Handle System

The Handle System is defined in informational RFCs 3650,^[1] 3651^[6] and 3652^[7] of the Internet Engineering Task Force (IETF); it includes an open set of protocols, a namespace, and a reference implementation of the protocols. Documentation, software, and related information is provided by CNRI on a dedicated website^[8]


Handles consist of a prefix which identifies a "naming authority" and a suffix which gives the "local name" of a resource. Similar to domain names, prefixes are issued to naming authorities by one of the "multi-primary administrators" of the system upon payment of a fee, which must be renewed annually. A naming authority may create any number of handles, with unique "local names", within their assigned prefixes. An example of a handle is:


In the first example, which is the handle for the HANDLE.NET software license, 20.1000 is the prefix assigned to the naming authority (in this case, Handle.net itself) and 100 is the local name within that namespace. The local name may consist of any characters from the Unicode UCS-2 character set. The prefix also consists of any UCS-2 characters, other than "/". The prefixes consist of one or more naming authority segments, separated by periods, representing a hierarchy of naming authorities. Thus, in the example 20 is the naming authority prefix for CNRI, while 1000 designates a subordinate naming authority within the 20 prefix. Other examples of top-level prefixes for the federated naming authorities of the DONA Foundation are 10 for DOI handles; 11 for handles assigned by the ITU; 21 for handles issued by the German Gesellschaft für wissenschaftliche Datenverarbeitung mbH Göttingen (GWDG), the scientific computing center of the University of Göttingen; and 86 for the Coalition of Handle Services – China. Older "legacy" prefixes issued by CNRI before the "multi-primary administrator" (MPA) structure was instituted are typically four of five digits, as in the second example above, a handle administered by the University of Leicester. All prefixes must be registered in the Global Handle Registry through an DONA Foundation approved registrar, normally for a fee.


As with other uses of handles in computing, the handle is opaque; that is, it encodes no information about the underlying resource and provides only the means to retrieve metadata about the resource.


This may be contrasted with a Uniform Resource Locator (URL), which may encode within the identifier such attributes of the resource as the protocol to be used to access the server holding the resource, the server host name and port number, and perhaps even location specifics such as the name of a file in the server file system containing the resource. In the Handle System, these specifics are not encoded in the handle, but are found in the metadata to which the handle is bound.


The metadata may include many attributes of the information resource, such as its locations, the forms in which it is available, the types of access (e.g. "free" versus "paid") offered, and to whom. The processing of the metadata to determine how and where the resource should be accessed, and the provision of the resource to the user, are performed in a separate step, called "resolution", using a Resolver, a server which may be different from the ones involved in exchanging the handle for the metadata. Unlike URLs, which may become invalid if the metadata embedded within them becomes invalid, handles do not become invalid and do not need to change when locations or other metadata attributes change. This helps to prevent link rot, as changes in the information resource (such as location) need only be reflected in changes to the metadata, rather than in changes in every reference to the resource.


Each handle may have its own administrator and administration of the handles can be done in a distributed environment, similar to DNS domain names. The name-to-value bindings may also be secured, both via signatures to verify the data and via challenge response to verify the transmission of the data, allowing handles to be used in trust management applications.


It is possible for the same underlying information resource to be associated with multiple handles, as when two university libraries generate handles (and therefore possibly different sets of metadata) for the same book.


The Handle System is compatible with the Domain Name System (DNS), but does not require it, unlike persistent identifiers such as PURLs or ARKs, which are similar to handles, but which utilise domain names. However, unlike these domain-name based approaches, handles do require a separate prefix registration process and handle servers separate from the domain name servers.


Handles can be used natively, or expressed as Uniform Resource Identifiers (URIs) through a namespace within the info URI scheme;^[9][10] for example, 20.1000/100 may be written as the URI, info:hdl/20.1000/100. Some Handle System namespaces, such as Digital Object Identifiers, are "info:" URI namespaces in their own right; for example, info:doi/10.1000/182 is another way of writing the handle for the current revision of the DOI Handbook^[11] as a URI.


Some Handle System namespaces define special presentation rules. For example, Digital Object Identifiers, which represent a high percentage of the extant handles, are usually presented with a "doi:" prefix: doi:10.1000/182.


Any Handle may be expressed as a Uniform Resource Locator (URL) through the use of the generic HTTP proxy server,:^[12]


Some Handle-based systems offer an HTTP proxy server that is intended for use with their own system such as:

Implementation[edit]

Implementation of the Handle System consists of Local Handle Services, each of which is made up of one or more sites that provide the servers that store specific handles. The Global Handle Registry is a unique Local Handle Service which stores information on the prefixes (also known as naming authorities) within the Handle System and can be queried to find out where specific handles are stored on other Local Handle Services within this distributed system.


The Handle System website provides a series of implementation tools, notably the HANDLE.NET Software^[13] and HANDLE.NET Client Libraries.^[14] Handle clients can be embedded in end user software (e.g., a web browser) or in server software (e.g., a web server) and extensions are already available for Adobe Acrobat^[15] and Firefox.^[16]


Handle client software libraries are available in both C and Java. Some applications have developed specific add-on tools, e.g., for the DOI System.^[17]


The interoperable network of distributed handle resolver servers (also known as the Proxy Server System) are linked through a Global Resolver (which is one logical entity though physically decentralised and mirrored). Users of Handle System technology obtain a handle prefix created in the Global Handle Registry. The Global Handle Registry maintains and resolves the prefixes of locally maintained handle services. Any local handle service can, therefore, resolve any handle through the Global Resolver.


Handles (identifiers) are passed by a client, as a query of the naming authority/prefix, to the Handle System's Global Handle Registry (GHR). The GHR responds by sending the client the location information for the relevant Local Handle Service (which may consist of multiple servers in multiple sites); a query is then sent to the relevant server within the Local Handle Service. The Local Handle Service returns the information needed to acquire the resource, e.g., a URL which can then be turned into an HTTP re-direct. (Note: if the client already has information on the appropriate LHS to query, the initial query to GHR is omitted)


Though the original model from which the Handle System derives dealt with management of digital objects, the Handle System does not mandate any particular model of relationships between the identified entities, nor is it limited to identifying only digital objects: non-digital entities may be represented as a corresponding digital object for the purposes of digital object management. Some care is needed in the definition of such objects and how they relate to non-digital entities; there are established models that can aid in such definitions e.g., Functional Requirements for Bibliographic Records (FRBR), CIDOC CRM, and indecs content model. Some applications have found it helpful to marry such a framework to the handle application: for example, the Advanced Distributed Learning (ADL) Initiative^[18] brings together Handle System application with existing standards for distributed learning content, using a Shareable Content Object Reference Model (SCORM),^[19] and the Digital Object Identifier (DOI) system implementation of the Handle System has adopted it together with the indecs framework to deal with semantic interoperability.


The Handle System also makes explicit the importance of organizational commitment to a persistent identifier scheme, but does not mandate one model for ensuring such commitment. Individual applications may choose to establish their own sets of rules and social infrastructure to ensure persistence (e.g., when used in the DSpace application, and the DOI application).^[20]

Licences and use policy[edit]

Handle System, HANDLE.NET and Global Handle Registry are trademarks of the Corporation for National Research Initiatives (CNRI), a non-profit research and development corporation in the US. The Handle System is the subject of patents by CNRI, which licenses its Handle System technology through a public license,^[24] similar to an open source license, in order to enable broader use of the technology. Handle System infrastructure is supported by prefix registration and service fees, with the majority coming from single prefix holders. The largest current single contributor is the International DOI Foundation. The Public License allows commercial and non-commercial use at low cost of both its patented technology and the reference implementation of the software, and allows the software to be freely embedded in other systems and products. A Service Agreement^[5] is also available for users who intend to provide identifier and/or resolution services using the Handle System technology under the Handle System public license.