This paper describes the [Lscr ][Dscr ][Lscr ]++ system and the research advances that have enabled its
design and development. We begin by discussing the new nonmonotonic and nondeterministic
constructs that extend the functionality of the [Lscr ][Dscr ][Lscr ]++ language, while preserving its
model-theoretic and fixpoint semantics. Then, we describe the execution model and the open
architecture designed to support these new constructs and to facilitate the integration with
existing DBMSs and applications. Finally, we describe the lessons learned by using [Lscr ][Dscr ][Lscr ]++
on various tested applications, such as middleware and datamining.