PURL stands for "Persistent Uniform Resource Locator."
Functionally, a PURL is a URL.
Instead of pointing directly to the location of an Internet resource, a PURL points to an intermediate resolution service. The resolution service associates the PURL with the actual URL and returns that URL to the client, which can then complete the transaction in the normal fashion.
In Web parlance, this is a standard HTTP "redirect."
_______ PURL ----------
| | ------------>> | | Resolver associates PURL with
| | | PURL | unique URL; maintenance utilities
| C | URL | SERVER | facilitate creation of PURLs and
| L | <<------------ | | modification of associated URLs.
| I | ----------
| E | URL ----------
| N | ------------>> | |
| T | | RESOURCE |
| | Resource | SERVER |
| | <<------------ | |
-------- ----------
PURLs look just like URLs because they are URLs. A PURL has three parts: (1) the protocol, (2) the resolver address, and (3) a name.
Here are a few examples of PURLs (some are hypothetical):
http://purl.oclc.org/OCLC/RSPD
---- ------------- ---------
/ | \
protocol resolver address name
http://purl.oclc.org/oclc/rsch/metadataII
---- ------------- --------------------
/ | \
protocol resolver address name
http://purl.somewhere.edu/library/catalog
---- ------------------ ---------------
/ | \
protocol resolver address name
http://purl.org/keith/home
---- -------- ----------
/ | \
protocol resolver address name
http://purl.org/net/weibel
---- -------- ----------
/ | \
protocol resolver address name
http://purl.publisher.com/journal/article_id
---- ------------------ ------------------
/ | \
protocol resolver address name
Sometimes URLs do not work because Internet resources move, change names or method of access, or other reasons. Once a URL fails, all instances of that URL (for example, links in a Web document or a bibliographic record) become invalid.
As long at the PURL resolver is functioning, the PURLs never change.
A PURL can be associated with any given resource/URL. While PURLs allow you to associate different URLs with them, the PURL itself never changes. Put another way, you can change what a PURL resolves to, but you can't change the PURL.
This means that a PURL can last longer than any particular URL that may be associated with it. PURLs persist indefinitely, and as long as they do, all instances of such PURLs (for example, links in a Web document or a bibliographic record) remain valid.
A PURL resolver is a service, available via standard HTTP 1.0 protocols, that facilitates the creation, maintenance, and resolution of PURLs.
Domains are subdivisions of the name space on a PURL resolver. They are very much like directories in a file system.
There are two varieties of domains: top-level and subdomains.
The concept of partial redirection is the use of a domain as a prefix for a localized hierarchy of URLs. This is possible because a PURL resolver will resolve as much of a PURL as it can find in its database and append the remainder (unresolved portion) to the end of the resolved URL. For example, if the partial redirect http://purl.foo.com/bar exists and is associated with the URL http://your.web.server/your/servers/web/root then an attempt to resolve the partial redirect PURL http://purl.foo.com/bar/some/other/stuff.html will resolve to the URL http://your.web.server/your/servers/web/root/some/other/stuff.html
A partial redirect is a special-purpose PURL that acts like a domain. A regular domain has no associated URL. While a partial redirect has a URL associated with it, that URL is not guaranteed (or even expected) to reference an actual resource. The URL associated with a partial redirect may only be a prefix common to the complete URLs of multiple resources. In contrast, the URL associated with a PURL is expected to reference a single actual resource.
Anyone with valid a CONSER or BIBCO authorization may become a registered user of the OCLC Bibliographic PURL resolver.
If you want to be able to do any of these things, you must become a registered user. Otherwise, you do not have to become a registered user.
Unregistered users can search the resolver for universally-resolvable PURLs and partial redirects. They cannot do these things.
As a registered user, you can:
Point your Web browser to the OCLC Bibliographic PURL resolver and follow the instructions for becoming a registered user.
Yes. Any CONSER or BIBCO participant can create a PURL.
If you are not a registered user of the Bibliographic PURL resolver, you must become one. You are then able to create PURLs.
To create a PURL, point your Web browser to the OCLC Bibliographic PURL resolver and follow the instructions for creating a PURL.
The PURL name is generated automatically.
None.
A PURL can look very different from its associated URL. For example, suppose the URL for a resource is
http://my.address.org/very/long/path/name/and/obscure/file_name.txtThis URL can be associated with the PURL
http://purl.oclc.org/foo/barIt is not necessary for the PURL name component to duplicate any portion of the associated URL.
Yes. Any CONSER or BIBCO participant registered to use the Bibliographic PURL resolver can create a partial redirect.
If you are not a registered user of the Bibliographic PURL resolver, you must become one.
To create a partial redirect, point your Web browser to the Bibliographic PURL resolver and follow the instructions for creating a partial redirect.
No. No one can or should delete a PURL. A PURL can, however, be associated with a "null URL", i.e., no URL at all, in which case, a history page is returned when the PURL is resolved.
No. Once a domain is created it will persist indefinitely.
No. No one can or should delete a partial redirect. A partial redirect can, however, be associated with a "null URL", i.e., no URL at all, in which case, a history page is returned when the partial redirect is resolved.
A group is a list of registered users, groups, or both. The group all includes all registered users. The Bibliographic PURL resolver has only one group. All registered users are automatically added to the CONSER group.
Groups are mechanisms that allow you to organize and easily specify lists of registered users. This mechanism is useful for specifying other readers, writers, or maintainers of things you own. In and of themselves, groups do not bestow new capabilities on their members.
Group members are registered users who are included in a group.
You and other users in the CONSER group are its maintainers.
You are the only writer of the PURLs and partial redirects you have created. (Creating a PURL or partial redirect is the same as writing it and can only be done once for any PURL or partial redirect.)
You can select a PURL that you find, for example, on a Web page or in a document, and the PURL will be resolved to the associated URL, which your browser will then use to access the resource.
PURLs generated by the Bibliographic PURL resolver will be placed in OCLC's bibliographic records. Your links will remain valid even if the associated URLs change. (This does not mean that a PURL magically changes its own associated URL when the referenced resource moves, you must update your PURLs when this happens.)
You can submit a PURL (or even just part of a PURL) to the PURL resolver to obtain more information about the PURL, the associated URL, or, in some cases, the resource itself.
Avoid using the "save-current-document-as-a-bookmark" feature of most browsers because this will save the URL, not the PURL, of the document. Note that when you access a document via a PURL, it causes a redirect to the associated URL. The URL, not the PURL, is what the browser associates with the "current document" it is displaying. Instead, you should use your browser's manual bookmark editing features to enter PURLs by hand. That way, the PURL, not the URL associated with it, becomes the bookmark.
No. You or another registered CONSER or BIBCO participant must update your PURL when the associated URL changes.
It is the responsibility of a PURL's owner and its maintainers to update the PURL when the associated URL changes. You can update the URL associated with any PURL you created. In addition, you can update any PURL for which you are a maintainer.
You can perform PURL maintenance by connecting to the Bibliographic PURL resolver using a WWW browser and then using the PURL resolver's maintenance forms to make the appropriate changes to the desired PURL.
Any registered CONSER or BIBCO participant can modify the URL associated with a PURL.
No. PURLs are uniquely associated with a single URL at any given moment. Over time, however, the associated URL can change. In other words, a PURL may have many URLs associated with it over time, but only one at a time.
No. The owner of a PURL can change the associated URL at will.
Yes. This will happen when a user creates PURLs on several PURL resolvers and each of these PURLs has the same associated URL. We hope that common sense and etiquette will prevent most users from creating multiple PURLs on the same resolver, each of which has the same associated URL. Always search the PURL resolver before creating a PURL.