If there is a tool every business person—from a CEO to a secretary—knows how to use, it is a spreadsheet. In fact, most of the time, they know more about spreadsheets than most people in the IT department. If one of the goals of Drools is to be a business-oriented rule engine, then what could be better than to provide first-class integration with spreadsheets?
DSLs are very powerful, but, without a proper UI, the users still need to write their rules by themselves. Even if, by using a DSL, the available options to write rules are narrowed down to very specific sentences, the probability of syntax errors, misplaced statements, invalid code, and so on is still high.
Decision tables, on the other hand, provide a much more constrained environment than DSL, thus mitigating most of the risks DSL has.