Geonode notes

Stephen Richard edited this page Mar 6, 2014 · 12 revisions

pycsw and GeoNode Integration Notes

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Background

The OGC CSW 2.0.2 standard provides a discovery mechanism of geospatial metadata. For the HTTP protocol binding, the baseline information model is the Dublin Core (DC) Metadata Element Set. Additional profiles (such as APISO 1.0) exist to support specific information models (i.e. ISO 19115:2006) and output schemas (e.g. ISO19139:2007, OGC APISO, ISO EBRIM, ISO OWL).

Both ISO and DC allow for the advertisement of HTTP links. ISO's CI_OnlineResource construct allows for a certain level of granularity to express links (linkage, protocol, applicationProfile, name, description, function). For discussion of usage of this ISO metadata element, see this page at lab.usgin.org. Dublin Core defines a 'dct:references' [0..*] with the comment "A related resource that is referenced, cited, or otherwise pointed to by the described resource." This elements is typically used to encode URL's to get described resources in CSW record implementations. The csw:record XML implementation of the Dublin Core elements and terms allows any element to have a 'scheme' attribute of type xs:anyURI (see http://schemas.opengis.net/csw/2.0.2/rec-dcmes.xsd). There is no further granularity within dct:references.

Implementations have used dc:URI, however dc:URI is not actually defined as a Dublin Core element (its not standard).

A finer model is required to communicate different types of links (opaque, binding parameters, etc.). For an in depth discussion of Machine actionable Links, look here.

Motivation

Geonode, as a CSW client, requires the ability to identify various online linkages and be aware of their types/model to be able to process them accordingly (i.e. opaque, binding parameters, etc.).

This is possible given the ISO model, however it would be valuable to have an lightweight approach within DC that is inspired by ISO's CI_OnlineResource as well as fit within DC's dct:references element.

Proposal

Express ISO's CI_OnlineResource model in JSON using in dct:references/@scheme.

Example: <dct:references scheme="{'protocol': 'OGC:WMS-1.1.1-http-get-map', 'name': 'base%3Adistrits', 'description': 'distrits (JPEG Format)', 'linkage': 'http://localhost:8001/geoserver/wms'}">http://localhost:8001/geoserver/wms?layers=base%3Adistrits&width=620&bbox=-86.144%2C8.041%2C-82.555%2C11.221&service=WMS&format=image%2Fjpeg&srs=EPSG%3A4326&request=GetMap&height=550</dct:references>

Where:

  • dct:references.text: the full URL to the resource
  • dct:references/@scheme: a JSON representation of ISO's CI_OnlineResource:
  • name: the name of the link. In the case of an OWS, this should be the resource (layer|featureType|coverage) name
  • description: a human-readable description.
  • protocol: the type assigned to the URL, from the GeoNetwork gmd:online/gmd:CI_OnlineResource/gmd:protocol enumeration *
  • linkage: the URL of the resource. In the case of an OWS, this should be the service endpoint with query parameters

Alternate proposal.

The scheme attribute documentation in the rec-dcmes.xsd schema states "The scheme attribute may be used as a qualifier to reference an encoding scheme that describes the value domain for a given property.", it would be more consistent to make the JSON object in the dct:references element contain all the necessary information to understand the link. There are a number of proposals out there for JSON encoding of machine-actionable links (hypermedia profiles): HAL, SIREN, Hydra. The 'scheme' URI would identify which of these schemes was being used for the JSON in the dct:references element content. Multiple dct:references could be provided using different schemes. See examples in a fuller development of the proposal

Protocol enumeration and description

protocol description
ESRI:AIMS--http--configuration ArcIMS Map Service Configuration File (*.AXL)
ESRI:AIMS--http-get-feature ArcIMS Internet Feature Map Service
ESRI:AIMS--http-get-image ArcIMS Internet Image Map Service
GLG:KML-2.0-http-get-map Google Earth KML service (ver 2.0)
OGC:CSW OGC-CSW Catalogue Service for the Web
OGC:KML OGC-KML Keyhole Markup Language
OGC:GML OGC-GML Geography Markup Language
OGC:ODS OGC-ODS OpenLS Directory Service
OGC:OGS OGC-ODS OpenLS Gateway Service
OGC:OUS OGC-ODS OpenLS Utility Service
OGC:OPS OGC-ODS OpenLS Presentation Service
OGC:ORS OGC-ODS OpenLS Route Service
OGC:SOS OGC-SOS Sensor Observation Service
OGC:SPS OGC-SPS Sensor Planning Service
OGC:SAS OGC-SAS Sensor Alert Service
OGC:WCS OGC-WCS Web Coverage Service
OGC:WCS-1.1.0-http-get-capabilities OGC-WCS Web Coverage Service (ver 1.1.0)
OGC:WCTS OGC-WCTS Web Coordinate Transformation Service
OGC:WFS OGC-WFS Web Feature Service
OGC:WFS-1.0.0-http-get-capabilities OGC-WFS Web Feature Service (ver 1.0.0)
OGC:WFS-G OGC-WFS-G Gazzetteer Service
OGC:WMC-1.1.0-http-get-capabilities OGC-WMC Web Map Context (ver 1.1)
OGC:WMS OGC-WMS Web Map Service
OGC:WMS-1.1.1-http-get-capabilities OGC-WMS Capabilities service (ver 1.1.1)
OGC:WMS-1.3.0-http-get-capabilities OGC-WMS Capabilities service (ver 1.3.0)
OGC:WMS-1.1.1-http-get-map OGC Web Map Service (ver 1.1.1)
OGC:WMS-1.3.0-http-get-map OGC Web Map Service (ver 1.3.0)
OGC:SOS-1.0.0-http-get-observation OGC-SOS Get Observation (ver 1.0.0)
OGC:SOS-1.0.0-http-post-observation OGC-SOS Get Observation (POST) (ver 1.0.0)
OGC:WNS OGC-WNS Web Notification Service
OGC:WPS OGC-WPS Web Processing Service
WWW:DOWNLOAD-1.0-ftp--download File for download through FTP
WWW:DOWNLOAD-1.0-http--download File for download
FILE:GEO GIS file
FILE:RASTER GIS RASTER file
WWW:LINK-1.0-http--ical iCalendar (URL)
WWW:LINK-1.0-http--link Web address (URL)
WWW:LINK-1.0-http--partners Partner web address (URL)
WWW:LINK-1.0-http--related Related link (URL)
WWW:LINK-1.0-http--rss RSS News feed (URL)
WWW:LINK-1.0-http--samples Showcase product (URL)
DB:POSTGIS PostGIS database table
DB:ORACLE ORACLE database table
WWW:LINK-1.0-http--opendap OPeNDAP URL
RBNB:DATATURBINE Data Turbine
UKST Unknown Service Type

Extensions to protocol enumerations and descriptions

protocol description
WWW:LINK-1.0-http--image-thumbnail Web image thumbnail (URL)

Examples

WMS Layer with only binding information <dct:references scheme="{'protocol': 'OGC:WMS-1.1.1-http-get-map', 'name': 'base%3Adistrits', 'description': 'distrits (JPEG Format)', 'linkage': 'http://localhost:8001/geoserver/wms'}">http://localhost:8001/geoserver/wms?layers=base%3Adistrits&width=620&bbox=-86.144%2C8.041%2C-82.555%2C11.221&service=WMS&format=image%2Fjpeg&srs=EPSG%3A4326&request=GetMap&height=550</dct:references>

Thumbnail <dct:references scheme="{'protocol': 'WWW:LINK-1.0-http--image-thumbnail', 'name': 'base%3Adistrits', 'description': 'Web image thumbnail (URL)', 'linkage': 'http://localhost:8001/geoserver/wms'}">http://localhost:8001/geoserver/wms?layers=base%3Adistrits&width=20&bbox=-86.144%2C8.041%2C-82.555%2C11.221&service=WMS&format=image%2Fjpeg&srs=EPSG%3A4326&request=GetMap&height=20</dct:references>

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