ROLAP Servers: These are intermediate servers that sit between a relational back end server (where the data in
the warehouse is stored) and client front end tools. Microstrategy is an example of such servers. They
extend traditional relational servers with specialized middleware to efficiently support multidimensional
OLAP queries, and they typically optimize for specific back end relational servers. They identify the views that
are to be materialized, rephrase given user queries in terms of the appropriate materialized views, and generate
multi-statement SQL for the back end server. They also provide additional services such as scheduling of queries
and resource assignment (e.g., to prevent runaway queries). There has also been a trend to tune the ROLAP
servers for domain specific ROLAP tools. The main strength of ROLAP servers is that they exploit the
scalability and the transactional features of relational systems. However, intrinsic mismatches between
OLAP-style querying and SQL (e.g., lack of sequential
processing, column aggregation) can cause performance
bottlenecks for OLAP servers.