1. A method for providing an XML integration grammar (XG) for mapping multiple XML sources into a single XML target, the method comprising: for each production based on a Document Type Definition (DTD) of the target, the production being associated with a parent type, automatically defining a set of rules, the defining comprising: for each child type of the production, defining a first rule for computing an inherited attribute for the child type by extracting data, via a query, from one or more DTDs corresponding to the multiple XML sources, the query being adapted to take an inherited attribute defined for the parent type as a query parameter; and for the parent type, defining a second rule for computing a synthesized attribute for the parent type by grouping synthesized attributes for all child types of the production; and storing the XIG, wherein the XIG comprises defined sets of rules.