GeoNetwork opensource implements both the Portal component and the Catalog database of a Spatial Data Infrastructure (SDI) defined in the OGC Reference Architecture. It provides tools for managing and publishing metadata on spatial data and related services. GeoNetwork opensource allows a distributed search providing access to a huge volume of metadata that come from different Clearinghouses and also provides a web-based interactive map viewer that allows people to composite maps picking layers from distributed servers on the internet.

In more detail, GeoNetwork opensource, like the OGC Reference Architecture, employs:

• Portal Services that provide the access to the geospatial information as well as the management and administration of the portal and users. A set of rules allows Authentication and Access Control that regulate, through controlled privileges, the access to reserved information and services. In addition, the Portal Platform offers an Advanced Metadata Editor Module that is able to create and edit ISO compliant metadata records for geographic data using the Standard ISO 19115. The map viewer, part of the portal services, is provided by InterMap, another joint FAO-WFP opensource project (http://sourceforge.org/projects/intermap). Intermap allows the user to select map layers from several servers, overlay them and create a customized composite map. It can use the WMS protocol to talk to OGC servers and can interact with ESRI-based servers using the ArcIMS protocol. Intermap provides support for access to temporal web map services (like time-series of satellite data) and WMServices that provide different types of symbology (SLD). Finally, InterMap offers metadata support allowing linking back to a data description once the layer has been displayed on the web.
•    Catalog Services that allow the collection, registration and maintenance of descriptive information about the data stored in the database. The Catalog Services implements a Metadata Clearinghouse which includes a facility to retrieve all the information on the spatial data made available by other Clearinghouses. More precisely, the OGC Web Catalog services Z3950 protocol allow distributed search capabilities, i.e. GeoNetwork opensource can access other databases and vice versa, taking into account security settings on metadata and data.
•    Data Services components that are being implemented by GeoNetwork opensource to complete the OpenGIS Framework of the Reference Architecture. This particular class of services provides access to spatial content in repositories and databases and allow data processing through defined common encodings and interfaces. Furthermore the Data Services can be distributed across the Internet thus they don`t need to be resident on the operational portal.

GeoNetwork opensource does not directly provide the Map Portrayal, the fourth component of the OGC Reference Architecture, which makes possible the visualization on the Internet of geospatial information. However, several open source projects exist which implements the Map Portrayal component that can be integrated with the GeoNetwork opensource package; for instance Deegree, MapServer and GeoServer. GeoNetwork opensource version 1 has been available with an embedded Deegree server, providing all components of the OGC Reference Architecture as an integrated package. This effort has been improved recently joining the OpenSDI group, which has the purpose of aiding the integration of different OCG Reference Architecture components; the GeoNetwork opensource team is working closely with that group to support seamless integration of GeoNetwork opensource with these and other projects implementing OGC standards.

Figure 1. Geospatial Portal Reference Architecture