[Quickfix-developers] Help: Securities can be specified either by ID or by description

[George <pap...@gm...>]

Hi,
Securities can be specified either by ID (tag 48) or by description (tag 55)
Let's say i would like to buy "EUR/USD". 
If i specify the security by symbol, i will just add 55=EUR/USD
How can i specify the security by id?
Could anyone give me an example?
Not that i am interested about currency...

Thank you.