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Digital Object Prototypes
An Effective Realization of Digital Object Types
K. Saidis1, G. Pyrounakis2, M. Nikolaidou2, A. Delis1
1Department of Informatics And Telecommunications2Libraries Computer Center
University of Athens
10th European Conference on Research and Advanced Technology for Digital Libraries
September 18, 2006 - Alicante, Spain 2
Outline The problem:
Develop an integrated web-based DL that manages diverse & heterogeneous digital material in a unified manner
Our proposed solution: Digital Object Prototypes – an effective
realization of Digital Object (DO) types DOPs Overview Discussion
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Pergamos: Un. of Athens DL Over 1 million objects originating
from 8 disparate collections Heterogeneous, digitised material
requiring detailed cataloguing Motivation
Simplify & speed up cataloguing Decrease development time Avoid custom coding for handling
variations of digital material
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Digital Objects Human generated artifacts
comprised of 4 components: metadata, digital content, relationships
& behaviors Several ways to encode them: METS,
FOXML, RDF, MPEG-21 Diverse kinds of material are
represented using variations of DO components
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The problem DOs (e.g. books, papers, photos etc)
should be treated in a manner that reflects the nature of the underlying “real-world” objects
DL systems do not capture, express or use the nature of DOs effectively: DL users are forced to deal with each object’s idiosyncrasies manually
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Digital Object Prototypes Introduced in last year’s ECDL A Digital Object Prototype (DOP) is a
DO Type specification, providing a detailed definition of a DO’s constituent parts: metadata, files, relationships and behaviors
With the use of DOPs, high level services can handle DO component variations in a uniform manner
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DOPs Contd. DOPs provide the means to generate
user-defined types of digital objects DO type conformance: DOs
automatically conform to their respective DOP
Inexpensive to add new types of digital material or modify existing ones (no custom coding required)
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DOPs Contd. DOPs draw on the notions of the OO
model to implement DO types All objects have a type Objects honor encapsulation Inheritance (under development)
DOs are conceived as instances of their respective prototype
Stored DOs are treated as serializations of DO instances
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A DO Instance
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Instantiation / Serialization
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DOPs 3-tier DL ArchitectureComposition of DO behaviors
DO Typing & Instantiation
Storage
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A DOP specifies Metadata element sets File types / conversions / batch
ingestions Permitted relationships Private & Public behaviors
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Behaviors Encapsulation: Private & Public
behaviors Private behaviors are executed by
the DO instance “behind the scenes” (the object itself triggers selected functionality)
Public behaviors are exposed to clients (clients trigger selected functionality)
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Metadata Specification DOPs specify:
the metadata element sets used by all objects of this type
the individual elements (fields) that constitute each set
possible mappings among elements of these sets
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Metadata Specification II Automatic loading / serialization of
metadata sets Behavioral characteristics of
metadata elements: isMandatory, isHidden, isRepeatable, defaultValue, validation
facilitate services to adjust to the object’s requirements
Mappings are automatically applied by the DO instance
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Files Specification DOPs specify:
The permitted files and their allowed formats
The information required to convert files from one format to another
Batch file ingestion / automatic DO creation process for each file
September 18, 2006 - Alicante, Spain 17
Example Historical Archive’s Senate Session
Proceedings > Folders > Sessions > Pages
What is a Page DO: A digital image stored in various
formats (e.g. high quality TIFF, web quality JPEG, thumbnail)
What is a Session DO: A complex DO, consisting of Page DOs
and session proceedings metadata
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Example Contd. Automatic file conversions
Page DOs automatically generate the two derivate formats from the high quality image
Batch Content Ingestion / DO Creation Session DOs generate Page DOs from
zip files containing high quality images
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Session DOP
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Page DOP
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Relationships DOPs specify:
The structural relationships the objects are allowed to participate in (e.g. child-of, or is-parent-of)
Whether the objects are allowed to reference other entities, either internal (residing in the same DL) or external ones
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DOPs and Collections DOPs “live” in the context of a
collection (collection pertinent scope)
Collections are represented in terms of “special-purpose” DOs
Collections may contain other collections (hierarchical namespace)
The Digital Library is the collection of all collections
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Pergamos Collections & DOPs Collection Sub collections DOPsdl theatre, papyri,
medical, folklore, histarch
-
dl.theatre - album, photo
dl.papyri papyrus
dl.medical - image
dl.folklore - notebook, chapter, page
dl.histarch senate -
dl.histarch.senate procs -
dl.histarch.senate.procs - folder, session, page
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A hierarchy of DO instances
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dl.histarch.* DOPsDOP Metadata Files Relationsfolder - Qualified DC
- EAD-like- EAD to DC mappings
none -contains session or page
session -Qualified DC-EAD-like-EAD to DC mappings
zip -contains page
page none -HQ image-Web image-Thumbnail
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dl.folklore.* DOPsDOP Metadata Files Relationsnotebook - Qualified DC none -contains chapter
or page
chapter -Qualified DC zip -contains page
page none -HQ image-Web image-Thumbnail
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dl.papyri.* DOPsDOP Metadata Files Relationspapyrus Qualified DC -Original Image
-Processed image-Web image-Thumbnail
none
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dl.theatre.* DOPsDOP Metadata Files Relationsalbum -Custom
(theatrical play metadata)-DC-Custom to DC mappings
none contains photo
photo Qualified DC -Original Image-Web image-Thumbnail
none
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Summary We argue that digital objects do have
types (they fall into categories with uniform characteristics and behavior)
First realization of DO Type conformance: DOs honor the specifications residing in their DOP automatically
Effective management of diverse digital material: the DL system interprets DO types, not the user
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Future Work Implementation of DOPs inheritance
(reuse: new types can be derived from existing ones)
Offline DOP validation process Make DOPs operate independently
of the underlying repository Open source release of the DOPs
framework
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Thank you Questions?
Email: saiko@di.uoa.gr DOPs in action: Pergamos demo
tomorrow (Poster #17)