get order data from live cache

Hi, experts.

I need to get sales order and purchase order from live cash. And after some research I find the function module /SAPAPO/OM_PEGID_GET_ORDERS which could get orders by pegid, but I am confused by the parameters. What is the data returned from tables ET_ACTIVITIES(Table of Activities),ET_INPUTS(Table of Input Nodes),ET_OUTPUTS(Table of Output Nodes)?  What is input node? What is output node? What is the relationship between input node and output node?

Thanks in advance.

Loring