Success factors and pitfalls of declarative approaches

Declarative programming may not seem to be widespread, but it has been used for several decades in some areas of information technology. Examples are SQL for querying databases, and regular expressions and grammars for text analysis. More recently, domain-specific languages have been used to take advantage of declarative methods, with varying degrees of success. What can we learn from the successful applications of declarative programming? And perhaps more importantly, is there something that failed applications have in common? In this presentation we will look at declarative techniques that are so ubiquitous that nobody notices them anymore. We will also look at two pitfalls that the author has encountered many times: genericity and reification.