What is a data warehouse and what does it hold?
A data warehouse is a database of your own that holds a copy of the figures from every system you run, pulled on a schedule and kept in one shape. Reconciled means the copies have been matched — the customer in Xero is the same customer as the one in simPRO and on the till — and the differences resolved by a rule you agreed, once, in writing. The store keeps every figure with its date, so last month's numbers still read the same next year. Dashboards, reports, Excel and your accountant all read from this one copy.