An aircraft comprising an avionics system, wherein the avionics system comprises a first node and a second node, wherein the first node is arranged to transmit a data message to the second node, the data message comprising: a data identifier, dynamic metadata associated with the data identifier and data content; wherein the second node is arranged to receive the data message from the first node and in response to receiving the data message from the first node, the second node is arranged to: locate and read the data identifier within the data message; locate and read the dynamic metadata associated with the read data identifier; and retrieve data content from a determined position in the data message, wherein the data message contains multiple data identifiers, each with associated dynamic metadata and associated data content, and the second node is arranged only to locate and read the data identifier and dynamic metadata and retrieve data content in relation to a subset of the plurality of data identifiers, such that data content associated with one or more data identifiers that are not part of the subset is not processed, wherein the second node is configured to use the dynamic metadata to determine the position in the data message of the data content. wherein the first node is arranged to transmit a data message to the second node, the data message comprising: a data identifier, dynamic metadata associated with the data identifier and data content; wherein the second node is arranged to receive the data message from the first node and in response to receiving the data message from the first node, the second node is arranged to: locate and read the data identifier within the data message; locate and read the dynamic metadata associated with the read data identifier; and retrieve data content from a determined position in the data message, wherein the data message contains multiple data identifiers, each with associated dynamic metadata and associated data content, and the second node is arranged only to locate and read the data identifier and dynamic metadata and retrieve data content in relation to a subset of the plurality of data identifiers, such that data content associated with one or more data identifiers that are not part of the subset is not processed, wherein the second node is configured to use the dynamic metadata to determine the position in the data message of the data content. locate and read the data identifier within the data message; locate and read the dynamic metadata associated with the read data identifier; and retrieve data content from a determined position in the data message, wherein the data message contains multiple data identifiers, each with associated dynamic metadata and associated data content, and the second node is arranged only to locate and read the data identifier and dynamic metadata and retrieve data content in relation to a subset of the plurality of data identifiers, such that data content associated with one or more data identifiers that are not part of the subset is not processed, wherein the second node is configured to use the dynamic metadata to determine the position in the data message of the data content.