Ad-hoc data models like Json simplify schema evolution and enable multiplexing various data sources into a single stream. While useful when writing data, this flexibility makes Json harder to validate and query, forcing such tasks to rely on automated schema discovery techniques. Unfortunately, ambiguity in the schema design space forces existing schema discovery systems to make simplifying, data-independent assumptions about schema structure. When these assumptions are violated, most notably by APIs, the generated schemas are imprecise, creating numerous opportunities for false positives during validation. In this paper, we propose Jxplain, a Json schema discovery algorithm with heuristics that mitigate common forms of ambiguity. Although Jxplain is slightly slower than state of the art schema extractors, we show that it produces significantly more precise schemas.

We present Vizier, a multi-modal data exploration and debugging tool. The system supports a wide range of operations by seamlessly integrating Python, SQL, and automated data curation and debugging methods. Using Spark as an execution backend, Vizier handles large datasets in multiple formats. Ease-of-use is attained through integration of a notebook with a spreadsheet-style interface and with visualizations that guide and support the user in the loop. In addition, native support for provenance and versioning enable collaboration and uncertainty management. In this demonstration we will illustrate the diverse features of the system using several realistic data science tasks based on real data.