Hi Subramanya,
there is no specific syntax for in/out parameters. Whether a parameter is input and/or output depends on how the unit/rule is used. For example, consider you have a rule with a parameter "x" which should be equal to a "name" attribute of a node in the rule. If you assign a value to this parameter before the rule application, the rule will find the node with this name. In this scenario it is basically an input scenario. If you do not specify a value the rule will match all corresponding nodes and essentially produce all possible values of names as outputs.
If you are using the graphical editor, the parameter passing is defined by the name of parameters. Say the first rule has a parameter "x". If you want to pass it to the third rule, simply call the parameter of the third rule also "x". In the tree-based editor you have a more fine-grained control. There the parameter passing is modeled using ParameterMappings. Maybe it helps if you play around with it in the graphical editor and then open the *.henshin file to see the model that is been produced.
Cheers,
Christian
