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RFC 1728
Network Working Group C. Weider
Request for Comments: 1728 Bunyip Information Systems
Category: Informational December 1994
Resource Transponders
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
Abstract
Although a number of systems have been created in the last several
years to provide resource location and navigation on the Internet,
the information contained in these systems must be maintained and
updated by hand. This paper describes an automatic mechanism, the
resource transponder, for maintaining resource location information.
Author's Note:
This document is being circulated as sort of a research paper;
consequently there are no protocol specifications or anything of the
sort. I hope that we can go from here and actually design them if
there's consensus that they are potentially useful. Once we have some
idea of the required functionality, we can then go out and
standardize them.
Disclaimer
This paper represents only the opinions of the author; it does not
represent the consensus of the IIIR Working Group, although it is
recognized by them as one legitimate approach to a solution of the
problem.
1. Introduction
In the past few years, we've seen the invention and growth of a
number of information location systems on the Internet, e.g., archie,
Gopher, and WAIS. However, as these systems have become widely
deployed, a number of maintenance and security problems have arisen
with them. Some of the major ones:
1) Out of necessity, most of these systems contain pointers to the
desired resources rather than the resources themselves. Therefore,
if a resource becomes obsolete, is modified, or is moved, the
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RFC 1728 Resource Transponders December 1994
location system must be updated by hand. Some systems (archie in
particular) proactively create updated indexes by contacting every
resource on a certain time schedule (every 30 days or so) but this
means that the system can be up to 30 days out of date, and this
process can be highly inefficient depending on the percentage of
information that has changed.
2) Conversely, anyone who maintains a resource that they wish indexed
must keep track of every directory which contains a pointer to
that resource, so that if it is modified, all the directories can
be updated. This obviously is an optimistic scenario.
3) Many organizations which have installed these systems do not have
the the available resources or expertise to maintain the
information in the systems. Thus we have long periods where the
information drifts, then a short period when the information is
updated again.
4) Even though these systems are almost always out of date today,
this problem will become increasingly harder for humans to manage
by hand as everyone on the net becomes their own publisher. Also,
as the net speeds up and people rely more and more on accurate
information, human-induced delays in updates of these systems will
become increasingly intolerable.
5) Most, if not all, of these systems provide no security whatsoever;
if a pointer to a resource appears in a locator system, then it is
assumed to be meant for public consumption. There are many
potential information providers who would like to use publicly
deployed information systems to publish to a very selected
clientele, and do not wish to allow the whole net access to their
resources.
2. Requirements for a Solution
There are several objectives which must be met by any proposed
solution to these problems:
1) We need to decrease the personnel resources needed for indexing
and pointer maintenance.
2) We need to increase the reliability and accuracy of the
information held in resource location systems.
3) We need to provide some mechanisms for security, particularly by
mediating access to the resources.
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RFC 1728 Resource Transponders December 1994
4) We need to make it easy for non-experts, such as librarians,
archivists, and database maintainers, to announce their new
resources to the various resource location services.
Many of these problems can be solved by a 'resource transponder'
mechanism.
3. Resource Transponders
The resource transponder system works by adding two new layers to
every resource: metainformation and an agent to update a resource
location system (RLS) with that metainformation. The metainformation
layer is physically attached to every resource, so that when the
resource is moved or altered, the metainformation is immediately
available to update the RLS. The agent layer may also be attached to
the resource or may not be; the implications of both of these options
are discussed in detail below.
3.1 Metainformation
The metainformation layer of a given resource contains any
information which might be required to create a pointer to this
resource, and any information which may be useful for indicating how
to catalog or index the resource. For example, the metainformation
layer of a text document might contain such things as the Uniform
Resource Name (URN) of the document (this is sort of a ISBN number
for electronic resources), the title of the document, a Uniform
Resource Locator (URL) for the document (this is a combination net
address and access method indicator, used for retrieval), the size of
the document, etc. Thus the metainformation layer contains data about
the resource to which it is attached.
This metainformation is expected to be modifiable. For example, the
metainformation layer may contain a history of where this particular
copy of a resource has been. Let's say that a resource/transponder
pair has been moved. When it gets to its new location, the agent can
then attempt to contact the resource at its old location to determine
whether the resource is still there (in which case the agent will
simply cause the new location to be added to the RLS) or whether the
resource is not there (in which case the agent can tell the RLS to
add the current pointer and delete the old one).
A number of other possibilities for the contents of the
metainformation level are contained in section 4.1.
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RFC 1728 Resource Transponders December 1994
3.2 Agents
The agent layer of a given resource contains an executable program
which is responsible for reading the metainformation attached to the
resource and using that information to update a RLS. It is also
responsible for updating the metainformation where necessary and for
running any indexing programs required by the RLS it is attempting to
update.
When the tools required to build agents are constructed and deployed,
the author expects the agents to begin mediating access to the
resource, particularly for agents attached to resources which are not
currently considered active processes, such as text files and
digitized images. In this futuristic model, someone wishing to read
a given document would have to first negotiate access to the data
with the agent; the agent would then be responsible for delivering
the data to the client. However, it is expected that this type of
agent will not be widely deployed for some time.
Different ways of implementing agents are discussed in section 4.2.
4. Models for implementations of resource transponders
4.1. Models for implementations of the metainformation layer
The metainformation layer can be impelemented in a number of ways,
depending on the resource with which it is associated. For an
'active' resource, such as an on-line catalog or a mail-based
service, the metainformation can be stored in a file with a well-
known name in the software distribution. Alternatively, the
metainformation could be stored as a record in the data which the
resource serves. For a text document, the metainformation could be
stored as the first or last N bytes of the document (which would
break a number of editors and file display techniques, but would
guarantee that the metainformation is moved with the resource), or
perhaps as a file with a logically associated name (paper2.meta
associated with paper2.txt, for example). The problem with this
second approach is that the user must know that they have to move the
metainformation with the file itself, or things will start breaking.
If an agent is explicitly attached to the resource, the agent could
contain the metainformation internally.
In any case, the resource transponder system must be able to
guarantee that the metainformation is moved when the resource is
moved.
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RFC 1728 Resource Transponders December 1994
4.2 Models for implementations of the agents
The agent layer can also be implemented in a number of ways,
depending on such things as system loads, desired sizes of resources,
multitasking capabilities, etc.
The easiest and for many unitasking systems the cleanest way of
implementing an agent is to have one agent per computer. Then when a
resource is moved onto that computer, the agent is explicitly
activated and notified where the new resource is. For example, let's
say that someone wishes to download a copy of a resource and then let
the RLS know that that resource is available for public consumption.
She would download the resource and then run the agent, which would
then notify the RLS and update the metainformation attached to the
resource. This model could also be used to track files on a LAN, or
to provide local location services with no need to run a larger RLS.
Another model for implementation of the agent is to have one agent
per resource. In this model, the agent would be moved along with the
resource and the metainformation. The agent could be implemented in a
file which would be associated with the resource; in that case the
agent would have to be explicitly activated when the resource was
moved. Alternatively, the agent/metainformation/resource system could
be implemented as one system, or in one file. In this case, the agent
itself would always be active, and would be responsible for mediating
access to the resource. When one did a 'telnet' to a resource with
an active agent, the agent would accept the telnet connection and be
responsible for providing security and translation for the data. This
could provide great security for resources while still allowing
pointers to them to be placed in public RLS's; the data in the
resource could be encrypted, with the agent responsible for
decrypting it.
5. Security Considerations
Security issues are discussed throughout this memo.
6. Author's Address
Chris Weider
Bunyip Information Systems, Inc.
2001 S. Huron Parkway, #12
Ann Arbor, MI 48104
USA
Phone: +1 313-971-2223
Fax: +1 313-971-2223
EMail: clw@bunyip.com
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