If you had just started OAF development,you would have come across the word DBC file.You have to refer this file in OAF runtime connection in JDEV.There are two ways to get this file to your local machine.
1) Get it from server path $INST_TOP/appl/fnd/12.0.0/secure for R12 or $FND_TOP/secure for 11i.
2) In some cases you may not have the access to the server.You can get the content of the dbc file from below URL.
Replace host name and port with yours.
Please refer below screenshots: