For the entities in the file family (see Figure 4), there are short cuts on some column headers for the corresponding file list. The second way of query is simple to use: just open the query box on the corresponding header, select the operations and input the value to be queried. It is simplified because it does not allow building complex query expression and if more than one column query box have non-empty value, they are all “AND” jointed.
There is a text based query expression editor for very entity set inside the virtual database (namely the ones corresponding to the 61 virtual tables). The query expression editor can be used to build arbitrarily complex query expressions. The said editor is backed by a sub-SQL DSL generator that can guide the user to construct expressions without been too smart (namely make decisions for the user). Most of the input inside the query expression editor can be accomplished by using four keys, namely the right, up and down arrow keys and the back delete key to select or delete. The expression constructed can be saved and recalled later to re-used or edited.
The future version of the system will contain a graphic expression “designer” using which a user can use mouse (or touch finger) to drag, group and choose logic operators to construct equally complex filter predict expressions as in b).