ELink:  Checks for the existence of an external or Related Articles link from a list of one or more primary IDs;  retrieves IDs and relevancy scores for links to Entrez databases or Related Articles; creates a hyperlink to the primary LinkOut provider for a specific ID and database, or lists LinkOut URLs and attributes for multiple IDs.

• URL Parameters
• Examples
• List of Links in Entrez
• System Requirements for Utility Users
• Entrez DTDs
• Demonstration Program
• Announcement Mailing List
• Questions?

Base URL: http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?

URL parameters: (Note: utility parameters may be case sensitive, therefore, use lower case characters in all parameters except for WebEnv.

• Database (db)
• Record Identifier (id) 
• Relative Date (reldate) 
• Date Range (mindate, maxdate)  
• Date Type (datetype) 
• Search Limits (term) 
• Retrieval Mode (retmode) 
• To Database (db) 
• From Database (dbfrom)  
• Web Environment (WebEnv)
• Query_key (query_key) 
• Holdings (holding)
• Link Command (cmd)
• Version (version)
• Tool (tool)
• E-mail Address (email)

Database (db) databases available from EInfo

• db=

Record Identifier: Required if WebEnv is not used.

• id=12345,92932,828282&id=1234

• ID groups are defined and separated by &id=
• IDs within an ID group are separated by commas
• Each ID group result set is processedseparately,e.g.,id=1234&id=12345 generates separate result lists
• To display a single result list create one ID group, e.g., id=1234,12345

PMID (pubmed)
MIM number (omim)
GI number (nucleotide, protein)
Genome ID (genome)
Popset ID (popset)
SNP cluster ID (snp)
UniSTS ID (unists)
UniGene cluster ID (unigene)
MMDB-ID (structure)
PSSM-ID (cdd)
3D SDI (domains)
TAXID (taxonomy)
GEO ID (geo)

Date Parameters (onlyvalidfordbfrom=pubmed&cmd=neighbor)

Relative Dates: Limit items to the number of days immediately preceding today's date.

• reldate=

reldate=90
reldate=365

---

• mindate=
• maxdate=

mindate=2001
maxdate=2002/01/01

---

• datetype=

datetype=edat
datetype=mdat

---

• term=

term=medline[sb]
term=human[organism]
term=biomol genomic[properties]

---

• retmode=

retmode=xml (default)
retmode=ref (only used with cmd=prlinks)

To Database: ELink 'linking to' or destination database, pubmed is the default db. To retrieve links for all Entrez databases use db=all.

• db=

From Database: ELink 'linking from' or origination database, pubmed is the default db.

• dbfrom=

Web Environment: Value previously returned in XML results from ESearch and EPost and used with ELink in place of primary ID result list. Required if id is not used.

• WebEnv=

• query_key=

• cmd=

• cmd=prlinks - List the hyperlink to the primary LinkOut provider for multiple IDs and database. Each ID is processed separately.
• cmd=prlinks&retmode=ref - Create a hyperlink to the primary LinkOut provider for a single ID and database.
• cmd=llinks - List LinkOut URLs and Attributes, except PubMed libraries, for multiple IDs and database. Each ID is processed separately.
• cmd=llinkslib - List LinkOut URLs and Attributes for multiple IDs and database. Each ID is processed separately.
• cmd=lcheck - Check for the existence (Y or N) of an external link in for multiple IDs and database.
• cmd=ncheck - Check for the existence of a neighbor link for each ID within a database, e.g., Related Articles in PubMed.
• cmd=neighbor - Display neighbors within a database.
• cmd=neighbor_history - Create history (WebEnv & query_key) for use in other EUtilities.
• cmd=acheck - Lists Entrez databases links for multiple IDs from a single database.

• Use linkname to link to a specific neighbor subset, e.g., linkname=nucleotide_nucleotide_comp
• A full list of allowed link names is available here - Entrez Links List
• Date limits are not valid for Link Commands.
• The default Command Value is cmd=neighbor.

Holdings: List LinkOut URLs for the specified holding provider, e.g., library. Used only in conjunction with cmd=llinks or cmd=llinkslib

• holding=

For example:

cmd=llinkslib&holding=medlib

Version: Include a version number to refer to the latest DTD.

• version=

For example:

version=1 retrieves the latest DTD (eLink_050511.dtd) that includes the additional elements, MenuTag, LinkInfo and IdLinkSet.

• tool=

• email=

Examples:

To retrieve IDs from PubMed for PMID  9298984 to the PubMed database:
http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&id=9298984&cmd=neighbor

To retrieve IDs from CoreNucleotide for GI  48819, 7140345 to Protein:
http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=nuccore&db=protein&id=48819,7140345

To retrieve PubMed related articles for PMIDs 11812492 11774222 with a publication date from 1995 to the present:
http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&id=11812492,11774222&db=pubmed&mindate=1995&datetype=pdat

To retrieve MEDLINE indexed only related articles for PMID 12242737:
http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&id=12242737&db=pubmed&term=medline[sb]

To create a hyperlink to the first link available for PMID 10611131 in PubMed:
http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&id=10611131&retmode=ref&cmd=prlinks

To list all available links in PubMed, except for libraries, for PMIDs 12085856 and 12085853:
http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&id=12085856,12085853&cmd=llinks

To list Entrez database links for PubMed PMIDs 12169658 and 11748140:
http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&id=12169658,11748140&cmd=acheck

To check for the existence of a Related Articles link for PMIDs 0611131, 111645 and 12068369:
http://eutils.ncbi.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&id=10611131,111645&id=12068369&cmd=ncheck

To create history (WebEnv & query_key) for Protein GI 50806715, 50810195 neighbors from Nucleotide and Taxonomy:
http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?id=50806715&id=1698399&cmd=neighbor_history&dbFrom=protein&db=nuccore,taxonomy

To retrieve neighbors for Cancer Chromosomes ID 2662 to the link subset related by cytogenetics:
http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=cancerchromosomes&db=cancerchromosomes&id=2662&cmd=neighbor&linkname=cancerchromosomes_cancerchromosomes_cyto