Cash data represents the recording of economic events at the time when the cash payment related to that event had occurred. In other words, it will record revenue and receipts in terms of asset and liability transactions when the actual cash moves. In terms of the coverage of transactions, the cash basis of accounting would only record transactions if it represented some kind of a cash flow - in other words, events such as donations in kind and debt forgiveness will not be recorded in a cash-based system since it does not represent any cash flows.
Accrual data represents the recording of economic events at the time the economic value was created, transformed, exchanged transferred, or extinguished. In other words, the economic events are recorded in the period in which they occurred, irrespective of whether cash was received or paid. In terms of coverage of transactions, an accrual basis of accounting would record all economic events, and would therefore include the value of transactions in kind (example: donations of food) and events such as debt forgiveness.
From the above explanations, one should not add these two values or mix cash and accrual data, because the two systems are reporting the same events, albeit at different times. Traditionally, the majority of governments recorded their government accounts only on a cash basis, however, modern thinking about fiscal management, and also, the GFSM proposes that governments record cash transactions in a Statement of Cash Flows to have information available on the liquidity of government finances, and also, to record accrual accounts to get an indication of the full spectrum of governments fiscal position. In the latter, transactions such as services received by government, but not yet paid and commitments such as government employee pension obligations would be included - these data could therefore differ significantly from the cash data.
More information on GFSM can be found here.
The GFS dataset can be found here.