I am working on an application which converts from our Document Object Model into a Policy and then import that policy into BizTalk Business Rule Engine.
Does anyone where can I find the specification for BRL (Business Rule Language) which is used for importing and exporting policies ?
Sorry, no. The spec, schemas or otherwise, are not published.
You would have to develop by example. On other words, export a Policy with the pattern you're interested in to see how it's composed.
However, Policies are actually created through an API which would technically be the correct way to do it. See: Microsoft.RuleEngine
The HelloWorld examples in the SDK folder demonstrate how to get started.