Multi-platform implementation approach Foundation concepts

flow control are examples of transactions that can be more difficult as each tier may run on different operating systems, be written in multiple software languages, and communicate using several protocols. Technology-specific enterprise frameworks have been developed to address some of these challenges. Examples of these enterprise frameworks include J2EE or .NET, which address interoperability challenges of distributed computing by constraining options more narrowly around specific enterprise technologies. For example, J2EE is built around java-based technologies and .NET around Microsoft Windows. The goal of OGC-based architectures is to provide interoperability beyond the technology viewpoint. This goal is accomplished by defining higher-level interface specifications that are independent of individual technical implementations. This approach helps meet the NSG’s common vision for Geospatial Intelligence see: Geospatial Intelligence Standards: Enabling a Common Vision http:www.nga.milNGASiteContentStaticFilesOCRncgis-eb.pdf. Distributed n-tier architectures have to address interoperability across tiers independent of technology if goals such as technology risk reduction, improved choice and competition in the marketplace, reduced technology costs, and the ability to rapidly insert new technology are to be achieved, Ibid p.13. In an earlier OpenGIS® best practices paper OpenGIS® web services architecture description OGC 05-042r2, OGC has set out a web services architecture around OGC interfaces. This n-tier architecture shown in figure TBD defines three services types or components loosely arranged in four tiers, from Clients to Application Services to Processing Services to Information Management Services but un-needed tiers can be bypassed. This Service Oriented Architecture is based on the fundamental roles of service provider and service consumer within a distributed computing system. This pattern emphasizes that desired computing can be realized by combining multiple services, for each of which only the service types e.g., interfaces and abilities and server data holdings e.g. content need be known. It focuses component definition on providing andor consuming a defined service. 12 Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. Figure 6 - Service tiers in OWS Architecture As shown n the OWS Architecture service components are organized into multiple tiers. 1. All components provide services, to clients andor other components, and each component is usually called a service with multiple implementations or a server each implementation. 2. Services or components are loosely arranged in four tiers, from Clients to Application Services to Processing Services to Information Management Services, but un-needed tiers can be bypassed. 3. Services can use other services within the same tier, and this is common in the Processing Services tier. 4. Each tier of services has a general purpose, which is independent of geographic data and services. 5. Each tier of services includes multiple specific types of services, many of which are tailored to geographic data and services. Information Management Services Tier The Information Management Services tier contains services designed to store and provide access to data, with each server normally handling multiple separate datasets. In addition, metadata describing multiple datasets can be stored and searched. Access is usually to retrieve a client-specified subset of a stored dataset, or to retrieve selected metadata for all datasets whose metadata meets client-specified query constraints. OGC 05-042r2 p 14. Examples of Information Management Services include: Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 13