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Frequently Asked Questions for LinkOut Providers
Last Updated: December 1, 2003
LinkOut is a feature of Entrez that is designed to provide users with links from PubMed and other Entrez databases to a wide variety of relevant web-accessible online resources, including full-text publications, databases, research tools, and more. The links are supplied by third party resource providers who choose to participate in the LinkOut project.
General
LinkOut Files
General
Will my resources be appropriate for LinkOut?
LinkOut resources must be useful to Entrez users' research.
They should be directly relevant to specific subjects of the Entrez records
that they will be linked to. The information and its
delivery system should be of high quality, and must not, through typographic
or factual errors, omissions, or other flaws or inconsistencies, mislead,
hinder or frustrate the research efforts of Entrez users. The resources
should be easy to use and navigate.
Can I restrict access to my resources?
Absolutely. Access authentication and authorization is the decision of a resource provider. However, if there is restriction for access, the attribute "subscription/.membership/fee required" should be used to inform Entrez users about the restriction.
Full-text providers that provide free access to their summary pages,
but restrict full text access to subscribers, may choose to provide links
to their summary pages that have links to the full-text. If they do so,
they should include the attributes "full-text online" and "subscription/membership/fee
required" to let users know the full text is available in addition to the
summary.
What level of linking should I provide?
Links should be directed to the resource itself, not its surrogate or
container. For example, a full-text provider should provide links
to the full-text electronic articles, not the table of contents or the
home page of an electronic journal.
Can my resources be linked to all Entrez records?
LinkOut resources must be specialized to be of value in Entrez users'
research and not overburden NCBI's system. Thus, linking to all records in an
Entrez database without selection is not allowed.
What responsibilities do I have as a LinkOut provider?
A LinkOut provider must make sure that both their resources and links
are of high quality and functional.
There must not be any blind or broken links, or links that lead to the wrong
targets. The provider is also responsible for transferring
any additions, changes and deletion of their links to NCBI.
NCBI provides the links in Entrez and promotes the LinkOut feature.
However, it is the responsibility of the provider to promote their
resources to their existing and potential users.
Are there any prerequisite for submitting links?
Publisher of journals included in PubMed must submit their citation data electronically
BEFORE they submit links to their web-accessible full-text. Please see the
Information for Publishers documentation for details about submitting electronic data to PubMed.
An icon that represents links to the publisher's full-text will then display by default
on the PubMed Abstract and Citation Display.
Will my links be shown on systems besides Entrez?
Besides the Entrez system, all LinkOut resources are also available through the Entrez Programming Utilities - ELink. Thus, systems other than Entrez may get your links through this utility and display them at their sites.
What do I need to do to provide links to my resources?
A potential provider should contact NCBI at linkout@ncbi.nlm.nih.gov to express
their interest in LinkOut. Two types of LinkOut files,
Identity and Holdings files are required. For help in preparing these files, please
consult one of the following documents:
LinkOut and Publisher Holdings, LinkOut
and Library Holdings
and LinkOut and Non-Bibliographic
Resources.
How does LinkOut relate to services based on OpenURL?
LinkOut is the Entrez feature to handle external linking in PubMed and other
Entrez databases, including services based on OpenURL. The document
PubMed and OpenURL-based Services provides additional
information on this topic.
LinkOut Files
What are the LinkOut Identity and Holdings Files?
They are types of LinkOut files. The
Identity File provides identity information about a LinkOut resource provider.
The Holdings File describes the links to the resources and the Entrez records
the links will apply to.
How should I select a NameAbbr?
NameAbbr is a short, preferably less than 8 characters, one word abbreviation for
a provider. It may only include alpha and numeric characters,
spaces and special characters such as hyphens are not allowed.
Are the elements in LinkOut files case sensitive?
Like all valid XML elements, elements in LinkOut files are case-sensitive.
Please use the element tags exactly as they are specified in the
LinkOut.dtd
How can I use the elements: SubjectType, Attribute and UrlName?
SubjectType and Attribute can be used to describe the resources listed in the Holdings file and the relationship of the provider to the resources. The list of allowable terms for these two elements is available at LinkOut SubjectTypes, Attributes and UrlName
A free-form text string can be used in UrlName to further describe the
resources in case the allowed terms for SubjectType and Attribute are not
sufficient.
What is the difference between the SubjectType and Attribute elements in the Identity file and those in the Holdings files?
SubjectTypes and Attributes included in the Identity file will apply
to all the holdings provided by a provider. If they are included inside a link
in the Holdings file, they will only apply to that specific link.
How do the Base and URL elements work?
LinkOut simply concatenates whatever is input in the Base and URL elements to form a link to your resource. Typically, the consistent part of your resource URL should be entered in the Base element, and the variable part of the URL should be entered in the Rule element. Please be careful not to put extra or missing characters at the beginning or the end of these elements.
You may also make use of an entity in the
Prolog of the LinkOut files
to save some typing.
How can users see our links in the Entrez databases?
All external links from an Entrez record are listed in the LinkOut display,
which is accessible from the Display pull-down menu, or by clicking
"LinkOut" from the Citation and Abstract display formats.
How can users see our LinkOut icon in the Entrez databases?
At this point, only PubMed will display an icon from a provider. To see a provider's icon, one need to invoke PubMed using the following URL:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?holding=provider
where "provider" is a provider's NameAbbr.
The provider's icon will then display on the Citation and Abstract display of the records that a provider has specified in their Holdings file.
Alternatively, users can use
Cubby to select the icon to display.
Which icon will display by default on the Citation and Abstract display of PubMed?
The icon for publishers that provide electronic citation data to PubMed
will display by default on the Abstract and Citation display of PubMed. These publishers should specify in their Identity
files the SubjectType
"publishers/providers", and the Attribute "publisher of information in URL".
How should I design the LinkOut icon for my organization?
The recommended size of a LinkOut icon is 100 pixels in width and 25 pixels
in height. Icon larger than 150 pixels in width and 35 pixels in height will
be scaled down. The icon should look like a button. An icon with a white or
transparent background, or without borders, is not recommended.
Can I put the icon in a HTML page and supply its URL in the IconUrl element?
No. You should provide a URL pointing directly to the image file,
e.g. http://www.linksprovider.org/icondirectory/lo-icon.gif.
Please do NOT include the icon in a HTML page.
What is the difference between the IconUrl element in the Identity file and that in the Holdings file?
Only the icon specified in IconUrl in the Holdings file will be displayed
in PubMed. Icon specified in the Identity file is not used at this point.
What happens if I do not have an icon for my links?
LinkOut will provide a default "Go to Publisher's Site" icon if
there is no IconUrl element or the element is left blank in a Link.
How can I update our LinkOut files after the initial transfer?
A provider may transfer new versions of current LinkOut files or add
new Holdings files at any time. It is the responsibility of the provider
to keep its files current and valid. Links in the Entrez databases,
are regenerated each day based on the Holdings files in each provider's
directory. Providers should delete obsolete files from their directories.
How can I keep up with the development of LinkOut?
You may subscribe to the linkout-news announcement mailing list.
To subscribe send an e-mail message with subscribe in the Subject to:
linkout-news-request@ncbi.nlm.nih.gov
or subscribe on the web at:
http://www.ncbi.nlm.nih.gov/mailman/listinfo/linkout-news
Libraries may also subscribe to the library-linkout announcement
mailing list.
To subscribe send an e-mail message with subscribe in the Subject to:
library-linkout-request@ncbi.nlm.nih.gov
or subscribe on the web at:
http://www.ncbi.nlm.nih.gov/mailman/listinfo/library-linkout
Taxonomic resource providers may also subscribe to the tax-linkout announcement mailing list.
To subscribe send an e-mail message with subscribe in the Subject to:
tax-linkout-request@ncbi.nlm.nih.gov
or subscribe on the web at:
http://www.ncbi.nlm.nih.gov/mailman/listinfo/tax-linkout
Send questions and comments to linkout@ncbi.nlm.nih.gov