NOcontaining

NOcontaining is a term used in data validation and content filtering to describe a constraint that a string must not contain any items from a specified set of forbidden substrings or characters. Formally, given a finite dictionary F of forbidden patterns, the allowed language L consists of all strings over an alphabet Σ that do not contain any f in F as a contiguous substring. The concept is widely applied in practices where controlling content or leakage is important.

Implementation approaches include automata-based and pattern-based methods. Aho-Corasick automata can detect multiple forbidden substrings in linear time, making NOcontaining suitable for real-time filtering. Regular expressions with negative lookahead or streaming filters can also enforce the constraint, though performance and maintainability depend on the size of F and the encoding used. For dynamic sets F, update mechanisms and efficient data structures help maintain timely enforcement.

Applications span multiple domains. Content moderation uses NOcontaining to block profanity or disallowed terms; data loss prevention employs it to prevent exfiltration of sensitive keywords; input sanitization helps avoid injection attacks by forbidding risky substrings. It can also constrain text-generation outputs or templating systems to avoid leaking placeholders or confidential terms.

Limitations include the risk of overblocking, where legitimate content is inadvertently blocked, and the potential for inefficiency with very large or frequently changing forbidden sets. Proper tuning of F, consideration of case sensitivity, and handling of internationalized text are important for reliable NOcontaining enforcement. Related concepts include forbidden-substring constraints and content-filtering pipelines.