ASDeX is an abbreviation of a formal specification language: Analog Specification Description in XML. It is defined with the help of XML-Schema-Definition (XSD). An ASDeX-file contains not only specification parameters but also measurement definitions and testbenches to enable specification validation based on simulation. An ASDeX-file could be used as a starting point in a top-down design flow as well as a final sign-off point after circuit design controlling e.g. characterization and property validation. ASDeX or eventually a striped version of it could also be used as an exchange format for analog IP description in the sense of IP-XACT. Currently, ASDeX is used in an automatic specification driven validation flow. Further work will focus on the investigation of hierarchical specifications for analog/mixed-signal (AMS) System, the extension for handling temporal logic, and the integration into a synthesis design flow, e.g. a topology synthesis method of analog circuits.