Bearing witness

A witness is someone who was there and says so under a duty to tell the truth, with perjury as the price of lying. Recordings, logs and model outputs are evidence, and increasingly good evidence, but they are exhibits; they do not swear, cannot be cross-examined about what they meant, and cannot be punished. Courts keep the oath for persons (US Federal Rule of Evidence 603, and its equivalents elsewhere) because testimony binds the one who gives it. Presence, memory and the willingness to be held to an account are what the act consists of.