OGC Interoperability Day at Unidata:
Standards-based Web Services Interfaces to
Draft by Ben Domenico
Last Updated: September 16, 2009
The agenda has gotten packed with presentations on important topics relating to the use of standard interfaces (CS-W/ebRIM, WFS, WCS, SOS, GML) for providing access to data currently served via THREDDS, OPeNDAP, netCDF-CF and IDD/LDM technologies. These packages are in widespread use in the community sometimes referred to as Fluid Earth Sciences (FES) and deliver large collections of weather, climate and ocean data.
An effort has been made to shorten the presentations and combine topics in order to leave a modicum of time for informal interactions during breaks and over lunch. In addition there are provisions for participants to set up demonstrations in the lobby area to foster discussions during the breaks.
The overall objective is to come up with practical and concrete ideas for how to provide the functionality of the existing THREDDS, OPeNDAP, netCDF-CF and IDD/LDM technologies for the various classes of FES datasets -- but to do so through standard interfaces so that other communities such as the traditional GIS community can have ready access to the FES datasets. The primary focus will be on gridded datasets (e.g., weather forecast model output) and station/observation/point datasets (e.g. the observational data collected at weather stations, ocean buoys, river gaging stations). Other categories (profile/trajectory, swath, radial, unstructured grids) will be addressed if there is time. The idea is that, if we can come up with a plan for dealing with gridded and station/observation/point datasets, we can incrementally work on the other categories using what we have learned from the first two.
One important outcome will be a list of services and client tools that are already availabel for use and testing. In addition, we'd like to come away from the session with commitments from participants for practical implementations they will make available in the next six months to a year, so that others can coordinate their own efforts at implementation and testing of the components for which they have special expertise and experience.
An effort has been made to expand the time available for informal discussions during lunch and breaks. Also, tables will be available in the Center Green main lobby where participants can set up demonstrations of their systems to facilitate the informal discussions.
Some possible ways in which participants might contribute are:
Presumably many more ideas will arise during the Interoperability Day discussions, but this list will hopefully get participants thinking along the lines of possible contributions.
The sessions will be webcast at:
The presentations will be posted on the GALEON wiki at:
Arliss Whiteside has drafted a very useful concise overview of several key OGC Web Services: WMS, WCS, WFS, CS-W. We are making a copy available at:
The THREDDS Data Server (TDS) is a web server that provides metadata and data access for scientific datasets, building on existing technologies and protocols.
This document describes a Convention for NetCDF (version 3) files for writing Point, Trajectory, Profile, and Station observation data
This document provides an overview and status update on the OGC GALEON (Geo-interface for Air Land Environment Oceans NetCDF) Interoperability Experiment.
The primary goal of the OGC GALEON interoperability experiment is to provide a standards-based interface to the wealth of Earth science datasets that are currently available in netCDF and HDF form -- often served via the OPeNDAP client-server protocol. This document describes the underlying data models used in those technologies. In particular it focuses on the Unidata Common Data Model (CDM) which combines the most valuable features of netCDF (augemented with CF conventions), HDF, and OPeNDAP and maps that into the corresponding elements of the international standard ISO 19123 -- specifically for the Discrete Grid Point Coverage data model.
One approach that provides alternative standards-based interfaces to the underlying data is to build on the WCS servers established in GALEON Phase 1. Then chain alternative interfaces such as WFS or SOS such that a wide variety of clients representing different user comunities can access the same data via a familiar service interface. All these data resources and interfaces can be cataloged using the CS-W interface. This allows each group to work on their own components within the realm of their primary expertise, but always keeping the work of the others in mind. In the end the goal would be to minimize the tendency for the protocols and encodings to drift apart.
At the Fall 2006 AGU meeting, Andrew Woolf presented ‘Feature types’ as an integration bridge in the climate sciences*. Andrew's presentation can be viewed as a top-down view of a problem we have been approached from the bottom up in THREDDS and to some extent in GALEON. One might also say that end users and client developers look at data in terms of 'feature types' whereas data providers are confronted with 'collections of files." In point of fact, the GALEON project is stuck right in the middle of these two "data world views." If we are to design and implement interfaces that effectively and intuitively connect user's client applications with the collections of files that exist at data provider sites, it is important to have a clear understanding of both complementary perspectives. This document is an attempt to incorporate the information and diagrams from Andrew's presentation and relate it the GALEON to provide standard interfaces to the vast collections of data available on THREDDS Data Servers (TDS).