[rules-users] How does drools loads a modified rule ?

Hi All, I am new to Rule Engine concept. I am investigating the Drools 5.0 to check if it meets our requirements. Questions: 1. I am not able to find a resource to learn the syntax of drool rules. I have gone through the shopping example in Drools 5.1 examples but not able to get the basics right. $c : Customer() -- what does this mean ? Is it that all objects of type Customer in the working memory are matched are taken one by ones and assigned to c ? $d : Discount( customer == $c ) -- Each discount objects which have the matching customer are assigned to d. How can I debug this process in eclipse ? Please provide a resource where I can learn the drl syntax. Also what are differences in drl when dialect is java and not mvel. 2. How would a rule engine behave when rules are running on the facts and simultaneously the rules are updated in the knowledge base?