1	Global Identifier Resolution Writ Small 10 April 2006 John Kunze, California Digital Library
2	Overview What is resolution Why we care Why it’s hard How it can be easier Where it can still be improved
3	What is identifier resolution? Resolution is a computation, possibly performed in multiple-stages, that maps an identifier to information associated with it. Examples: Click on id in email, get associated page Enter in browser, get list of format choices Click reference in document, see metadata The id can be of any type: URL, DOI, URN, ISBN, ARK, Handle, etc.
4	What is the result of resolution? Resolution results in access to an associated information object of appropriate type What “the” object is depends on service provider, e.g., a specific representation, a menu of sub-objects, a metadata record, or a 404 Not Found (as result of a completed computation) And it depends on the resolution type, e.g., I2I, I2R, I2C IETF URI WG conceived all such resolution types
5	Why do we care? After all, we can ask Google for anything we want Ambiguous queries, changing services With good resolution (at least to metadata), we get Precise reference to information resources With good resolution to information resources, Actionability (automated access) With good, long-term resolution to resources, Persistent, precise, actionable reference
6	What is a resolver? A resolver is a system that performs one or more stages of the resolution computation, e.g., a web server. Simplest resolver is 1 server, 1 URL:
7	What is a multi-stage resolver? Resolvers often work in multiple stages Each stage is a resolver The “sum” of the stages is a resolver Simplest example: familiar redirection
8	Browser-directed resolution N-stage resolution directed by browser: always with us because of Their Stuff
9	Server-initiated resolution Any resolver stage may initiate back-end stages Like a recursive computation (think DNS) Server-initiated resolution is “horizontal” Simplest two-stage example: web proxy Proxy, as browser target, talks to real target In reverse proxy, id-a real target, not URLa
10	Combined: server-initiated (across), browser-directed (down) resolution
11	URN example: resolver discovery (across), resolver query (down)
12	Handle example: resolver/page discovery (across), resolver query (down)
13	DOI example: Handle-resolver/page discovery (across), resolver query (down)
14	Real life URN/Handle/DOI: browser-based id resolution starts via URL proxy
15	Complex URN/Handle/DOI resolution
16	A simplified identifier resolution plan
17	Concept: global id resolver for persistent, actionable reference Two-stage resolution with only native web tools Back to the future Updates harvested from memory organizations
18	Example global id resolver Pick a stable hostname: Generic: id.archive.org Fast, scalable hash table with Apache rewrite Harvest using sitemaps (e.g, a la google) Examples http://id.archive.org/urn:nbn:se:uu:diva-3324 http://id.archive.org/ark:/13030/tf5p30086k http://id.archive.org/doi:10.1111/j.0307-6946.2004.00571.x
19	Improvements Scaling tests and load balancing alternatives Update synchronization with service changes Security and authenticity checks Multiple resolution