Some businesses today are investing in a simple data warehousing tool that provides end users with direct access to operational data on legacy databases, commonly known as a virtual data warehouse. In this ‘virtual’ scenario, data is not moved from source databases to a target data warehouse as in a traditional data warehouse scenario. In fact, a target database and data warehouse do not exist within a virtual environment. Instead, users utlilize intuitive end-user tools to access data directly from operational files, using common business terms.

The virtual data warehouse is popular because it enables businesses to access and analyze data from operational systems, such as Oracle Financials or SAP R/3, without having to rely on IT personnel to extract and process the data. Virtual data warehouses utilize existing legacy systems as database servers and require minimal investment in additional hardware and software.

The advantage of virtual data warehousing is its simplicity. There is no need for complex data extraction and transformation tools, metadata repositories or separate data warehouse databases. The ability to access data directly from legacy systems with intuitive front-end data warehousing tools preserves a business’ investment in mainframe hardware, software, databases and skillsets.

However, the primary limitation of a virtual data warehouse is that it is not a true data warehousing environment. A virtual data warehouses does not include a data warehouse database, contains no historical data, has little summarization or aggregation of data, does not have central metadata, and does not have the ability to cleanse and reorganize data. Furthermore, since query functions access data directly from source files, on-line operations are likely to be disrupted. Query functions such as “Show me the inventory level, sell through, and turnover for my ten highest and lowest selling items” can result in a massive number of query functions that can severely impact the operational performance of host computers that drive the business.

Although virtual data warehouses may save money initially, they will have to be re-implemented on a dedicated, physically separate data warehousing facility at some time in the future. Moreover, moving from a virtual data warehouse to a dedicated warehouse may be extremely disruptive if it occurs at a time when the data warehouse is required to support a large number of business end users. If an organization does decide to build a virtual data warehouse to support direct access to operational data, these “warehouses” should be considered temporary facilities, and will eventually need to be replaced with a true data warehouse.