Currently I'm involved in a project with lots of rules in it. There's an idea to use BizTalk's Business Rule Composer for rule creation.
Question1. Is it possible to use it independently?
Question2. If so, how can I subscribe to change of different Fact Source types like .Net Objects, Databases?
FYI, I'm using BizTalk Server 2013.
On
A1: Yes. The BRE has a full C# API and can be used independently of BizTalk Server. You can find the API docs with C# examples here: http://msdn.microsoft.com/en-us/library/aa561833.aspx
A2: Keeping Facts current is something to decide on a case by case basis. For Long Term Facts, you Fact Retrieve can be programmed to detect any changes (there's no way to just 'know') and update it's Facts. Similarly, .Net Facts can programmed to keep them selves current.
For clarity, you can install the BRE without BizTalk Server, they are actually separate stacks. However, you still require a BizTalk Server License for any machine where the BRE will run.
Well, to run the rules composer you need to have the biztalk engine installed, you can't separate them, in such a case you will end up to pay for the license of biztalk to have the rules engine composer.
Why not to use another product? I think there is some products concerned for business rules engines that you can use and for workflow as well. If you want a free one you can have Worlflow 4.0 for microsoft (doesn't include business rules engine but you can implement one using the specification pattern - by code). Other paid products such as K2 blackpearl might help as well check them out.