Abstract: A just-in-time sampling-based system can, after consuming a small number of disk accesses or queries, produce extremely accurate answers for a broad class of aggregate and top-k queries over a file system or database without the requirement of prior knowledge. The system is efficient, accurate, and scalable. The system performs aggregate estimations of a hidden database through its web interface by employing techniques that use a small number of queries to produce unbiased estimates with small variance. It conducts domain discovery over a hidden database through its web interface by employing techniques which provide effective guarantees on the effectiveness of domain discovery. Systems and methods enhance forms used by mobile devices to access hidden databases. It employs data analytics to improve the usage of form fields, including providing context-sensitive auto-completion suggestions, highlighting selections in drop-down boxes and eliminating suggestions in drop-down boxes.