Digital Objects, Data Models, and Surrogates. Carl Lagoze Computing and Information Science Cornell University

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1 Digital Objects, Data Models, and Surrogates m Computing and Information Science Cornell University

2 Pathways Project NSF grant number IIS PIs:, Sandy Payette, Herbert Van de Sompel, Simeon Warner Research Participants: Lyudmila Balakireva, Jeroen Bekaert, Xiaoming Liu, Chris Wilper, Zhiwu Xie

3 Lots of types of digital objects Lot s of data models.

4 Dienst

5 Fedora

6 OAI-PMH Resource Abstract content Item Available structured data about the resource Record Disseminated structured data about the resource

7 MPEG-21 DID

8 METS

9 Interoperability Layer m Obtain DSpace arxiv Fedora adore eprints Harvest Put Shared Data Model Shared Serialization of Model Shared Services on Model Individual Models and Interfaces

10 First pass: Graphite Model Graph-based abstraction as common reduction across heterogeneous models (Payette and Erickson) Basis for linking distributed identified resources (content, data, services)

11 Pathways Core: Graph-based Data Model (Bekaert, Lagoze, Liu, Payette, Van de Sompel, Warner) Abstract Concrete

12 Basis for a Network of Linked Objects

13 Why not just asset transfer? Full transfer is only necessary for some applications e.g., preservation mirroring In fact, it some cases it is forbidden and/or undesirable So, the infrastructure and model should accommodate but not be limited to transfer

14 By not committing to asset transfer Avoid embedding IP issues into the core interoperability layer Accommodate service-tuned asset transfer Allow live references, rather than static copies

15 m Model Core Requirement Identity independent of specific schemes Lineage relationships among objects evidence of workflow for evidential citation Semantics associated with entities facilitate service mapping Recursion for n-levels of entity containment Link to concrete representation Assertion of persistence levels

16 Data Model

17 m Identity

18 m Lineage Relationships

19 m Semantics

20 m Recursion

21 m Concrete Representation

22 m Persistence Guarantees

23 Serializing the Data Model Surrogate is a serialized and transportable representation of a digital object according to the model Accessed via obtain and harvest Deposited via put Prototype serializes via RDF/XML Serializations in other formats possible e.g., DIDL, METS

24 Surrogates <-> Identity providerinfo records obtain information {provider, id, version} in surrogate makes it an evidential record of the digital object, provided by a specific service, in specific version

25 Surrogate <-> Persistence hasproviderpersistence expresses commitment of provider to persistence of entity handle Commitment can vary: e.g., transient, handle persists, versions persist, object is stable

26 RDF/XML Representation of the Model

27 RDF Graph Surrogate

28 REPO :10 REPO :11 REPO :11 DOI:1 preferredid provider DOI:1 preferredid provider DOI:1 preferredid provider hasproviderinfo hasproviderinfo hasproviderinfo DOI:1 original Source haslineage DOI:1 in French haslineage DOI:1 in German hasdatastream hasdatastream hasdatastream re que st requ est obtain access reply reply arxiv mediate Fedora obtain access request ingest put DSpace English- > French xlate French- >German xlate