1. A computing system for specifying one or more validation rules for validating data included in one or more fields of each element of a plurality of elements of a dataset, the computing system including: a user interface module configured to render a plurality of cells arranged in a two-dimensional grid having a first axis and a second axis, the two-dimensional grid including one or more subsets of the cells extending in a direction along the first axis of the two-dimensional grid, each subset of the one or more subsets associated with a respective field of an element of the plurality of elements of the dataset, and multiple subsets of the cells extending in a direction along the second axis of the two-dimensional grid, one or more of the multiple subsets associated with a respective validation rule; a subset of the cells extending in a direction along the second axis of the two-dimensional grids, each cell in the subset being associated with the respective field at the corresponding position in the grid identified by the second axis, and being capable of being used as a conditional cell, and wherein a condition cell associated with a field includes an input element, for receiving input in the form of a conditional expression; and a processing module configured to evaluate a conditional expression from a condition cell and, based on that evaluation, apply one or more validation rules to at least one element of the dataset.