The transactional currency in tandem with the order matching algorithm enables a very indirect association between buyers and sellers. In the below diagram the person who has currency E wants to trade for currency F, but the person who holds currency F wants currency B and not currency E etc. Via the use of DEX all the trades are able to happen with the exception of the person who holds currency C and wants currency B; As there is no one else on the exchange who wants currency C, regardless of what it is being traded for.
