GALEON: Standards-based web services for interoperability among Earth sciences data systems

One barrier to research at the boundaries of the traditional Earth sciences is a lack of interoperability among data systems employed in the traditional subdisciplines. Solid Earth scientists (including the hydrology community) have tended to view their datasets as descriptions of discrete objects with attributes that can be stored and manipulated conveniently in a database. Geographic Information Systems (GIS) work well in this environment. On the other hand, the oceanographic and atmospheric sciences (the Fluid Earth Sciences or FES) communities think of data as discrete points in a continuous mathematical function space where the behavior of multiple parameters in space and time is governed by a set of equations. In an attempt to bridge the gap between these groups, the GALEON (Geo-interface for Air, Land, Earth, Ocean NetCDF) interoperability experiment is being conducted under the aegis of the Open Geospatial Consortium (OGC). There are two main components of this initiative: A Formal OGC Interoperability Experiment. The objective is to ascertain the suitability of the OGC Web Coverage Service (WCS) interface specification for serving datasets that are typical of those stored in netCDF (network Common Data Form). This will be done in the context of the formal OGC interoperability experiment. About a dozen WCS client and server implementations are involved in this aspect of the experiment. A few of these existed before GALEON; others are being developed in conjunction with the experiment. A WCS Gateway Implementation. The second component is to develop WCS client and server software implementations that will enable the WCS clients to access data via a WCS gateway to existing distributed servers that already serve data in netCDF. This will be done by the netCDF, THREDDS (THematic Real-time Environmental Distributed Data Services), OPeNDAP (Open Project for a Network Data Access Protocol, formerly the Distributed Oceanographic Data System, DODS), LAS (Live Access Server), GDS (GrADS Data Server formerly GrADS Data Server), etc. The primary objectives of formal OGC interoperability experiment are to determine whether: 1. a viable WCS getCapabilities geo-interface (gateway in earlier versions) can be built on existing THREDDS inventory catalog services 2. the ncML-G data model is adequate for providing describeCoverage responses for netCDF datasets 3. there are any solutions to the previously identified limitations to geoTIFF encoding format for representing 5-D netCDF files in such a way that the relationships among layers are preserved 4. the proposed ncML-GML encoding format is a practical solution to serving 5D data from netCDF files, either embedded (ASCII or attached binary) or linked (OPeNDAP link or other URL) 5. netCDF itself is a viable WCS binary encoding format 6. existing WCS clients are able to access analyze and display 5D data from netCDF files 7. 5D geospatial data sets can be served efficiently through standard database technology In essence, the second GALEON component is to specify and implement a web services interface to traditional atmospheric and oceanographic datasets currently stored in netCDF form or served via the OPeNDAP protocol. The project uses the OGC WCS interface specification to provide access to datasets currently available via a combination of technologies including THREDDS and HDF5 (Hierarchical Data Format) in addition to netCDF and OPeNDAP. An important aspect of the experiment is to test the adequacy of the Geography Markup Language (GML) for representing the information contained in netCDF files and associated community "conventions." One approach to this is based on transformation of coordinate system extensions to NcML (netCDF Markup Language) into GML (Geography Markup Language) extensions to NcML. These extensions, called NcML-GML form a subset profile of the full GML which is in the late stages of adoption by the ISO (the International Standards Organization). A second dialect of GML, called Climate Systems Modeling Language (CSML) is also under development by another of the GALEON participants. In all, the participants in GALEON represent a wide range of private sector companies, government agencies, and academic institutions from around the globe. The paper presents the current status for each actively participating organization along with updated objectives of the GALEON team.