Data repositories often consist of text files in a wide variety of standard formats, ad-hoc formats, as well as mixtures of formats where data in one format is embedded into a different format. It is therefore a significant challenge to parse these files into a structured tabular form, which is important to enable any downstream data processing.

We present \textsc{Unravel}, an extensible framework for structure interpretation of ad-hoc formats. \textsc{Unravel} can automatically, with no user input, extract tabular data from a diverse range of standard, ad-hoc and mixed format files. The framework is also easily extensible to add support for previously unseen formats, and also supports interactivity from the user in terms of examples to guide the system when specialized data extraction is desired. Our key insight is to allow arbitrary combination of extraction and parsing techniques through a concept called \emph{partial structures}. Partial structures act as a common language through which the file structure can be shared and refined by different techniques. This makes \textsc{Unravel} more powerful than applying the individual techniques in parallel or sequentially. Further, with this rule-based extensible approach, we introduce the novel notion of \emph{re-interpretation} where the variety of techniques supported by our system can be exploited to improve accuracy while optimizing for particular quality measures or restricted environments. On our benchmark of $617$ text files gathered from a variety of sources, \textsc{Unravel} is able to extract the intended table in many more cases compared to state-of-the-art techniques.