PPVL: The PIRL Parameter Value Logic The PIRL Parameter Value Logic is a tolerant C-Language application programmer interface (API) implementation of the Parameter Value Language (PVL). PVL is used as a standard in Planetary Data System (PDS) files to describe the information contained in the file (see http://pds.jpl.nasa.gov/stdref). It is a superset of the Object Description Language (ODL) that is used for describing information in other file formats; e.g. the HDF-EOS metadata attributes are described using ODL. Though the language specification is provided by the Consultative Committee for Space Data Systems in the Blue Book ("Parameter Value Language Specification (CCSDS0006)", May 1992 [CCSDS 640.1-B-1]) and Green Book ("Parameter Value Language - A Tutorial", May 1992 [CCSDS 640.1-G-1]) documents, various PDS products over the years have used PVL in different ways, some of which are now considered non-standard. The PPVL API has proven able to correctly interpret all PDS products it has encountered (e.g. viking, clementine, galileo, etc.) generated by various software systems (e.g. vicar, isis, etc.) and appears capable of handling any others. The PPVL API offers the ability to interpret, create, modify, and search PVL defined data structures as well as write PVL that conforms to the PDS standard. The implementation is available as a self-contained package on the PIRL anonymous ftp site (ftp://PIRLftp.LPL.Arizona.edu/pub/PPVL). Accessing the capabilities of the API is very easy. A useful little utility that resports on the PVL contents of a file is provided as an example application. An extension has been provided to make mapping of named PVL parameters to internal software variables a centrally managed table definition mechanism. This dramatically simplifies even complex uses of PVL files. The version of xv enhanced at PIRL to display PDS images is offered as a complete application of PPVL (also available from the PIRL anonymous ftp site: ftp://PIRLftp.LPL.Arizona.edu/pub/xv). The PPVL API, and the sample applications, have been built on various Unix flavors: Sun (SunOS, and Solaris), HP-UX, SGI/Irix, FreeBSD, and Linux, and porting to other operating environments should be trivial.