In this work we distinguished input arcs (from a place to a transition) and output arcs (from a transition to a place) and described them separately.For simplicity, we assumed that input arcs will be used only to define numberof tokens used in firing a transition, more complex operations can be performed on output arcs using not only basic expressions but also functions. This assumption does not limit expressiveness power of TCPN and considerably facilitates simulation process. Input arcs are objects of class InputArc and hold references to the places being their sources. The InputArc class objects have also inscription attribute describing tokens that should flow through this arc while firing transitions. The inscription is a String in the format analogous to the one defined by K. Jensen [6] and describing count of tokens and variables.