Since March 1998, the U.S. Government Printing Office (GPO) has used persistent uniform resource locators (PURLs) to provide libraries and other parties stable URLs to online Federal information. GPO's PURL implementation is utilized by Federal depository libraries, Federal agencies, and others to provide persistent links to Federal resources.
In August 2009, GPO's PURL server experienced a significant hardware failure and was unavailable for an extended period. When this happened, all PURL links became inaccessible. The PURL system is a critical tool of the Federal Depository Library Program that fulfills its mission of providing permanent public access to Federal information resources. As a result of the outage, GPO took steps to ensure high availability and redundancy of the PURL application.
Rearchitecture of PURL Software and Hardware
In order to ensure high availability and redundancy, GPO migrated from the original OCLC PURL Resolver Software to the PURLZ Resolver Software, which is a re-architecture of the original OCLC PURL Resolver Software. Included with the migration is the implementation of an improved hosting solution that provides higher availability for the PURL application. Previously, (ro)bot traffic severely hindered the performance of the PURL application and prevented GPO staff from being able to access the system and add/modify PURLs. Under the new hosting solution, the public's and GPO's access is ensured, while still allowing access to traffic, which mostly consisted of link validators.
New PURL Web Address
A new URL of purl.fdlp.gov has been established due to the sunsetting of GPO Access. This new URL ties PURLs to the Federal Depository Library Program. As a result:
- All new PURLs will use the purl.fdlp.gov address.
- Direct requests to purl.fdlp.gov will go to a splash page. The domain is used to resolve to Federal resources.
- All of the 125,000 PURLs that were created using the original OCLC PURL Resolver Software will continue to resolve. No changes will need to be made (at this time) to the existing records that have been made by Federal depository libraries or GPO.
Automated and Enhanced PURL Referral Reporting
As a follow-up from the November 2009 modification of the PURL referral definition and reporting system, an automated PURL referral reporting system was launched on December 1, 2010 that allows Federal depository libraries to view their institution's referrals by individual hostnames and/or IP addresses. The tool also provides a listing of the top fifty (50) referred PURL resources per hostname and/or IP address with:
- The PURL path.
- The full path of the target URL for each PURL.
- The total requests for that individual PURL.
- A search link utilizing the CGP to view cataloging records for the individual PURL.
GPO still releases monthly PURL referral reports; however, these reports include aggregate totals only. Referrals totals strip out bot traffic and focuses on patron requests.
The PURL Referral Reporting Tool is locked down to Federal depository libraries only. Data is current as of the previous day. Historical data is available for twelve months. Tool functionality may be expanded in the future to include greater historical data retention and additional functionality based on funding and community feedback.
The PURL application features high availability and failover services. Traffic routing has been optimized to permit PURL resolution as well as search engines and link checkers.
Learn how Federal depository libraries can utilize PURLs at their institution, more about how PURLs operate, and information on the PURL referral reporting tool, by reading Linking to Federal Resources Using Persistent Uniform Resource Locators (PURLs).