Ancillary data is adjunct information used in the formulation of transactions. It differs from transaction data because it is not used to define the operation described within a transaction. Probably the best way to explain ancillary data is by using examples.
TRANSFER 500 USD to 1 Bitcoin in MyAccount
TRANSFER 200 AMZN Shares from MyOrg to YourOrg
Some DIDO implementations may provide direct support of ancillary data within the DIDO or they may provide access to external ancillary data through oracles. However, if ancillary data is not also implemented within the DIDO, but implemented externally with and accessed through the use of oracles, many of the benefits of the distributed architecture are lost because access to the ancillary data can become a bottleneck.