Filters are a very important part of the querying process, helping to refine requests, filter unneeded information, and reduce system resource consumption to manageable levels. One way to further increase the reach of filters in a managed query environment is to think of them in terms of both the query and the underlying Data Model, and of ways in which fixed and variable filters may be used together.
Fixed filter values are defined with a query, and remain static until changed manually. Variable filters prompt for new values each time a query is processed. In certain instances you may want to apply both types of filter to one item in order to restrict the available variable filter values and simplify users' choices, or to grant users the latitude of variable filters only within a prescribed range.
For example, consider users of a large data warehouse or legacy system containing sales data going back for many years. For practical or security reasons the administrator might choose to confine some users' access to information dating after 1990. However, it is still important for these users to query the database on-the-fly, and retrieve a variety of data for analysis.
This situation requires two filters, one fixed and one variable, on one topic item. The fixed filter qualifies the values set available to the user in the variable filter. The fixed filter on a date column item instructs the server not to return any values < 1/1/90. The variable filter on the same date column subsequently furnishes a list of server values > 12/31/89 for the user to choose when the Showing Values command is invoked in Filter Controls.