The <Reference> field describes key bibliographic citations pertaining to the service.

Bibliographic citations may be populated as a block of text in the free-text field or as text in subfields (see below). Citations in the free-text field may be provided in styles used by professional scientific journals such as the American Geophysical Union (AGU), American Psychological Association (APA), or Modern Language Association (MLA).

Subfields:

• <Author> The name of the individual(s) or organization(s) with primary intellectual responsibility for the cited resource's development.
• <Publication Date> The publication/reference date for the cited resource.  If the Publication Date is not known, please use "Unknown".
• <Title> The title (name) of the cited resource.
• <Series> The name of a resource series, or aggregate (collection) resource of which the cited resource is a part.
• <Edition>  The version of a cited resource.
• <Volume> The order or sequence of a resource in a series or set.
• <Issue> The issue number of a resource (usually within a volume).
• <Report_Number> The unique number or code assigned to a resource by the issuing organization(s).
• <Publication_Place> The name of the city (and state or province and country if needed) where the resource was made available.
• <Publisher> The name of the individual(s) or organization(s) that made the resource available.
• <Pages> The range of pages or total number of pages of a cited resource.
• <ISBN> International Standard Book Number.
• <DOI> Digital Object Identifier.
• <Online_Resource> The URL of the online resource containing the cited resource.
• <Other_Reference_Details>Additional free-text reference information.

<Reference>text</Reference>

OR

<Reference>
<Author>Text up to 500 characters</Author>
<Publication Date>Text up to 31 characters, yyyy-mm-dd format suggested</Publication Date>
<Title>Text up to 220 characters</Title>
<Series>Text up to 220 characters</Series>
<Edition>Text up to 31 characters</Edition>
<Volume>Text up to 80 characters</Volume>
<Issue>Text up to 80 characters</Issue>
<Report_Number>Text up to 80 characters</Report_Number>
<Publication_Place>Text up to 80 characters</Publication_Place>
<Publisher>Text up to 500 characters</Publisher>
<Pages>Text up to 31 characters</Pages>
<ISBN>Text up to 220 characters</ISBN>
<DOI>Digital Object Identifier (DOI) up to 220 characters</DOI>
<Online_Resource>Uniform Resource Locator (URL) up to 600 characters</Online_Resource>
<Other_Reference_Details>Text up to 220 characters</Other_Reference_Details>
</Reference>

Reference with subfields:

• The <Reference> field is recommended and can be repeated.
• The <Author> field is required if the <Reference> field is populated and is not repeatable.
• The <Publication Date> field is required if the <Reference> field is populated and is not repeatable.
  
• The <Title> field is required if the <Reference> field is populated and is not repeatable.
• The <Series> field is optional and is not repeatable.
• The <Edition> field is optional and is not repeatable.
• The <Volume> field is optional and is not repeatable.
• The <Issue> field is optional and is not repeatable.
• The <Report_Number> field is optional and is not repeatable.
• The <Publication_Place> field is optional and is not repeatable.
• The <Publisher> field is optional and is not repeatable.
• The <Pages> field is optional and is not repeatable.
• The <ISBN> field is optional and is not repeatable.
• The <DOI> field is optional and is not repeatable.
• The <Online_Resource> field is optional and is not repeatable.
• The <Other_Reference_Details> field is optional and is not repeatable.

Reference without subfields:

• The <Reference> field is recommended and may be repeated.
• Multiple lines of text are allowed. Characters may be selected from the UTF-8 character set.

Reference with subfields:

<Reference>
<Author>Owen, John B and Alice K. Owen</Author>
<Publication Date>1995</Publication Date>
<Title>A bibliography of fisheries biology in North and South Dakota</Title>
<Edition>2</Edition>
<Publication_Place>Jamestown, ND</Publication_Place>
</Reference>

<Reference>
<Author>Downs, R.T., and Heese, P.J.</Author>
<Publication Date>2000</Publication Date>
<Title>Animation of crystal structure variations with pressure, temperature and composition</Title>
<Series>Reviews in Mineralogy and Geochemistry</Series>
<Volume>41</Volume>
<Publication_Place>Washington DC</Publication_Place>
<Publisher>Mineralogical Society of America</Publisher>
</Reference>

Reference without subfields:

<Reference>
Crum, T.D., and R.L. Alberty, 1993: The WSR-88D and the WSR-88D Operational Support Facility. Bull. Amer. Meteor. Soc., 74, 
1669-1685.
</Reference>

<Reference>
Crum, T.D., R.L. Alberty, and D.W. Burgess, 1993: Recording, 
Archiving, and Using WSR-88D Data. Bull. Amer. Meteor. Soc., 
74, 645-653.
</Reference>

<Reference>
Klazura, G.E., and D.A. Imy, 1993: A Description of the Initial 
Set of Analysis Products Available from the NEXRAD WSR-88D System.
Bull. Amer. Meteor. Soc., 74, 1293-1311.
</Reference>

<Reference>
Cooper, A.K., 1995, Strides made in understanding Antarctic 
stratigraphy and Cenozoic glacial history, Eos Transactions AGU, 
March 7, 1995, p.97.
URL; http://earth.agu.org
</Reference>