Traditional workflow management technology can deal with pre-defined business processes well. However, a practical ad-hoc process case in knowledge-intensive domain is often driven by not only process control, but also the real-time application data or user interactions. So the structure of those processes are hard to be completely fixed ahead. In addition, as the only basic element in traditional process, task, is often too coarse or too fine in real applications. Even though the process structure could be pre-defined completely, there is only a non-declarative way to build the process by traditional methods. To solve the above problems, we developed a declaratively constructing environment, named PASE. We propose a multi-layer model to percept ad-hoc process. And we adopt a transformation strategy to translate the model to process specifications based on logic reasoning and calculus. We also provide a graphical tool to help user construct information systems declaratively.