ResourceSync was funded by the Sloan Foundation & JISC A Modular Framework for Web-Based Resource Synchronization Martin Klein Los Alamos National Laboratory

ResourceSync was funded by the Sloan Foundation & JISC

A Modular Framework for Web-Based Resource Synchronization

Martin KleinLos Alamos National Laboratory

@mart1nkle1n

http://www.openarchives.org/rs #resourcesync

Herbert Van de SompelLos Alamos National Laboratory

@hvdsomp

ResourceSync

Herbert Van de Sompel, Martin Klein - ResourceSyncCNI Spring 2014, St. Louis, MO, March 31 2014

ResourceSync

• Collaboration between NISO and the Open Archives Initiative

• Funded by the Sloan Foundation and JISC

• Goal: Devise a specification for web-based resource synchronization


This ResourceSync Presentation

• Problem Domain

• Scope

• Framework - Overview

• Framework – Technology

• Demonstration

• Status


Background - OAI-PMH

• Recurrent metadata exchange from a Data Provider to Service Providers

• XML metadata only

• Repository centric

• Devised 1999-2002, prior to REST, prior to dominance of web search engines


Revisit the Problem Domain - ResourceSync

• Synchronization of resources from a Source to Destinations

• Web resources, anything with an HTTP URI & representation

• Resource centric

• Devised 2012-2013, leverages key ingredients of web interoperability, existing specifications, existing Search Engine Optimization practice


Problem Statement

• Consideration:• Source (server) A has resources that change over time: they

get created, modified, deleted• Destination (servers) X, Y, and Z leverage (some)

resources of Source A

• Problem:• Destinations want to keep in step with the resource changes

at Source A

A Source’s Resources

A Source’s Resources Evolve over Time







Problem Statement

• Consideration:• Source (server) A has resources that change over time: they

get created, modified, deleted• Destination (servers) X, Y, and Z leverage (some)

resources of Source A

• Problem:• Destinations want to keep in step with the resource changes

at Source A

• Goal:• Design an approach for resource synchronization aligned

with the Web Architecture that has a fair chance of adoption by different communities



• Problem Domain

• Scope



• Demonstration

• Status


Scope – Collection Size

• Size of a Source’s resource collection:

• A few resources - small web sites, repositories

• Millions of resources – large repositories, datasets, linked data collections


Scope – Change Frequency

• Change frequency of a Source’s resources:

• Low – daily, weekly, monthly

• High – seconds, minutes


Scope – Synchronization Latency

• Destination’s requirements regarding synchronization latency:

• High latency acceptable

• Low latency essential


Scope – Collection Coverage

• Destination’s requirements regarding the coverage of a Source’s resources:

• Partial coverage of the Source’s resources acceptable

• Full coverage of the Source’s resources verifiable


Scope – Bitstream Accuracy

• Destination’s requirements regarding bitstream accuracy:

• Unverifiable bitstream accuracy acceptable

• Verifiable bitstream coverage essential

One to One Synchronization

One to Many – Master Copy

Many to One - Aggregator

Selective Synchronization

Metadata Harvesting



• Problem Domain

• Scope



• Demonstration

• Status




Solution Perspective - Destination

• Destination needs regarding synchronization:

• Baseline synchronization: Initial catch-up operation to align with the Source’s resources

• Incremental synchronization: Remain synchronized as the Source’s resources evolve

• Audit: Destination determines whether it effectively is in sync with the Source- Bitstream accuracy- Coverage of resources


Solution Perspective - Source

• Source communicates about the state of its resources:

• Publish inventory: snapshot of the state of resources at a moment in time

• Publish changes: enumeration of resource changes that occurred during a temporal interval

• Notify about changes: send notifications as changes occur

• Communication payload:• Minimal, e.g. HTTP URI of resource• Additional, e.g. content-based hash of resource


Resource List

• In order to meet a Destination’s need for baseline synchronization, the Source may publish a Resource List

• A Resource List is an inventory, a snapshot of existing resources

• Per resource, it minimally provides the resource’s URI

• Process:- Destination obtains the Resource List- Destination obtains listed resources by their URI- Optimization: Resource Dump, a list pointing to ZIP files

that contain resource representations

Publish Resource List: Inventory at Tx

Resource List @Tx = { A ; B ; C }


Change List

• In order to meet a Destination’s need for incremental synchronization, the Source may publish a Change List

• A Change List enumerates resource change events that occurred in a temporal interval

• For each event, it minimally lists datetime, URI of the resource, the nature of the change

• Process:- Destination obtains the Change List- Destination obtains created/updated resources, removes

deleted resources- Optimization: Change Dump

Publish Change List: Resource Changes During Interval Ty-Tz

Change List [Ty,Tz] = { A updated @Tc ; B updated @Tc ; C created @Td ; D deleted @Te ; C updated @Tf }


Change Notification

• In order to meet a Destination’s need for incremental synchronization and low latency, the Source may send Change Notifications

• A Change Notification conveys resource change events as they occur

• For each event, it minimally lists datetime, URI of the resource, the nature of the change

- Process:- Destination receives Change Notification- Destination obtains created/updated resources, removes

deleted resources


Send Change Notification – Resource Changes at Ta

Change Notification @Ta = { A updated @Ta }


Send Change Notification – Resource Changes at Tb

Change Notification @Tb = { D updated @Tb }


Send Change Notification – Resource Changes at Tc

Change Notification @Tc = { A updated @Tc ; B updated @Tc }


Send Change Notification – Resource Changes at Td

Change Notification @Td = { C created @Td }


Send Change Notification – Resource Changes at Te

Change Notification @Te = { D deleted @Te }


Send Change Notification – Resource Changes at Tf

Change Notification @Tf = { C updated @Tf }


Communication Payload – Metadata & Links

• A Source may provide additional metadata and links pertaining to resources conveyed in Resource Lists, Change Lists, Change Notifications

• Metadata about a resource: content encoding, content length, mime type, content-based hash

• Linking to related resources: mirror copies, alternate representations, resource versions, diff between current and previous version, metadata-to-content link, content-to-metadata link, collection membership, etc.


Communication Payload – Metadata – Hash

• In order to meet a Destination’s need for audit, the Source may provide a content-based hash pertaining to a resource

• Source computes the content-based hash for a resource

• Source provides the hash as metadata pertaining to the resource in its communication payload

• Destination processes communication payload, obtains the resource

• Destination computes the content-based hash for the obtained resource, compares with the Source’s


Communication Payload – Link – Interlink Metadata & Content

• In order to allow a Destination to establish the relationship between a Source’s metadata and a Source’s content, the Source may provide appropriate links

• Metadata resources and content resources are just resources identified by HTTP URIs

• Both can independently be subject to synchronization and can be interlinked using appropriately typed links


Communication Payload – Link – Link to Diff

• In order to minimize content transfer, a Source may link to a diff between the previous and the new version of a resource

• Destination can obtain the diff and patch its (previous) version of the resource

• Connection between the resource and the diff is established by means of appropriately typed link

• Nature of the diff is established by means of MIME type- Few diff MIME types exist. Communities can establish

their own.


Further Framework Characteristics

• Modular: A Source does not have to implement all capabilities

• Source decides which capabilities to support based on local and community requirements

• Sets of Resources: Division of a Source’s resource collection in logical groupings.

• Supported capabilities can differ per set

• Discovery: Mechanisms for Destinations to determine whether and how a Source supports ResourceSync

• Based on conventions for web discovery and documents that detail the level of support



• Problem Domain

• Scope



• Demonstration

• Status


Sitemap Protocol

• ResourceSync builds on the Sitemap protocol used by major search engines

• Similarity between resource synchronization and resource discovery/indexing

• Extends the Sitemap protocol to meet synchronization needs• Cf. Metadata and Links

• Sitemap document format is used throughout the framework to express Resource Lists, Change Lists, etc.• Type of ResourceSync document can be determined

through explicit declaration


Common Sitemap

<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9”>

<url> <loc>http://example.com/res1</loc> <lastmod>2013-01-02T13:00:00Z</lastmod> </url>

<url> <loc>http://example.com/res2</loc> <lastmod>2013-01-02T14:00:00Z</lastmod> </url> …</urlset>


Resource List

<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:rs="http://www.openarchives.org/rs/terms/"> <rs:md capability="resourcelist" at="2013-01-03T09:00:00Z” /> <url> <loc>http://example.com/res1</loc> <lastmod>2013-01-02T13:00:00Z</lastmod> <rs:md hash="md5:1584abdf8ebdc9802ac0c6a7402c03b6" length="8876" type=”application/pdf” /> </url> <url> … </url></urlset>


Change List

<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:rs="http://www.openarchives.org/rs/terms/"> <rs:md capability=”changelist" from="2013-01-02T09:00:00Z” until="2013-01-03T09:00:00Z” /> <url> <loc>http://example.com/res2</loc> <lastmod>2013-01-02T13:00:00Z</lastmod> <rs:md change=”updated” /> <rs:ln href=“http://example.com/res2/meta” rel=“describedby” /> </url> <url> … </url></urlset>


Change Notification

<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:rs="http://www.openarchives.org/rs/terms/"><url> <loc>http://example.com/res3</loc> <lastmod>2013-01-02T13:00:00Z</lastmod> <rs:md change=”updated” type=”application/json” /> <rs:ln href=“http://example.com/res3/diff” rel=“http://www.openarchives.org/rs/terms/patch” type=“application/json-patch”/> </url> <url> … </url></urlset>


PubSubHubbub Protocol

• ResourceSync builds on the PuSH protocol used for syndication of Atom/RSS feeds

• Introduces a novel use for pushing change notifications from a Source to subscribing Destinations

• Destinations subscribe to a Source’s change notifications via a Hub

• The Source pushes change notifications out to the Hub

• The Hub relays change notifications from the Source to the subscribing Destinations

Destination Discovers Source’s Notification Channel & Hub

Destination Subscribes to Source’s Notification Channel

Source Sends Change Notification to Hub

Hub Relays Change Notification to Destination(s)



• Problem Domain

• Scope

• Example Use Cases

• Framework Characteristics

• Demonstration

• Status

Source Sends Change Notifications

Destination Acts Upon Change Notifications

Observe the State of Source and Destination



• Problem Domain

• Scope

• Example Use Cases

• Framework Characteristics

• Demonstration

• Status


Status of Specifications

• ResourceSync Core Specification currently in NISO Voting Pool• Ends April 16 2014• Please vote if you are a NISO member• If vote is positive should be ANISO/NISO Z39.99 by July 2014• Spec on OAI web site fully aligned with NISO Standard

• ResourceSync Notification Specification currently in beta• Ongoing tests with PubSubHubbub• Hub, Source, Destination Python software to be released • Public Hub for testing will be made available

• ResourceSync Archive Specification currently in beta


Pointers

• Specification

http://www.openarchives.org/rs/http://www.openarchives.org/rs/resourcesynchttp://www.openarchives.org/rs/notificationhttp://www.openarchives.org/rs/archives

• List for public comment

https://groups.google.com/d/forum/resourcesync

• Building blocks

http://sitemaps.orghttps://code.google.com/p/pubsubhubbub/


Papers

• Klein, M., and Van de Sompel, H. (2013) Extending Sitemaps for Resourcesync. http://arxiv.org/abs/1305.4890 ACM/IEEE JCDL 2013

• Haslhofer, B., Warner, S, Lagoze, C., Klein, M., Sanderson, R., Nelson, M.L. and Van de Sompel, H. (2013) ResourceSync: Leveraging Sitemaps for Resource Synchronization. http://arxiv.org/abs/1305.1476 WWW 2013 Developer Track

• Klein, M., Sanderson, R., Van de Sompel, H., Warner, S, Haslhofer, B., Lagoze, C., and Nelson, M.L. (2013) A Technical Framework for Resource Synchronization. http://dx.doi.org/10.1045/january2013-klein D-Lib Magazine.

• Van de Sompel, H., Sanderson, R., Klein, M., Nelson, M.L., Haslhofer, B., Warner, S, and Lagoze, C. (2012) A Perspective on Resource Synchronization. http://dx.doi.org/10.1045/september2012-vandesompel D-Lib Magazine.

http://arxiv.org/abs/1305.4890

http://arxiv.org/abs/1305.1476

http://dx.doi.org/10.1045/january2013-klein

http://dx.doi.org/10.1045/september2012-vandesompel


Acknowledgments

• Editors: Martin Klein, Robert Sanderson, Herbert Van de Sompel (Los Alamos National Laboratory), Simeon Warner (Cornell University), Graham Klyne ( University of Oxford), Bernhard Haslhofer (University of Vienna), Michael L. Nelson (Old Dominion University), Carl Lagoze ( University of Michigan)

• Contributors: Peter Murray (Lyrasis), Todd Carpenter, Nettie Lagace (NISO), Richard Jones (Cottage Labs), Stuart Lewis (University of Edinburgh), Paul Walk (University of Edinburgh), Jeff Young (OCLC), Shlomo Sanders (Ex Libris), Kevin Ford (Library of Congress)

• Demonstration: Martin Klein, Harihar Shankar, Herbert Van de Sompel (Los Alamos National Laboratory)

ResourceSync was funded by the Sloan Foundation & JISC

A Modular Framework for Web-Based Resource Synchronization

Martin KleinLos Alamos National Laboratory

@mart1nkle1n

http://www.openarchives.org/rs #resourcesync

Herbert Van de SompelLos Alamos National Laboratory

@hvdsomp

ResourceSync

Documents

ResourceSync was funded by the Sloan Foundation & JISC A Modular Framework for Web-Based Resource Synchronization Martin Klein Los Alamos National Laboratory