ASN.1 was great. Another old specification language still in use today is EXPRESS, one of the foundations of the huge ISO 10303 (STEP) standard series, as defin

ASN.1 was great. Another old specification language still in use today is EXPRESS, one of the foundations of the huge ISO 10303 (STEP) standard series, as defined in ISO 10303-11. It even has algebraic data types. The development of STEP started in 1984 and has been one of the largest efforts ever undertaken by ISO.