[graphviz-interest] Problem with connecting node ports (ports unrecognized)

Hello everybody and sorry to bother you,

I have a problem connecting the ports of nodes via edges and find myself 
unable to find the error (neither by myself nor via online search) 
within the following description:

Contents of "overview.dot":

digraph top_level{

     node[rankdir = LR, shape = record]

     // node definitions
     Core[
     label = "{Core|{{\
         <p_clock> clock\l|\
         <p_reset> reset\l|\
         <p_ram_data> bootRAM_data\l\
         }||{\
         <p_ram_address> bootRAM_address\r\
         }}}"
     ]

     BootRAM[
         label = "{BootRAM|{{\
         <p_data> data\l\
         }||{\
         <p_address>address\r\
         }}}"
     ]

     Wishbone[
         label = "Wishbone"
     ]

     BootRAM:p_data -> Core:p_ram_data
     Core:p_ram_address -> BootRAM:p_address
}

Upon trying to let run dot over it, I get:

fredo in graphviz >  dot -Tsvg -o overview.svg overview.dot 
[18:19]
Warning: node Core, port p_ram_address unrecognized
Warning: node BootRAM, port p_address unrecognized
Warning: node BootRAM, port p_data unrecognized
Warning: node Core, port p_ram_data unrecognized

Can anybody help me to figure out, what is wrong?

Sincerely,
Fredo
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