Nquery is a Java-based, network-enabled data-based query tool that loads pertinent subsets of multi-disciplinary, earth-science datasets into a temporary, on-the-fly relational database, performs local calculations, and then allow a scientist to construct sophisticated SQL queries. What distinguishes Nquery from other data selection tools is the ability to find a subset of a dataset from the values of measured parameters rather than just the spatial domain.

Nquery computes summary statistics (e.g., average value, depth of maximum value, and depth of minimum value) for a profile or time series from the observed parameters and from user-specified calculations (e.g., mixed-layer depth, apparent oxygen utilization, and interpolation of a measured parameter to a standard level). A simple two-step process takes the user from pre-selected data (e.g., from Climate Data Portal, EPIC Web, or Dapper/OPeNDAP) to a set of data files selected from the computed summary statistics. First, the user determines what observed and computed variables will be used to construct the database, and therefore are available for subsequent queries. This selection is accomplished via a simple graphical interface that lists all available variables. Additional dialogs allow selection and configuration of a large set of computed variables. A single click then begins the process of ingesting the data files, computing summary statistics for both the observed values and user-specified calculated values, and building and populating the MySQL database. Second, after the database has been populated with the requested data, the user can create a SQL query using a second graphical user interface.

The user can build simple to fairly complex queries by using either the graphical interface, or entering an SQL statement by hand. Once a satisfactory query is constructed, it is executed by the database, resulting in a list of files that satisfies the query. The scientist can then use these files in other research tools by exporting a “pointer file” that contains the location of the actual data file.