You have to create a new Alfresco model where you can define your own attributes. Or you extend existing an model with your attribute.
IMHO this is not directly possible yet. In a former post in this forum somebody mentioned that a service to search for content is in development. But this post was from mid summer 08...
> In your orchestration, create a new variable of type map
Can you say when this future release would be released?
is there something in progress so that custom attributes can used in queries (LC CS 8.2)?
For me it is important to retrieve all documents too, for instance for documents having a metattribute custom_id set to "12345" ... the attributes are built on a custom model.