Are Standards an Ambiguity-Free Reference for Product Validation?

The increased use of standards as references for safety-critical applications is drawing the attention of researchers on the fact that the responsibility for the safety of standard-compliant systems may depend not only on developers and assessors, but also on the standards themselves. This paper is focused particularly on some quality aspects of standard clauses, i.e., the natural language statements that are expressed by the standards, and to which a standard-compliant process or product is required to adhere. Various railway standards are considered, and some linguistic issues, potentially leading to ambiguity of clause interpretation, are discovered with the aid of natural language processing (NLP) tools. Real cases of problems in clause interpretation, taken from industrial experience, are reported, to show the possible impact in products and processes that must be validated against such clauses, and to justify the importance of the analysis.