XML has replaced traditional EDI standards in the field of business document standardization. Despite of the syntax, the principal approach to develop business document standards has not changed. A standardized business document is built by a superset of all elements that may appear in any business context, leading to overloaded and complex standards. However, in a particular partnership only a small percentage of the elements is used. This results in a top-down approach starting from a generic document and specifying partner-specific subsets. Such an approach is too costly for small and medium-sized enterprises (SME), because agreements on subsets must be implemented in their software systems. As an alternative we suggest a bottom-up solution that starts from a core set of elements, representing the intersection of all industry contexts. Thereby, the core set may be extended to incorporate the needs of a specific business context. In this paper we examine different mechanisms provided by XML Schema to realize such an extension. The applicability of the different mechanisms is evaluated by means of the Austrian e-Invoicing standard ebInterface, which we co-authored.