A method and/or computer program product indicates a trustworthiness of data processed in accordance with a processing rule. A first trust weight is assigned to a data item to be processed to provide a weighted data item, the first trust weight representing a level of trust in the data item. A second trust weight is assigned to the processing rule to provide a weighted processing rule, the second trust weight representing a level of trust in the processing rule. The weighted data item is processed in accordance with the weighted processing rule to generate a data output and an indication of a level of trust in the data output.