Geospatial Web Services and Standards
Geospatial Web Services are Web-based geospatial applications that are modular, self-contained, and self-described with standard interfaces and thus support application-to-application interaction across different systems. Geospatial Web Services can be used to search for, access, and process geospatial data and information. The primary advantage of adopting Web Services is that they are standards-based and thus potentially fully interoperable among different applications and systems. There is a rich literature on Web Services and comprehensive reviews of Geospatial Web Services can be found (e.g., Zhao et al, 2007; Kralidis, 2007; Dietz, 2010). In addition to standards used in general Web Services such as the extensible markup language (XML) and the Simple Object Access Protocol (SOAP), most geospatial Web Services are developed using two suites of standards, namely those developed by the Technical Committee for Geographic information/Geomatics of the International Organization for Standardization (ISO/TC211) and those by the Open Geospatial Consortium (OGC). The TC/211 standards are mainly on the theoretical, conceptual, framework, or content levels, although some also specify implementation encodings such as ISO 19139:2007, which provides an XML schema implementation for TC/211’s metadata (ISO 19115:2003) and service standards (ISO 19119:2005). TC/211 standards “specify methods, tools and services for data management (including definitions and description), acquiring, processing, analyzing, accessing, presenting and transferring such data in digital/electronic form between different users, systems and locations.”1 OGC standards are focused on detailed protocols, interfaces, and encodings for geospatial Web Services so that “software developers use these documents to build support for the interfaces or encodings into their products and services.”2 Such implementable standards are called OGC implementation specifications and are developed based on OGC abstract specifications where the conceptual foundations are defined. The two standards bodies, ISO/TC211 and OGC, have collaborated closely in the past few years. Some OGC standards have been adopted by ISO/TC211 as international standards, such as the Web Map Service standard (as ISO 19128:2005) and Web Feature Service standard (now ISO 19142). Many geospatial Web Services have been developed and deployed in the past decade. The most relevant geospatial Web Service for EO data access is the Web Coverage Service because it deals primarily with data modeled as multi-dimensional arrays, which is the predominant EO data model.