Support to Distributed Search

8 interconnected graph, a search is conducted from current catalogue to the sub-catalogs that connect with it. Setting a maxLevel to 2 will allow the search of sub-catalogs that directly link to the current catalog, or those that are two steps further from the current catalog. In another words, they are the catalogs that link with the direct sub-catalogs of the current catalog. Setting a maxLevel to -1 will enable a search for all sub-catalogues from the current level. Using the parameter maxLevel, the query scope can be controlled. In CSW 2.0.2, potential problems of distributed catalog search are also discussed and described. In Annex B of the standard, two problematic scenarios are defined. The first problem is when one node X has two parent nodes. In this case, when a search is conducted, i.e., from a node that is the precedent of both the parent nodes, the node X will be searched twice, causing duplication in the result. The second problem is caused by a complex topology of the catalog network. For example, when catalog Y is linked to catalog Z, which is its precedent, catalog Z becomes Y’s child node too. In this case, a loop is formed, whereby a search that redirects to Z will fall in a repeated search between Y and Z causing serious issues. Although these problems are discussed, this version of specification did not describe how to solve these problems by extending the definition of the CSW information model.

6.1.4 Usability

The CSW 2.0.2 standard has been widely used in national and international spatial data infrastructure projects. Below we list a sample set of CSW endpoints that were discovered by the NSF PolarHub, a large-scale web crawler for discovering distributed OGC services Li et al. 2015: CSW Catalogs URL United States Geoscience Information Network Metadata Catalog http:catalog.usgin.orggeoportalcsw?request=GetCapabilitie sservice=csw GEOSS CSR Catalog http:geossregistries.infogeonetworksrvencsw?Request=Ge tCapabilitiesService=CSWVersion=2.0.2 ArcGIS Server Geoportal Extension 10 - OGC CSW 2.0.2 ISO AP http:catalog.chesapeakebay.netgeoportalcsw?Request=Get CapabilitiesService=CSWVersion=2.0.2 ArcGIS Online CSW Interface http:geoss.esri.comcswcsw?request=GetCapabilitiesservi ce=CSWversion=2.0.2 ArcGIS Server Geoportal Extension 10 - OGC CSW 2.0.2 ISO AP http:portal.westcoastoceans.orggeoportalcsw?request=GetC apabilitiesservice=CSWversion=2.0.2 Servicio de catalogación OGC CSW de IDECA http:metadatos.ideca.gov.cogeoportalcsw?request=GetCapa bilitiesservice=CSW ArcGIS Server Geoportal Extension http:data.nconemap.comgeoportalcswdiscovery?request=G 9 10 - OGC CSW 2.0.2 ISO AP etCapabilitiesservice=CSWversion=2.0.2 IARC Data Archive CSW Service http:climate.iarc.uaf.edugeonetworksrvcsw?REQUEST=G etCapabilitiesSERVICE=CSWVERSION=2.0.2 CSW Geospatial Catalogue for NOAA Data Catalog data.noaa.gov https:data.noaa.govcsw?request=GetCapabilitiesservice=C SWversion=2.0.2 Welsh Government INSPIRE CSW http:inspire.wales.gov.ukmetadatasrvengcsw?REQUEST= GetCapabilitiesservice=CSWversion=2.0.2 geocat.ch http:www.geocat.chgeonetworksrvengcsw?REQUEST=G etCapabilitiesSERVICE=CSWVERSION=2.0.2 UK Location Catalogue Publishing Service http:csw.data.gov.ukgeonetworksrvcsw?REQUEST=GetC apabilitiesSERVICE=CSWVERSION=2.0.2 Copeland Borough Council GeoPortal Discovery Service http:gistch1.copelandbc.org.ukgeonetworksrvcsw?REQUE ST=GetCapabilitiesSERVICE=CSWVERSION=2.0.2 Catalogue Service Land Steiermark Geoportal Server 1.2.2 - OGC CSW 2.0.2 ISO API including INSPIRE Network Service Capabilities http:gis.stmk.gv.atgeoportalcswdiscovery?Request=GetCa pabilitiesService=CSWVersion=2.0.2 geocat.ch http:www.geocat.chgeonetworksrvengcsw?REQUEST=G etCapabilitiesSERVICE=CSWVERSION=2.0.2 geonetwork GRID http:129.194.231.213:8080geonetworksrvcsw?REQUEST =GetCapabilitiesSERVICE=CSWVERSION=2.0.2 North Dakota GIS Hub Data Portal httpshttp:apps.nd.govhubdataportalsrvencsw?REQUEST=GetCa pabilitiesservice=CSWversion=2.0.2 VLIZ Geonetwork http:geonetwork.vliz.begeonetworksrvencsw?request=Get Capabilitiesservice=CSW Table 1. A list of sample CSW 2.0.2 endpoints

6.2 CSW 3.0

6.2.1 Introduction

The OGC Catalogue Services 3.0 Standards Working Group OGC CSW 3.0 SWG for short, initiated in March 2008, aimed at developing a new version of the standard to advance existing CSW 2.0.2 definitions for catalog management and search. The new standard CSW 3.0, published on March 18, 2014, was edited by Lorenzo Bigagli, Doug Nebert, Uwe Voges, Panagiotis Vretanos, and Bruce Westcott. The main areas of enhancement in CSW3.0 with regard to CSW 2.0.2 include: