External Link


Link to an external file, such as MEDLINE, GenBank, etc.


Use the standard XLink attributes to provide a live link to the external source.

The ext-link-type attribute can be used to give an indication of the type of resource to which the external link points. While the DTD does not constrain the values of this attribute, and ordinary text is acceptable, the suggested values include:


Enzyme nomenclature. See http://www.chem.qmw.ac.uk/iubmb/enzyme/


GenBank identifier


Translated protein-encoding sequence database


HighWire Press intrajournal


MEDLINE or PubMed identifier


Protein data bank. See http://www.rcsb.org/pdb/


Plant gene register. See http://www.tarweed.com/pgr/


Protein Information Resource. See http://pir.georgetown.edu


Protein Information Resource. See http://pir.georgetown.edu


Used to link between articles in PubMed Central (access is PMID)


Swiss-Prot. See http://www.ebi.ac.uk/swissprot/


Astronomical Object Identifier


Digital Object Identifier


File transfer protocol


Website or web service


ext-link-type Type of External Link
id Identifier
xlink:actuate Actuating the Link
xlink:href Href (Linking Mechanism)
xlink:role Role of the Link
xlink:show Showing the Link
xlink:title Title of the Link
xlink:type Type of Link
xmlns:xlink XLink Namespace Declaration

Related Elements

The <self-uri> element is used when an article is available in multiple forms, for example, as a means of indicating the PDF version of a print article. Conversely, a URI that indicates a different article or any other kind of external reference is usually tagged with the <ext-link> element. The element <uri>, although allowed everywhere <ext-link> is used, is more typically part of an address, information concerning a contributor, or part of a reference citation. Loosely put, an external link <ext-link> is intended to act as a link; a URI <uri> makes no promises but identifies a URI, such as a URL, when it is present in the text of an address or a citation; and <self-uri> points to another form of the same article.

The address element <email> is allowed as part of a paragraph as well as inside an address. There are two ways to treat an email address in text: as and <email> element or as and <ext-link> element. If both a textual phrase (“the Moody Institute’s email address”) and a mailto URL are required, the <ext-link> element should be used.

An address (<address>) may use the following elements, in order: <institution>, <addr-line>, <country>, <phone>, <fax>, <email>, <ext-link>, and <uri>. At minimum, the element <country> must be used.

Model Information

Content Model

<!ELEMENT  ext-link     (#PCDATA %ext-link-elements;)*               >


Any combination of:

This element may be contained in:

<address> Address/Contact Information; <aff> Affiliation; <article-title> Article Title; <attrib> Attribution; <bold> Bold; <chem-struct> Chemical Structure (Display); <citation> Citation; <collab> Collaborative (Group) Author; <comment> Comment in a Citation; <contrib> Contributor; <copyright-statement> Copyright Statement; <def-head> Definition List: Definition Head; <disp-formula> Formula, Display; <inline-supplementary-material> Inline Supplementary Material; <italic> Italic; <monospace> Monospace Text (Typewriter Text); <named-content> Named Special (Subject) Content; <overline> Overline; <p> Paragraph; <preformat> Preformatted Text; <product> Product Information; <related-article> Related Article Information; <sc> Small Caps; <source> Source; <strike> Strike Through; <sub> Subscript; <subtitle> Article Subtitle; <sup> Superscript; <supplementary-material> Supplementary Material; <td> Table Data Cell (XHTML table model); <term> Definition List: Term; <term-head> Definition List: Term Head; <th> Table Header Cell (XHTML table model); <title> Title; <trans-source> Translated Source; <trans-title> Translated Title; <underline> Underline

Tagged Example

<sec sec-type="intro">
<p>... The highest 16S rDNA sequence similarity 
value of 98&amp;amp;#x0025; was obtained for the 
<italic>D. maris</italic> 16S rDNA sequence 
(GenBank accession no. <ext-link ext-link-type="gen"
xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="Y18883"/>) 
and for the <italic>D. maris</italic> DSM 43672<sup>T</sup> 
16S rDNA sequence (GenBank accession no. <ext-link 
ext-link-type="gen" xmlns:xlink="http://www.w3.org/1999/xlink"
xlink:href="X79290"/>) ....</p>