Please first read the "Mapping Global Variables" and "Mapping Facts" sections of the Rules Services documentation:
https://docs.jboss.org/author/display/SWITCHYARD/Rules+Services

Tooling clarifications:
1. Both the <globals> and <facts> elements are optional.
2. Both the <globals> and <facts> elements take 0..* <mapping> elements as children.
3. The "expresssion" attribute of the <mapping> element is required for both the <globals> and <facts> elements.
4. The "variable" attribute of the <mapping> element is also required for just the <globals> element. It is meaningless with regard to <facts>.
5. The "expression" value can be rooted via either a context, message or exchange.
6. The "expressionType" attribute of the <mapping> element is optional, however the only supported value at this time is MVEL.
7. The "contextScope" attribute of the <mapping> element is optional, however it can be IN, OUT or EXCHANGE. The default value is IN.