An optional clause in the Data Providers declaration allows us to define the Transaction (or Transaction level) that we want to use as Base Table for the Data Provider navigation.
See Base Transaction clause for more information about Base Transaction concept.
The way to define the Base Transaction in a Data Provider is by using the FROM clause into a Data provider Group statement.
InvoiceItem From Invoice
Date = today()
Invoice from Invoice
Where InvoiceDate = today()
Id = InvoiceId
CustomerId = ClientId
CustomerName = ClientName
Amount = InvoiceTotal
Id = ProductId
DetailQuantity = InvoiceProductQty
DetailAmount = InvoiceProductPrice