John Caron

RESTful implementation of geospatial services for Earth and Space Science applications

Abstract In the recent years, Representational State Transfer (REST) has been proposed as the architectural style for the World Wide Web. REST promises of scalability and simple deployment of Web Services seem to be particularly appealing for Earth and Space Science (ESS) applications. In fact, most of the available solutions for geospatial data sharing, applying standard interoperability specifications, require complex service-oriented infrastructures; these are powerful and extensible environments, but they usually result in difficult to deploy and manage for ESS research teams. Thus, ESS researchers would gain great benefit from an easy way of sharing geo-information using the international interoperability standards. The variety and complexity of geo-information sharing services poses several architectural issues; in fact these services encompass sensor planning and observation, coverages and features publication and retrieving, models and simulations running, data citation and annotation. Consequently, the adoption of a specific architectural style must be carefully evaluated against these specific requirements. In this work we analyse the existing geospatial services from an architectural perspective and investigate their possible RESTful implementation. Particular attention is paid to the OGC Web Coverage Service (WCS). Possible benefits and drawbacks, along with open issues and possible solutions are discussed. Our investigation suggests that REST may fit well to the typical ESS research usage cases. However, the architectural choice (e.g. Simple Object Access Protocol (SOAP) vs REST) will depend on a case-by-case analysis. Other important factors must be considered, such as the application context: a valuable example in point are the e-Business and e-Government application scenarios which require message based solutions – like those implemented by SOAP. In any case, there is a clear need for harmonization and reconciliation of these two approaches.

Unidata’s Common Data Model mapping to the ISO 19123 Data Model

Access to real-time distributed Earth and Space Science (ESS) information is essential for enabling critical Decision Support Systems (DSS). Thus, data model interoperability between the ESS and DSS communities is a decisive achievement for enabling cyber-infrastructure which aims to serve important societal benefit areas. The ESS community is characterized by a certain heterogeneity, as far as data models are concerned. Recent spatial data infrastructures implement international standards for the data model in order to achieve interoperability and extensibility. This paper presents well-accepted ESS data models, introducing a unified data model called the Common Data Model (CDM). CDM mapping into the corresponding elements of the international standard coverage data model of ISO 19123 is presented and discussed at the abstract level. The mapping of CDM scientific data types to the ISO coverage model is a first step toward interoperability of data systems. This mapping will provide the abstract framework that can be used to unify subsequent efforts to define appropriate conventions along with explicit agreed-upon encoding forms for each data type. As a valuable case in point, the content mapping rules for CDM grid data are discussed addressing a significant example.

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.

Data access interoperability within IOOS

In this presentation we explore two efforts designed to promote interoperability between the OPeNDAP data access protocol and the OGC WFS and WCS protocols. The first is based on MapServer, an open-source development environment for building spatially-enabled Internet applications. Among other things, MapServer may be used as an OGC WFS and WCS server. As part of the effort described in this presentation the Simple Features Library (OGR) and the Geospatial Data Abstraction Library (GOAL) have been extended to support access to OPeNDAP enabled data sources. Because the OGR and GDAL libraries are core components of MapServer this extension enables OGC WFS and WCS access to OPeNDAP data sets. The second interoperability effort addressed is based on the THREDDS Data Server (TDS). The TDS is a new technology from Unidata, combining previous implementations of THREDDS Catalog Services with integrated data serving capabilities, including OPeNDAP and WCS. Because the TDS can operate as an OGC WCS server and as an OPeNDAP client it may be used as an OPeNDAP-WCS gateway. In both cases, metadata incompatibilities must be addressed. In the case of MapServer this is done via the OPeNDAP Ancillary Information Services capability, while in the TDS case it is done via routines that automatically convert metadata from some of the standards commonly used by OPeNDAP data providers, such as COARDS, to the metadata needs of WCS

NcML-G/sub ML/: encoding NetCDF datasets using GML

We describe the NcML-G/sub ML/: an extension of the NetCDF markup language (NcML). Such extension allows to encode NetCDF dataset resorting to GML 3.0 elements. It was conceived to facilitate the interoperability between the atmospheric science and the GIS communities; NcML-G/sub ML/ leverages the NcML effectiveness for encoding multidimensional arrays, encoding geo-metadata in GML. The abstract and the general content model which lead to the NcML-G/sub ML/are described.

An XML-based Language to Connect NetCDF and Geographic Communities

Geosciences and Geographic -information realms present several common aspects and share common data (i.e. they both generate, manage and use geospatial data). Nevertheless, they have been developing their own semantics, schemas and tools, which very often are not completely interoperable. That is the case of ncML (netCDF Markup Language) and GML (Geography Markup Language) content/semantics. Such issue is one of the main motivations for developing the presented ncML extension called ncML-GML. NcML-GML leverages the ncML ability to encode multi- dimensional arrays, and the wide acceptance of GML for encoding geospatial coverage. Based on GML 3.1.1 grammar, ncML-GML implements one of the possible encodings of a general interoperability model (i.e. both abstract and content interoperability models) which reconciles typical atmospheric sciences and geospatial data models. In this paper we describe the recently released version: ncML-GML ver. 0.7.3. The motivation, objectives and the newly-developed schemas are described and discussed. We also present the API (called N2G) developed to support ncML-GML documents as being used in the framework of GALEON IE - an OGC interoperability experiment which aims at extending the OGC WCS specification in order to support netCDF datasets. The role played by the ncML- GML in this experiment is presented and discussed.