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Data warehouses (DW) are built by gathering information from several information sources (ISs) and integrating and materializing it into one repository customized to users's needs. Some of the most recently proposed algorithms for the incremental maintenance of such materialized DWs, such as SWEEP and PSWEEP, offer several significant advantages over previous solutions, such as high-performance, no potential for infinite waits and reduced remote queries and thus reduced network and IS loads. However, similar to many other algorithms, they still have the restricting assumption that each IS can be composed of just one single relation. This is unrealistic in practice. In this paper, we hence propose a solution to overcome this restriction. The Multi-Relation Encapsulation (MRE) Wrapper supports multiple relations in information sources in a manner transparent to the rest of the environment. The Multi-Relation Encapsulation Wrapper treats one IS composed of multiple relations as if it were a single relation from the DW point of view; thus it can easily be plugged into existing incremental view maintenance algorithms without any change. Hence, our method maintains all the advantages offered by existing algorithms in the literature in particular SWEEP and PSWEEP, while also achieving the additional desired features of being non-intrusive, efficient, flexible, and well-behaved.