Metadata Harvesting

1. Metadata Harvesting Interoperable digital collections

2. Distributed libraries • The reality in most digital libraries is that no one location has all the materials that may be of interest. • It is often more efficient to allow a number of sites each to retain some of the materials. • How can we assure clients that they will see all relevant resources, regardless of which library they search?

3. Two basic approaches • One service provider with access to resources stored in multiple locations • Information about all the resources located at the service provider. • Services (DL scenarios) use the information to provide connections to resources at multiple locations • Distributed services • Information kept with the resources • Services, local to each collection, interact with other collection sites

4. Two protocols • Z39.50 • Developed before the web • Protocol for communicating with collection holders in order to provide services. • Open Archives Initiative • Relatively recent innovation • Central service provider gathers information from collection holders

5. Z39.50 - briefly • Information Retrieval Service Definition and Protocol Specifications for Library Applications • Initially developed over the OSI network standards • Protocol for information exchange • Free the information seeker from the need to know the details of the target database configuration • Each site provides services • Each service queries remote sites for needed information • Information requests mapped to database queries at the collection site. • Some inconsistency in the interpretation of queries.

6. Distributed ResourcesMultiple Services Approach 1 - One service provider gathers information about data and uses it to provide services Data provider Data provider Data provider Service provider -- search, browse, compare, etc. Data provider Data provider

7. Distributed data and services Search, browse Approach 2: Each system is both a data repository and a service provider. Services query other data providers as needed. Search, browse, compare

8. Hybrid systems Each server likely to have its own clients. Difference is whether the information exchange is periodic or ad hoc Data provider Data provider Data provider Service provider -- search, browse, compare, etc. Data provider Data provider

9. Open Archives Initiative (OAI) • Web-based • Uses HTTP to communicate between sites • Centralized server • Services provided from a site that has already gathered the information it needs for those services from a distributed collection of sites.

10. OAI PMH • Interoperability through Metadata Exchange • The Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH) is a low-barrier mechanism for repository interoperability. Data Providers are repositories that expose structured metadata via OAI-PMH. Service Providers then make OAI-PMH service requests to harvest that metadata. OAI-PMH is a set of six verbs or services that are invoked within HTTP. http://www.openarchives.org/pmh/

11. OAI - ORE • Aggregations of Web Resources • Open Archives Initiative Object Reuse and Exchange (OAI-ORE) defines standards for the description and exchange of aggregations of Web resources. These aggregations, sometimes called compound digital objects, may combine distributed resources with multiple media types including text, images, data, and video. The goal of these standards is to expose the rich content in these aggregations to applications that support authoring, deposit, exchange, visualization, reuse, and preservation. Although a motivating use case for the work is the changing nature of scholarship and scholarly communication, and the need for cyberinfrastructure to support that scholarship, the intent of the effort is to develop standards that generalize across all web-based information including the increasing popular social networks of “web 2.0”. http://www.openarchives.org/ore/

12. OAI-ORE example • The URI http://arxiv.org/abs/astro-ph/0601007 of the human start page. • The formats in which the document is available, i.e. PostScript, PDF, etc. These are effectively the constituents of the aggregation that is the arXiv document. For the remainder of this example we will consider this human start page, the splash page, as also a constituent of the aggregation • The title of the arXiv document. • The authors of the arXiv document. • The creation and last modification date of the arXiv document. • Identifiers of entities that are in some manner comparable to this arXiv document. For example, a version of this document was later published as an article in a peer-reviewed journal, and the Digital Object Identifier of that article is shown. • The versions of this document. • Links to other arXiv documents in the same collection (i.e., astro-ph). • Citations made by this arXiv document, and citations it received from other documents. The problem is that this URI does not really represent the resource, although this is the human readable landing page. http://www.openarchives.org/ore/1.0/primer

13. OAI - ORE http://www.openarchives.org/ore/1.0/primer.html#Example • ORE allows aggregation of related web pages to form a logical unit • The representation allows access to all of the components of a resource at once.

14. Our focus • We will concentrate on OAI – PMH • Allowing us to know about other resources of interest to our societies • Allowing others to know about the resources we have available

15. Spot check • What sort of resources are handled by your site? Are the resources well represented by the landing page? Do you have complex resources that need structural description as well as the usual Dublin Core fields? • Spend a few minutes talking to someone not on your team about the resources you have and what it takes to describe them. Then switch and listen to the other person’s analysis of their resources. • Report your conclusions

16. Older approaches - 1 • Z39.50 • Special purpose protocol (machine to machine, not web interface) • Gathers information when it is requested, not on a scheduled basis.

17. OAI Compared to Z39.50 Source: oai.grainger.uiuc.edu/FinalReport/JCDL_2003_OAI_Intro.ppt

18. Open Archives Initiative Protocol for Metadata Harvesting -- OAI-PMH Implemented as CGI, ASP, PHP, or other Repository Harvester OAI PMH defines an interface between the Harvester and any number of Repositories HTTP req (OAI verb) OAI OAI HTTP resp (XML) Metadata Provider Service Provider Any system may serve as a harvester, repository, or both

19. OAI - PMH components Service Providersand Data Providers Requests and Responses http://www.oaforum.org/tutorial/english/page3.htm#section3

20. Records • Metadata of a resource. • Three parts • Header (required) • Identifier (required: 1 only) • Datestamp (required: 1 only) • setSpec elements (optional: 0, 1, or more) • Status attribute for deleted item • Metadata (required) • XML encoded metadata with root tag, namespace • Repositories must support Dublin Core, other formats optional • “About” statement (optional) • Right statements • Provenance statements

21. Identifiers • Globally unique identifier • Valid URI • Examples • oai:<archiveId>:<recordId> • oai:etd.vt.edu:etd-1234567890 • Must resolve to one item • No duplicates • No reuse of previously used identifiers

22. Datestamps • Date of last modification of a record • Used only for harvesting (meta metadata?) • Mandatory for each item in the repository • Two levels of granularity possible • YYYY-MM-DD • YYYY-MM-DDThh:mm:ssZ • T … Z = Time zone -- must be GMT • Allows harvesting incrementally -- get only what is new since last visit • Accessed by arguments from and until

23. The question of time • What time is it? • How do you represent this moment in time in a message that goes to people in several different places around the world? • There is a standard for that. • Look up (Wikipedia will do) the ISO 8601 standard for unambiguous specification of time. • Write down what time it is right now (use minutes, but not seconds) Yes, the time will change during our discussion.

24. The OAI-PMH verbs • Each requests a specific response from a data repository

25. Identify • Function: Description of the archive • Example: http://www.language-archives.org/cgi-bin/olaca3.pl?verb=Identify • Parameters: none • Errors/exceptions: • badArgument (there should not be any) • Response format: Element Example Ordinality ‡ repositoryName My Archive 1 baseURL http://archive.org/oai 1 protocolVersion 2.0 1 earliestDatestamp 1999-01-01 1 deleteRecords no, transient, persistent 1 granularity YYYY-MM-DD, YYYY-MM-DDThh:mm:ssZ 1 adminEmail oai-admin@archive.org + compression deflate, compress * description oai-identifier, eprints, friends, … * ‡ Ordinality: 1 = mandatory, 1 only; + = mandatory, 1 only; * = optional, 0 or more

26. Actual response from http://www.language-archives.org/cgi-bin/olaca3.pl?verb=Identify <OAI-PMH xmlns="http://www.openarchives.org/OAI/2.0/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/ http://www.openarchives.org/OAI/2.0/OAI-PMH.xsd"> <responseDate>2012-03-28T21:30:33Z</responseDate> <request verb="Identify">http://www.language-archives.org/cgi-bin/olaca3.pl</request> <Identify> <repositoryName>OLAC Aggregator</repositoryName> <baseURL>http://www.language-archives.org/cgi-bin/olaca3.pl</baseURL> <protocolVersion>2.0</protocolVersion> <adminEmail>haejoong@ldc.upenn.edu</adminEmail> <earliestDatestamp>1873-04-18</earliestDatestamp> <deletedRecord>no</deletedRecord> <granularity>YYYY-MM-DD</granularity> <!-- maybe later <compression>identity</compression> --> <description>...</description> <description>...</description> </Identify> </OAI-PMH> These expand Continued

27. First expansion <description> <oai-identifier xmlns="http://www.openarchives.org/OAI/2.0/oai-identifier" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai-identifier http://www.openarchives.org/OAI/2.0/oai-identifier.xsd"> <scheme>oai</scheme> <repositoryIdentifier>OLACA.language-archives.org</repositoryIdentifier> <delimiter>:</delimiter> <sampleIdentifier>oai:ethnologue.com:aaa</sampleIdentifier> </oai-identifier> </description> Continued

28. <description> <olac-archive xmlns="http://www.language-archives.org/OLAC/1.1/olac-archive" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" type="institutional" xsi:schemaLocation="http://www.language-archives.org/OLAC/1.1/olac-archive http://www.language-archives.org/OLAC/1.1/olac-archive.xsd" currentAsOf="2012-03-28"> <archiveURL>http://www.language-archives.org/archive_records/</archiveURL> <participant name="Steven Bird" role="Curator" email="sb@csse.unimelb.edu.au"/> <participant name="Gary Simons" role="Curator" email="Gary_Simons@sil.org"/> <participant name="Haejoong Lee" role="Administrator" email="haejoong@ldc.upenn.edu"/> <institution>Open Language Archives Community</institution> <institutionURL>http://www.language-archives.org/</institutionURL> <shortLocation>Philadelphia, U.S.A.</shortLocation> <location/> <synopsis> This repository contains all records from OLAC-registered archives. It is intended to be used by services which do not want to harvest individual OLAC archives. </synopsis> <access> Metadata may be used only subject to the access permissions given by the individual archives. </access> </olac-archive> </description>

29. ListMetadataFormats • Function: retrieve available metadata formats from archive • Parameters: identifier (optional) • Errors/exceptions: • badArgument • idDoesNotExist • noMetadataFormats

30. <OAI-PMH xmlns="http://www.openarchives.org/OAI/2.0/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/ http://www.openarchives.org/OAI/2.0/OAI-PMH.xsd"> <responseDate>2012-03-28T21:38:46Z</responseDate> <request verb="ListMetadataFormats">http://www.language-archives.org/cgi-bin/olaca3.pl</request> <ListMetadataFormats> <metadataFormat> <metadataPrefix>olac</metadataPrefix> <schema>http://www.language-archives.org/OLAC/1.1/olac.xsd</schema> <metadataNamespace>http://www.language-archives.org/OLAC/1.1/</metadataNamespace> </metadataFormat> <metadataFormat> <metadataPrefix>olac_display</metadataPrefix> <schema>http://www.language-archives.org/OLAC/1.1/olac.xsd</schema> <metadataNamespace>http://www.language-archives.org/OLAC/1.1/</metadataNamespace> </metadataFormat> <metadataFormat> <metadataPrefix>olac_dla</metadataPrefix> <schema>http://www.language-archives.org/OLAC/1.1/olac.xsd</schema> <metadataNamespace>http://www.language-archives.org/OLAC/1.1/</metadataNamespace> </metadataFormat> <metadataFormat> <metadataPrefix>oai_dc</metadataPrefix> <schema>http://www.openarchives.org/OAI/2.0/oai_dc.xsd</schema> <metadataNamespace>http://www.openarchives.org/OAI/2.0/oai_dc/</metadataNamespace> </metadataFormat> </ListMetadataFormats> </OAI-PMH> Response to http://www.language-archives.org/cgi-bin/ olaca3.pl?verb=ListMetadataFormats

31. ListSets • Function: retrieve set structure of a repository • Example: archive.org/oai-script?verb=ListSets • Parameters: resumptionToken (exclusive) • Errors/exceptions: • badArgument • badResumptionToken • noSetHierarchy Sets are optional and are used to divide a repository into separate units that will be of interest to different harvesters.

32. ListIdentifiers • Function: abbrieviated form of ListRecords, retrieve only headers • Parameters: • from (optional) • until (optional) • metadataPrefix (required) • set (optional) • resumptionToken (exclusive) • Errors/exceptions: • badArgument • badResumptionToken • cannotDisseminateFormat • noRecordsMatch • noSetHierarchy

33. ListRecords • Function: harvest records from a repository • Parameters: • from (optional) • until (optional) • metadataPrefix (required) • set (optional) • resumptionToken (exclusive) • Errors/exceptions: • badArgument • badResumptionToken • cannotDisseminateFormat • noRecordsMatch • noSetHierarchy

34. GetRecord • Function: retrieve an individual metadata record from a repository • Parameters: • Identifier (required) • metadataPrefix (required) • Errors/exceptions: • badArgument • cannotDisseminateFormat • idDoesNotExist

35. Spot Check • Use the site from which we retrieved some information and use the other PMH verbs there.

38. Interoperability • The goal: communication, without human intervention, between information sources • Books that “talk to each other” • Live links for references • Knowledge of how to find relevant resources when needed • Ability to query other information locations

39. Protocols • Precise rules for interactions between independent processes • Format of the messages • Both structure and content • Specified behavior in response to specific messages • Many ways to accomplish the same result, but both sides must have the same understanding of the rules of engagement.

40. Protocol Types • RPC model • Point to point • Completely open to definition by developer • Verbs (methods) • Nouns (objects, resources) • Useful to closed community or group who know about the availability of the resource.

41. SOAP • Initial words of the acronym have been discontinued. (Simple Object Access Protocol) • Initially developed as part of the Microsoft .NET paradigm • Now in W3C committee • Stateless, one-way message exchange paradigm • XML encoded • Flexibility of RPC, but more constrained in the way communication is formatted.

42. SOAP is a lightweight protocol intended for exchanging structured information in a decentralized, distributed environment. SOAP uses XML technologies to define an extensible messaging framework, which provides a message construct that can be exchanged over a variety of underlying protocols. The framework has been designed to be independent of any particular programming model and other implementation specific semantics. http://msdn.microsoft.com/en-us/library/ms995800.aspx

43. REST • REpresentational State Transfer • An after-the-fact definition of the architecture of the World Wide Web • The model is • Client/server • Stateless • Cacheable • Layered • Resource interface constrained • Restricted verbs • Restricted content types

44. RESTful applications use HTTP requests to post data (create and/or update), read data (e.g., make queries), and delete data. Thus, REST uses HTTP for all four CRUD (Create/Read/Update/Delete) operations. • REST is a lightweight alternative to mechanisms like RPC (Remote Procedure Calls) and Web Services (SOAP, WSDL, et al.). Later, we will see how much more simple REST is. • Despite being simple, REST is fully-featured; there's basically nothing you can do in Web Services that can't be done with a RESTful architecture. http://rest.elkstein.org/

45. REST and RPC • RPC provides flexibility for any type of interaction between any type of resources • REST provides consistency to allow interaction among resources without prior discovery of accepted actions and responses.

46. SOAP and REST • Debate in the Web community about which is the better paradigm for application development • REST -- restricted, but simple extension of existing Web processes • SOAP -- added flexibility with cost in terms of bandwidth, security, complexity for development

47. References • Giving SOAP a REST http://www.devx.com/DevX/Article/8155 • SOAP Version 1.2 Part 0: Primer http://www.w3.org/TR/2003/REC-soap12-part0-20030624/#L1153 • OAI For Beginners - The Open Archives Forum online tutorial: http://www.oaforum.org/tutorial/index.php • Z39.50 Resource Page: http://www.niso.org/standards/resources/Z3950_Resources.html • Z39.50 An Overview of Development and the Future (1995) http://www.cqs.washington.edu/~camel/z/z.html Plus a few other sites as noted in the slides