BUILDING SERVICE-ORIENTED ARCHITECTURE BASED GEOSPATIAL WEB PORTAL

Geoscience research and applications often involve in analysis of a large volume of geospatial data. Traditionally, scientists spend a lot of time to install and learn a variety of software at local machines, search and collect the data from various data sources, preprocess and analyze the data at the local machines. This everything-locally-owned-and-operated paradigm makes the analysis and application of geospatial data very expensive and time-consuming. Recent advances in Service-Oriented Architecture (SOA) are shifting the geospatial data and analysis from the everything-locally-owned-and-operated paradigm to the everything-shared-over-the-Web paradigm (Web-and-Service-Centric paradigm). Currently, a significant number of geospatial datasets are available over the Web services, such as the Web Coverage Services (WCS) of OGC (Open Geospatial Consortium). These services perform various geospatial analysis functions. By embracing geospatial content and capabilities within the context of the SOA, we have developed a SOA-based geospatial Web portal, a fully extensible portal system for discovering, retrieving, analyzing and visualizing geospatial and other network data. The most distinguished characteristics of this portal is it is designed to use distributed software, hardware and applications to provide services from a number of different sources that enable 1) a single point of access to geospatial information and processes over the Web, 2) Web service-based analysis in which all functions are provided through interoperable Web services, and 3) user customization and collaboration by integrating and chaining user specific Web services.

The SOA uses loosely coupled and interoperable Web services to implement system requirements. All the services within the SOA are independent so that they can be accessed in a standard way without knowledge of how the service actually performs its tasks. Moreover, the SOA can support integration and orchestration of fine grained services into coarse grained composite services. The presented portal includes 4 main components: web portal, catalog service, data service and web processing service.

Web portal follows Model-View-Controller (MVC) design pattern to implement:

• User Portal: stores the current state of the portal in an OGC Web Map Context (WMC) document that can be imported again later to restore the portals state.

• Data Management: retrievals geospatial data from remote service and store them on the map server temporarily with a network accessible point.

• Data Analysis: selects or integrate a preferred processing service to do data analysis.

• Workflow: allows user to build a chain of services to perform the task.

• Data Visualization: sets up their own preference on how to display data, such as overlay sequence, data subsetting and image palette.

Data services provide users a common data environment to achieve the data interoperability. OGC WCS provides intact multi-dimensional and multi-temporal geospatial data as "coverage" to meet the requirements of client-side rendering, input of scientific models and other clients beyond simple viewers. OGC WFS (Web Feature Service) supports the networked interchange of geographical vector data as "feature" encoded in GML (Geographic Markup Language). OGC WMS (Web Map Service) provides geospatial data as "map" which is generally rendered in a spatially referenced pictorial image, such as PNG, GIF or JPEG, dynamically from real geographical data.

In distributed computing environment, a catalog service plays a ‘directory' role in helping the registration and discovery of data and services. The OGC Catalog Service for Web (CSW), an ebRIM (Electronic Business Registry Information Model) profile for Web-based geospatial catalog service, is implemented to enable register, discover and access to a wide variety of distributed geo-resources (i.e. geospatial data, applications, and services) through searching distributed catalog services, such as GEOSS (Global Earth Observation System of Systems) Clearinghouse, NASA ECHO (Earth Observing System Clearinghouse), and GeoBrain catalog. With regard to geospatial data metadata descriptions by ISO19115, the CSW makes some further extensions to accommodate the ISO model. The class “Dataset” is added into the ebRIM to provide a flexible way to describe a network accessible data offering. The CSW supports a variety of classification methods to enable service publisher to indicate the domain to which a service belongs at publication time, including OGC, ISO 19119 and NASA GCMD (Global Change Master Directory).

Web Processing Service (WPS) provides a domain specific computational model from simple spatial calculation to global climate change to enable users to do data analysis over network. For manipulating and analyzing vector and raster geospatial data, the portal itself provides more than 20 built-in WPSs and more than relevant 50 operations that are developed on top of GRASS (Geographic Resources Analysis Support System). The WPSs can also be chained together to perform more complex analysis task. Users can use these services to perform data analysis and data mining against any OGC-compliant online data sources. Moreover, the portal is able to be composed of Web services dynamically to provide user an open and fully extensible environment. If a user has his/her own geospatial processing services and would like to use them to do data analysis, he/she can integrate these services into the portal to build his/her own portal. If these services are registered into the catalog service, other portal users will benefit from them. Thereby, the more users involve, the more powerful the portal is.