Data Warehouses and on-line analytical processing (OLAP)  systems are a promising area for the application of Abstract State Machines  (ASMs). In this paper a ground model specification for data warehouses  is sketched that is based on the fundamental idea of separating  input from operational databases and output to OLAP systems. On this  basis we start defining formal refinement rules for such systems. These  refinement rules enable a formal method for the design of data warehouses  and OLAP systems that can be applied without knowing details  of the ASM formalism