Since IT systems are always working on data. You MUST define some solid data principles. These principles will help you design the system and avoid complexity.
Below some examples.
Statement: Data is made available as quickly as necessary to preserve the value of the data.
Statement: Data is reasonably structured to allow automated processing.
Statement: Data is as collected at the source, with the highest possible level of granularity, not in aggregate or modified forms. Rationale
Statement: Data is available to the widest range of users for the widest range of purposes. Rationale