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Element Description

The Related URLs element, when accompanied by the 'get data' sub-elements, is used to link directly to a data access point. This is different from a USE SERVICE API URL, which relates to methods of sub-setting and/or transforming data before obtaining it. For details concerning USE SERVICE API URLs, please see the Related URLs (USE SERVICE API) wiki page. 

For general Related URL guidance (not specific to service data access links), please refer to the Related URLs wiki page.

Best Practices

The GET DATA Related URL metadata element allows for the linkage of a metadata record to a location on the web where data may be directly accessed. As mentioned on the Related URLs wiki page, there are several sub-elements which are used to identify the purpose of the URL. For GET DATA links specifically, best practices for these elements include:

URL Content Type: The URL Content Type is a keyword which, at a high level, describes the content of a link. This is a controlled vocabulary field maintained as an enumeration list within the UMM-Common schema. For GET DATA URLs, the URL Content Type should always be "DistributionURL".

URL Type: The URL Type is a keyword which specifies the content of a link. URL Type keywords are maintained in the Keyword Management System (KMS). For GET DATA URLs, the URL Type should always be "GET DATA".

URL Subtype: The URL Subtype is a keyword which further specifies the content of a link. Together, the URL Type and Subtype keywords create a keyword hierarchy which is used to identify the URL. Providing a Subtype for GET DATA URLs is optional, but should be used when applicable. Subtype keywords can be found in the URL Content Type keyword list. For access links, any Subtype keyword after GET DATA is a valid option.

Description: While not required, it is highly recommended that a description be provided for each URL provided in the metadata. The description should be kept brief and explain to the user that the link goes to a data access point. The descriptions should be unique to the link. While descriptions can be repeated for the same type of URL across different metadata records, it is generally advised that the same description not be repeated within the same metadata record. I.e. the description should be used to further differentiate two GET DATA URLs with the same URL Type and Subtype. 

There are several sub-elements specifically designated for GET DATA URLs. The following provides definitions and best practices for each of the sub-elements:

RelatedUrls/GetData/Format: The format of the data provided via the associated URL. Format is an optional sub-field. Format is a controlled vocabulary field and should be chosen from the <insert GCMD data format keyword list>. If data is provided in a compressed file format (e.g. .zip, .tar), it is recommended that the format of the data once it is uncompressed be provided.    

RelatedUrls/GetData/MimeType: MIME stands for "Multipurpose Internet Mail Extensions". Mime types are used to identify the nature and format of files provided on the Internet, and are typically used by internet browsers in order to determine how to properly process or display a document or file. Providing the Mime Type element in the metadata helps ensure that the URL contents will be properly displayed on the Web. Mime Type is an optional sub-field. Mime Type is a controlled vocabulary field and should be chosen from the <insert GCMD mime type keyword list>.   

RelatedUrls/GetData/Fees: The fee (if any) for ordering the data. The fee should be a number in U.S. dollars. This is an optional field.  

The following GET DATA sub-elements only apply when the data access link is a direct download (i.e. when clicking on the URL results in an immediate download). For example, the following URL is a direct download (warning: clicking on this link will result in a file to be downloaded to your work space (203.6 MB). An Earthdata login is required to access the file): https://daac.ornl.gov/cgi-bin/download.pl?ds_id=1574&source=dsviewer 

These GET DATA sub-elements include:

RelatedUrls/GetData/Size: The purpose of this element is to inform users of the size of the data that will be downloaded to their local work space if they click on the data access URL. This element only contains the numerical value of the size, not the unit. The unit (e.g. KB, MB, etc.) should be provided in the 'Unit' element.      

RelatedUrls/GetData/Unit: The unit accompanying the size specified in the 'Size' element. Together, Size and Unit indicate the size of the data file(s) to be downloaded via the provided URL. Unit must be provided if 'Size' is provided. Unit is a controlled vocabulary field and must be selected from the following options: KB, MB, GB, TB, PB. 

RelatedUrls/GetData/Checksum: A value used to verify the integrity of a file or a data transfer, such as the integrity of a downloaded file. The checksum provided in the metadata may be used to compare the original data file to the copy of the data downloaded to a user's local work space. The checksum provided in the metadata should be that of the original data file. The user is responsible for generating a checksum of the file on their local work space. If the checksum generated on their local work space does not match the checksum in the metadata (i.e. the original file), the data may have been altered or corrupted. Note that there are a variety of checksum algorithms available for use. Some examples include: MD5, CRC-8, CRC-16, CRC-32, Feltcher's checksum, Alder-32.  

For NASA EOSDIS data sets:

• At least one GET DATA URL is required for all NASA EOSDIS data sets. 
• For NASA EOSDIS data, data access should be behind Earthdata Login authentication. 
• For NASA EOSDIS data, data access should not be provided via FTP, in favor of the HTTPS protocol.

Examples:

URL: https://hydro1.gesdisc.eosdis.nasa.gov/data/FLDAS/FLDAS_VIC025_C_EA_M.001/

URL Content Type: DistributionURL

URL Type: GET DATA

URL Subtype: DATA TREE

Description: Use the link to access the data via HTTPS. Files are organized by date.

Format: NetCDF-4 

Mime Type: text/html 

Fees: 0

URL: https://daac.ornl.gov/cgi-bin/download.pl?ds_id=465&source=dsviewer

URL Content Type: DistributionURL

URL Type: GET DATA

URL Subtype: DIRECT DOWNLOAD

Description: Downloads the NPP Boreal Forest: Canal Flats, Canada, 1984, R1 data set directly to your workstation. 

Format: Text File 

Size: 91.8

Unit: KB

Fees: 0

Checksum: f2aa78d6825ec42d783581a8d5ea1f 68

Metadata Validation and QA/QC

All metadata entering the CMR goes through the below process to ensure metadata quality requirements are met. All records undergo CMR validation before entering the system. The process of QA/QC is slightly different for NASA and non-NASA data providers. Non-NASA providers include interagency and international data providers and are referred to as the International Directory Network (IDN).

Please see the expandable sections below for flowchart details.

Dialect Mappings

UMM Migration

None

Future Mappings

RelatedUrls: [
  {
    Description: "Use the link to navigate and download data files organized by date.",
    URLContentType: "DistributionURL",
    Type: "GET DATA",
    Subtype: "DATA TREE",
    URL:  "https://oco2.gesdisc.eosdis.nasa.gov/data/s4pa/OCO2_DATA/OCO2_L2_Met.8r/",
   -GetData: {
      MimeType: "text/html"
    }
  }
]

History

UMM Versioning

ARC Documentation