1. A computer implemented method for processing data for a spreadsheet system model, comprising: providing a spreadsheet model specification in a computer system with a plurality of item types which may potentially be provided in the spreadsheet, including: at least one first-type item for which input data is put into the computer system to indicate that said first-type item can be included in the spreadsheet; and at least one second-type item, wherein second-type items are putatively determinable from one or more operations performed on data stored in a first database, and wherein second-type items are included in the spreadsheet if ascertained to be determinable; putting said input data into the system; searching, using a processor for the computer system, the input data for a first-type item; storing said first-type item found by the searching step in the first database, performing an iterative process to ascertain whether the first database includes one or more prerequisite items needed to determine a putative second-type item, wherein: (a) each iteration comprises successively reading putative second-type items and ascertaining whether the first database includes prerequisite items sufficient to determine said putative second-type item, and if the first database does include prerequisite items sufficient to determine said second-type item, automatically storing that second-type item in the first database, such that said second-type item becomes available as a potential prerequisite item for other putative second-type items in subsequent iterations; (b) the iterative process is automatically terminated when an iteration fails to store a second-type item in the first database which was not stored there in a previous iteration, thus indicating that all putative second-type items logically determinable from said stored data have been determined and stored in the first database; and (c) re-assessing in each iteration putative second-type items that could not be determined in previous iterations due to lack of a prerequisite item, by taking into account second-type items stored in the first database by previous iterations; and outputting an indication that the spreadsheet system model can be produced if items of the model specification are stored in the first database.