Tool support for data validation by end-user programmers

End-user programming tools for creating spreadsheets and webforms offer no data types except "string" for storing many kinds of data, such as person names and street addresses. Consequently, these tools cannot automatically validate these data. To address this problem, we have developed a new userextensible model for string-like data. Each "tope" in this model is a user-defined abstraction that guides the interpretation of strings as a particular kind of data, such as a mailing address. Specifically, each tope implementation contains software functions for recognizing and reformatting that tope\´s kind of data. With our tools, end-user programmers define new topes and associate them with fields in spreadsheets, webforms, and other programs. This makes it possible at runtime to distinguish between invalid data, valid data, and questionable data that could be valid or invalid. Once identified, questionable and/or invalid data can be double-checked and possibly corrected, thereby increasing the overall reliability of the data.