Online Resource Documentation

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Overview

As the World Wide Web has developed into a ubiquitous information source, links to on-line information and services have become critical elements in all metadata dialects. Some dialects emerged during the early days of the web when less was known about how it would develop and flourish. URLs were simple and self-explanatory and it was enough to include just the bare URL in the metadata. As URLs have increased in complexity, it has become more important to provide supporting information along with the links.

Implementation

Content Standard for Digital Geospatial Metadata (CSDGM)

Structure

Directory Interchange Format (DIF)

Structure

URL's are described in DIF using the Related_URL field. They have the following properties:

<dif:Related_URL uuid="UUID">
    <dif:URL_Content_Type/>
    <dif:URL/>
    <dif:Description/>
</dif:Related_URL>

The URL_Content_Type field comes from the URL Content Type URL Content Type List which provide standard names for a number of data systems and services. Data access URLs can be recognized by the URL_Content_Type = "GET DATA". The Related_URL field is highly recommended and may be repeated.

EOS Clearinghouse (ECHO)

Structure

The ECHO model includes several types of URLs, each with a unique set of properties:

<OnlineAccessURL>
    <URL/>
    <URLDescription/>
    <MimeType/>
</OnlineAccessURL>

<OnlineResource>
    <URL/>
    <Description/>
    <Type/>
    <MimeType/>
</OnlineResource>

<ProviderBrowseUrl>
    <URL/>
    <FileSize/>
    <Description/>
    <MimeType/>
</ProviderBrowseUrl>

International Organization for Standardization 19115 (ISO19115)

Structure

The ISO Standards use CI_OnlineResources to describe links. They include the following properties:

<gmd:CI_OnlineResource>
    <gmd:linkage/>
    <gmd:protocol/>
    <gmd:applicationProfile/>
    <gmd:name/>
    <gmd:description/>
    <gmd:function/>
</gmd:CI_OnlineResource>

Usage

Usage Description and Xpath
Citations

The most common use of CI_OnlineResources in the ISO Standards is as part of CI_Citations. This is a new addition in ISO 19115-1 and it makes it much easier to cite resources from the web.

//mcc:CI_Citation/mcc:onlineResource

Contact Information

A second common use of CI_OnlineResources in the ISO Standards is as part of a CI_ResponsibleParty object in CI_Citations. In ISO 19115, this is the only CI_OnlineResource associated with a CI_Citation it can give be the Home Page for the contact.

//gmd:CI_Citation/gmd:citedResponsibleParty /gmd:CI_ResponsibleParty/gmd:contactInfo/gmd:CI_Contact /gmd:onlineResource

Digital Transfer Options

The CI_OnlineResource in the MD_DigitalTransferOptions is the location of digital resources distributed over the Web.

/gmi:MI_Metadata/gmd:distributionInfo/gmd:MD_Distribution/gmd:transferOptions/gmd:MD_DigitalTransferOptions/gmd:online
or
/gmi:MI_Metadata/gmd:distributionInfo/gmd:MD_Distribution/gmd:distributor/gmd:MD_Distributor/gmd:distributorTransferOptions/gmd:MD_DigitalTransferOptions/gmd:online

Services

The CI_OnlineResource in the SV_OperationMetadata is the URL for a service operation (e.g. GetCapabilities, GetMap).

/gmi:MI_Metadata/gmd:identificationInfo/srv:SV_ServiceIdentification/srv:containsOperations/srv:SV_OperationMetadata/srv:connectPoint/gmd:CI_OnlineResource

Extensions

The CI_OnlineResource in the MD_MetadataExtensionInformation is the location of the description of extensions used in the metadata record.

/gmi:MI_Metadata/gmd:metadataExtensionInfo/gmd:MD_MetadataExtensionInformation/gmd:extensionOnlineResource

Crosswalks

All of these approaches to describing online resources include properties that make links more self-explanatory and easier to use.
ConceptDescriptionDialect (Fit) Paths
URLAddress of the online resourceDIF /dif9:DIF/dif9:Related_URL/URL
ECHO /*/echo:OnlineAccessURLs/echo:OnlineAccessURL/echo:URL
ECHO /*/echo:OnlineResources/echo:OnlineResource/echo:URL
EML /eml:dataset/eml:distribution/eml:online/eml:url/eml:text
FGDC /fgdc:metadata/fgdc:idinfo/fgdc:citation/fgdc:citeinfo/fgdc:onlink
ISO //gmd:CI_OnlineResource/gmd:linkage/gmd:URL
ISO-1 //cit:CI_OnlineResource/cit:linkage/gco:CharacterString
UMM /umm:UMM/umm:RelatedURL/umm:URL
OGC-SOS /sos:Capabilities/ows:OperationsMetadata/ows:Operation/ows:DCP/ows:HTTP/ows:Get/@xlink:href
OGC-SOS /sos:Capabilities/ows:OperationsMetadata/ows:Operation/ows:DCP/ows:HTTP/ows:Post/@xlink:href
SERF /serf:SERF/serf:Service_Citation/serf:URL
THREDDS //thredds:dataset/thredds:documentation/@xlink:href
Online Resource DescriptionA brief description of the online resourceDIF (1) /dif9:DIF/dif9:Related_URL/dif9:Description
ECHO (1) /*/echo:OnlineAccessURLs/echo:OnlineAccessURL/echo:URLDescription
ECHO (1) /*/echo:OnlineResources/echo:OnlineResource/echo:Description
ISO (1) //gmd:CI_OnlineResource/gmd:description/gco:CharacterString
ISO-1 //cit:CI_OnlineResource/cit:description/gco:CharacterString
UMM (1) /umm:UMM/umm:RelatedURL/umm:Description
Online Resource FunctionA description of the function of the online resourceECHO (1) /*/echo:OnlineResources/echo:OnlineResource/echo:Type
ISO //gmd:CI_OnlineResource/gmd:function/gco:CI_OnLineFunctionCode
ISO-1 //cit:CI_OnlineResource/cit:function/cit:CI_OnLineFunctionCode
Online Resource Name/TitleA name or title of the online resourceDIF /dif9:DIF/dif9:Related_URL/dif9:URL_Content_Type/dif9:Type > /dif9:DIF/dif9:Related_URL/dif9:URL_Content_Type/dif9:Subtype
ISO //gmd:CI_OnlineResource/gmd:name/gco:CharacterString
ISO-1 //cit:CI_OnlineResource/cit:name/gco:CharacterString
THREDDS //thredds:dataset/thredds:documentation/@xlink:title
Format of the Online ResourceIdentify the format of the online resourceECHO /*/echo:OnlineAccessURLs/echo:OnlineAccessURL/echo:MimeType
ECHO (1) /*/echo:OnlineResources/echo:OnlineResource/echo:MimeType
ISO //gmd:CI_OnlineResource/gmd:applicationProfile/gco:CharacterString
ISO-1 //cit:CI_OnlineResource/cit:applicationProfile/gco:CharacterString
UMM /umm:UMM/umm:RelatedURL/umm:MimeType

xPath Note: The xPaths included in this table use several wildcards. // means any path, so //gmd:CI_ResponsibleParty indicates a gmd:CI_ResponsibleParty anywhere in an XML file. /*/ indicates a single level with several possible elements. This usually indicates one of several concrete realizations of an abstract object. For example /*/gmd:identificationInfo could be gmd:MD_Metadata/gmd:identificationInfo or gmi:MI_Metadata/gmd:identificationInfo and gmd:identificationInfo//*/gmd:descriptiveKeywords could be gmd:identificationInfo/gmd:MD_DataIdentification/gmd:descriptiveKeywords or gmd:identificationInfo/srv:SV_ServiceIdentification/gmd:descriptiveKeywords.

Notes

All of these approaches to describing online resources include properties that make links more self-explanatory and easier to use. There are some differences that need to be considered when comparing them:

  1. Types and Function Codes - All three dialects include a mechanism for classifying online resources. DIF and ISO use shared vocabularies and ECHO uses free text. The DIF vocabulary is hierarchical and includes roughly 35 choices. The ISO codeList includes 11 broad categories. The ECHO Collection metadata currently includes roughly 45 different values with some overlap with the DIF list. Given the variation in these existing approaches, it seems reasonable to map the DIF and ECHO types into the ISO name element, which is free text, rather than into the function element which is a codeList.

All of these approaches to describing online resources include properties that make links more self-explanatory and easier to use.