Will DSLs allow business people to write software rules without involving programmers?
When people talk about DSLs it's common to raise the question of business people writing code for themselves. I like to apply the COBOL inference to this line of thought. That is that one of the original aims of COBOL was to allow people to write software without programmers, and we know how that worked out. So when any scheme is hatched to write code without programmers, I have to ask what's special this time that would make it succeed where COBOL (and so many other things) have failed.
I do think that programming involves a particular mind-set, an ability to both give precise instructions to a machine and the ability to structure a large amount of such instructions to make a comprehensible program. That talent, and the time involved to understand and build a program, is why programming has resisted being disintermediated for so long. It's also why many "non-programming" environments end up breeding their own class of programmers-in-fact.
That said, I do think that the greatest potential benefit of DSLs comes when business people participate directly in the writing of the DSL code. The sweet spot, however is in making DSLs business-readable rather than business-writeable. If business people are able to look at the DSL code and understand it, then we can build a deep and rich communication channel between software development and the underlying domain. Since this is the Yawning Crevasse of Doom in software, DSLs have great value if they can help address it.
With a business-readable DSL, programmers write the code but they show that code frequently to business people who can understand what it means. These customers can then make changes, maybe draft some code, but it's the programmers who make it solid and do the debugging and testing.
This isn't to say that there's no benefit in a business-writable DSL. Indeed a couple of years ago some colleagues of mine built a system that included just that, and it was much appreciated by the business. It's just that the effort in creating a decent editing environment, meaningful error messages, debugging and testing tools raises the cost significantly.
While I'm quick to use the COBOL inference to diss many tools that seek to avoid programmers, I also have to acknowledge the big exception: spreadsheets. All over the world suprisingly big business functions are run off the back of Excel. Serious programmers tend to look down their noses at these, but we need to take them more seriously and try to understand why they have been as successful as they are. It's certainly part of the reason that drives many LanguageWorkbench developers to provide a different vision of software development.