Internet DRAFT - draft-kahn-dsii-id-res-sys
draft-kahn-dsii-id-res-sys
INTERNET-DRAFT R. Kahn
IETF Stream CNRI
Intended Status: Informational A. Maffei
WHOI
Expires: 26 December 2012 24 June 2012
Terminology and Use Cases for Interoperability of
Identifier Resolution Systems
draft-kahn-dsii-id-res-sys-00
Abstract
Identifier Systems have been in existence for many years and are in
widespread use. An opaque identifier conveys essentially nothing
about the information identified and must be converted into useful
intermediate information, known as state information, before the
information being identified can be accessed or used. An identifier
that is can be processed by a system in the Internet to provide
useful and actionable intermediate state information is said to be
resolvable. Although there is ongoing discussion about the value of
opaque versus non-opaque identifiers, we assume the existence of a
minimal syntax structure for the identifier and also that the
resolution mechanisms only knows about the minimal syntax of the
identifier. In this document we introduce the notion of
interoperability of identifier resolution systems as a key component
for enabling interoperability of heterogeneous information systems
more broadly, and discuss the role of unique persistent resolvable
identifiers. Terminology is proposed to facilitate this discussion
and a set of use cases demonstrating the need for interoperability of
resolution systems are included.
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1. Introduction
Identifier Systems have been in existence for many years and are in
widespread use in society. They range from the simplest systems of
enumeration to more complex means of conveying information about the
things, values, services, or other identified items. Opaque
identifiers, such as strings from cryptographic hash functions,
convey essentially nothing about the information identified and must
be resolved before they can be used in a digital environment. An
identifier that can be processed by a system in the Internet to
provide useful and actionable state information is said to be
resolvable. In this document, we focus on resolvable identifiers and
the resolution systems that support them. Specifically, we introduce
the notion of interoperability of resolution systems and discuss the
notion of unique persistent resolvable identifiers along with a
common terminology for discussing these systems. This capability has
been implemented as part of the Digital Object Architecture [1].
Finally, a set of selected use cases that support this notion is also
provided.
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2. Definitions
Identifier
While some systems of identification have used names and semantics
to identify a variety of things, many other systems have used
combinations of syntax and semantics. In this document we assume
no semantics are available in the identifier and only enough
syntax for the resolution system to understand how to resolve it.
Identifier Generation Rules
These rules specify how to create a well-formed identifier for use
within a resolution system. Normally, the rules will consist of
syntax constraints, but may go beyond that, as in requiring that
some or all of an identifier be generated in a specific manner.
Identifierspace
This refers to the set of identifiers that are generated using the
rules.
Digital Object
A digital object consists of structured data in the form of a bit
sequence or a set of bit sequences that can be interpreted by a
computer or other computational facility. Each sequence consists
of a type-value pair, at least one of which is the associated
unique persistent identifier for the digital object. A digital
object may incorporate separately identifiable digital objects or
only the identifiers for those objects or a combination of the
two. The digital objects need not all be stored in one place, or
stored at all, but if they are stored, they are generally assumed
to be accessible from the one or more known locations in the
Internet. Indeed some digital objects may constitute mobile
programs that given specific tasks to perform in the Internet, and
would interact with other programs, registries, repositories or
information resources structured as digital objects in order to
carry out its assigned tasks.
Resolution System
A system in the Internet that accepts an identifier as input and
produces useful and actionable "state information" such that, for
example, the digital object associated with that identifier may be
accessed and used. This state information is intended to inform
the user or the user's system as to specific actions to take,
restrictions on actions and associated information such as a means
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of authentication, public keys, and whether certain actions will
incur costs or require allocation of significant resources such as
storage. It is assumed that many different resolution systems may
exist in the Internet. Each such system may have its own
identifier rules and produce information in different ways.
Uniqueness
An identifier is said to be unique at a given time with respect to
a given resolution system if there is only one authorized set of
useful and actionable information held by the resolution system
for that identifier, and that information is produced by a
resolution request with that identifier.
Persistence
An identifier is said to be persistent if its associated
resolution system can be relied upon to return useful and
actionable state information about the identified digital object
over a period of time that is at least as long as the digital
object exists and in the face of changes to the digital object,
such as ownership and location, without the identifier itself
changing. The period of time may vary somewhat depending on the
domain of use. For example, the identifier may outlast the
identified digital object, such that a reference to it using the
identifier can be resolved to useful and actionable state
information even when the digital object is no longer available.
The quality of persistence is dependent on a combination of social
and business infrastructure, e.g., an organization assuming
responsibility for maintaining the resolution information and
underlying resolution system and technology.
Immutability
The term immutable refers to a digital object and its associated
identifier that is fixed and does not change. Other than the
digital object identifier, however, other aspects of the digital
object metadata may change over time as, for example, the object
is moved from place to place, as long as the basic structured
information that comprises the digital object does not change over
time.
Mutability
This term refers to a digital object that is not immutable.
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Structured Data and Metadata
Normally, a resolution request leads to one of two basic results.
One result is obtaining structured data in digital form that
represents a service, resource or other information represented in
digital form such as a document, bill of lading, or movie. The
other result is obtaining metadata about the service, resource, or
information. In this document, we focus on metadata that is used
for rapid reaction by the user's system, as in clicking an
identifier to find the location(s) of the item, or even the
location of the systems to provide parts of the metadata. More
general forms of metadata, such as might typically be used in a
search system, would not be provided by the resolution system;
rather, the user could be referred to a more substantive registry
of such information with advanced browsing and searching
capabilities.
3. Use cases for Actionable Identifier Resolver Interoperability
Interoperable Proxying
Let us assume a user of resolution system A needs to resolve an
identifier known only to resolution system B. We assume the user
does not have the software needed to use resolution system B, or
else the user might try to resolve the identifier directly from
resolution system B. Rather, the user asks resolution system A to
do the resolution and system A takes on the responsibility to ask
resolution system B. These two resolution systems are
interoperable if a resolution request sent from resolution system
A to resolution system B will succeed in producing the information
in a form usable by the party who requested it. Typically, this
will require a kind of service level agreement (SLA) between the
two resolution system administrators to share information about
how they store and otherwise manage resolution information in
order to produce a useful response to the user, and also to agree
on what various fields mean in order to do an effective
translation into the terms of the asking resolution system.
This document does not address how such SLAs should be structured
or how any resolution system should operate internally. Most
likely, only a small number of resolution systems will be
desirable for handling the bulk of identifier resolution
requirements. A list of such systems could be made available in
the Internet, if desired.
Each resolution system may have its own means of providing
security, but this document does not address how security may be
achieved for the overall interoperable proxy service.
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Distributed replica management
Retention and caching decisions depend on the status of replicas
of digital objects managed by multiple, distributed services.
Duplicates may, in principle, have different identifiers in
different systems. In order to query or harvest the status of
these digital objects, to make retention or migration decisions
(e.g., deduplication, or migrating a digital object which a
service is about to drop), it might be necessary to resolve
multiple identifiers against multiple resolution services.
Provenance tracking
In a complex distributed workflow, source data and related data
services may be managed separately, perhaps via heterogeneous
systems that rely on different identifier systems. In order to
reason over provenance it may be necessary to access these objects
or their metadata.
Data fusion
In this case a digital object is assembled from component digital
objects, which may not all be accessible via the same service or
within the same identifierspace; as a result, the identifiers may
not all be resolvable in the same identifierspace and the assembly
process would require resolving each identifier separately.
Harvesting and spidering
In this case, which is similar to the data fusion case, an agent
fetches a digital object which contains references to other
digital objects and then needs to be able to resolve those
references recursively.
4. Security Considerations
<This section purposely left blank in this version.>
5. IANA Considerations
No IANA actions are needed.
6. Informational References
[1] Corporation for National Research Initiatives, "A brief overview
of the Digital Object Architecture", 1 June 2010.
<http://cnri.reston.va.us/papers/
OverviewDigitalObjectArchitecture.pdf>
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Authors' Addresses
Robert Kahn
Corporation for National Research Initiatives
1895 Preston White Drive, Suite 100
Reston, VA 20191
USA
EMail: rkahn@cnri.reston.va.us
Andrew Maffei
Woods Hole Oceanographic Institution
Mailstop 44
Woods Hole, MA 02543
USA
EMail: amaffei@whoi.edu
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