaries may
+acquire the information present in a common address with an
 [interrogation command](http://godoc.org/github.com/pascaldekloe/part5/info#C_IC_NA_1).
+E.g., run `iecat -host station1.example.com -inro 42` to aquire a listing of
+common address 42 on the terminal.
 
-The standard provides commands that operate on data and they may trigger remote
-procceses by agreement. Again, each command is applied to a single information
-object address. Secondaries either
-[confirm](http://godoc.org/github.com/pascaldekloe/part5/info#Actcon) or
-[reject](http://godoc.org/github.com/pascaldekloe/part5/info#NegFlag) execution.
-Optionaly the command may indicate completion with a *terminate*
-[message](http://godoc.org/github.com/pascaldekloe/part5/info#Actterm).
-Some commands can be preceded with a *select*
-[directive](http://godoc.org/github.com/pascaldekloe/part5/info#Cmd.Exec)
-which locks down processing to one at a time.
 
+## To Do
 
-## TODO
+The following is not implement yet.
 
-* file transfer
-* parameters
-* complete ASDU encoding types
+* file transfer, type identifier F_*
+* parameter of measured value, type identifeir P_*
 
 
 ## iecat