PURLs

Purls can refer to more than one concept, depending on the context. In knitting, a purl is a basic stitch that forms the opposite texture of a knit stitch. Purls is the plural form used when counting or describing multiple stitches. The purl stitch is typically worked by working yarn over the needle in a way that creates a bumped, ridged surface. Purls are fundamental to many knitting patterns and are often combined with knit stitches to create various fabrics and textures.

In digital libraries and information science, PURL stands for Persistent Uniform Resource Locator. A PURL is a URL designed to remain usable over time by using a separate resolver that redirects a stable identifier to the resource’s current location. The idea is to decouple a resource’s identity from its location, so that even if the resource moves, the PURL can be updated to point to the new URL. This provides a mechanism for long-term access and reliable linking in catalogs, archives, and scholarly repositories.

A typical PURL system involves a stable identifier administered by a repository or institution, a resolver service that handles redirection, and metadata describing the resource. PURLs are part of a broader ecosystem of persistent identifier schemes, including DOIs, ARKs, and Handles. While PURLs have historically played a role in digital preservation and link maintenance, many institutions now rely on alternative identifiers or newer services that offer similar persistence guarantees. PURLs continue to be used in some libraries and digital projects where established resolver infrastructure remains in place.