1. The document discusses modeling the content of digital libraries and information systems. It proposes modeling all entities as resources related through relationships. This allows modeling of complex information objects, composites, versions, and annotations. 2. Key constructs proposed in the model include modeling all entities as resources related through relationships. This includes information objects, actors, functions, as well as concepts and ideas. The model also distinguishes between works, manifestations, and items through relationships. 3. Metadata is defined as any data used to discover, interpret, or use information objects. Metadata resides in the relationships between resources rather than in the resources themselves. This allows flexible modeling of provenance, context, and other usage data.

1. 1
Digital Library Content Model
Dagobert Soergel
College of Information Studies
University of Maryland
Department of Library and Information Studies
University at Buffalo

2. 2
The Problem
Digital libraries must
1. Store a wide variety of often complex information objects
and display these objects on different platforms.
This requires modeling information objects, their internal
structure, and relationships among them.
2. Provide data that support discovery, interpretation, use,
and management of information objects.
This requires a good metadata model
3. Support annotation of information objects.
Annotations turn out to be surprisingly diverse.
An annotation my refer to only a part of an information object.
This requires an elegant model that can deal with many cases.

3. 3
Purpose of the talk
To reexamine a number of basic notions regarding
the content of a digital library (or, more generally, any
information system) to achieve sound definitions
Developed in the framework of the
DELOS Digital Library Reference Model
a framework for describing digital libraries, their content,
users, and functions and, for each, their qualities and
associated policies

4. 4
Premisses
• Modeling the content domain is complex and much
thinking is muddled
• Need to be able to handle both “data” and “documents”
• Any reference model
• needs to be abstract and must not commit to any
particular standard or design decision
• rather, it must provide a framework for specifying
the commitments of any particular DL
(or information system)

5. 5
Issues
0 Scope of this talk and modeling constructs
1a Content in the overall context of a DL reference model
1b Modeling information objects
1c Levels, versions, and relationships
1d Composite information objects / resources
1e Resource identifiers
2 Metadata, including provenance, context, usage
3 Annotation

6. 6
Scope of this talk
• A reference model for a broadly conceived digital
library will be able to model most any information
system, thus will be useful very broadly.
• The focus on digital libraries is in the application,
especially the type of collection, to which the model is
applied.

7. 7
Scope: level of abstraction
• The reference model should stay on an abstract level. It should
not require specific standards but rather
allow for plugging in any standard, such as RDA or DC.
• A DL should indicate to the users what standard it uses
for things like time, place, type of relationship, type of resource
• The reference model should
not require design choices but rather
provide a framework for specifying design choices,
such as selectivity of the collection. A DL will then indicate
whether its collection is selective or fully inclusive

8. 8
Modeling constructs
• The reference model should be based on an
entity-relationship model (E-R model).
• Second-order logic: relationship instances are resources that
can in turn be related to anything.
Apply pragmatically for useful navigation and common-sense
inferences; stay away from types of reasoning that run into
problems with second order logic.
• Must add mechanisms for indicating the degree of precision or
the degree of certainty of statements.

9. 9
Issues
1a Content in the overall context of
a DL reference model
1b Modeling information objects
1c Levels, versions, and relationships
1d Composite information objects / resources
1e Resource identifiers
2 Metadata, including provenance, context, usage
3 Annotation

10. 10
Content in the overall context of a
DL reference model
• Resources
• Structured data
• Unstructured data, text
• Uses of data

11. 11
Everything is a resource
W3C definition
A resource is anything that can be identified or named.
Any resource is represented by a resource identifiern
Resource includes
● external (non-digital) objects or events and
● digital object or event,
wherever that digital object or event may reside or occur.
Same as topic in topic maps
In an E-R model, entity types, entity instances (entity values),
relationship types, and relationship instances are all resources
In RDA: Resource restricted to information object.
Advantages of broader definition will become clear.

12. 12
Structured data = statements
Resource 1 <relationship> Resource 2
SoftwareModule <createdBy> LegalEntity
SoftwareModule <annotatedBy> Information object
Event <happenedIn> (Date1, Date2)
Multi-way relationships, frames
Statements are information objects, that is, they are
resources that can in turn be related to anything
Statement also called proposition or assertions (or fact)

13. 13
More on structured data
Data consist of statements about resources.
Such statements can be conceived as relationship instances
in which the resource in focus occupies one argument slot.
A simple statement using a binary relationship or a
multi-way relationship (a frame instance with slots filled)
(objects in an object-oriented database)
Drug treatment frame instance
Drug Taxoteer
treatsDisease Cancer, estrogen-negative
inPopulationGroup Elderly
hasSuccessRate 55%

14. 14
More on structured data
Slot fillers are also known as data values.
A data value makes sense only when it is seen in relation to
one or more resources, for example as a slot filler in a frame.
Examples
The value 55% makes sense only in the right context, such as in
the success slot of a drug treatment frame
The value 185 cm makes sense only if we know it is the height of
a person or the length of a pair of skis.

15. 15
There are two ways to communicate such statements.
1. Structured data:
One learns what one wants to know about the resource in
focus immediately from a relationship instance.
Hamlet <authoredBy> Shakespeare
The drug treatment frame on Taxoteer
The actual data of interest are represented in a database

16. 16
There are two ways to communicate such statements.
2. Unstructured data:
One needs to extract what one wants to know from a text or
image that is related to the resource in focus.
Shakespeare schrieb den Hamlet im Jahre 1625
Hamlet wurde von Shakespeare verfasst
Taxoteer ist effektiv in der Behandlung von Krebsen die keine
Rezeptoren fuer Estrogen haben. In aelteren Personen liegt
die Erfolgsrate bei 50%.
The data of interest are stored in what is commonly known as
document.

17. 17
Functions of data
Data about a resource may serve any of the following functions:
• learn about the resource and its various characteristics
• learn about the history and context of the resource
• learn how to use the resource
• manage the resource
• preserve the resource
The sections about metadata (roughly: data about an information object)
will specialize this list

18. 18
Relationship as the
basic modeling construct
Important principle:
Many concepts in a DL reference model are best modeled
based on relationships rather than based on entities
For example, “annotation-hood”
resides not in an information object but in the relationship
InformationObjectA <annotates> InformatioObjectB
InformationObject B <annotatedBy> InformationObjectA

19. 19
Resource type examples
• Information objects
Incl. documents, data streams, databases, queries and their
results (virtual information objects, such as database reports,
virtual collections)
• Actors that can search for, create, and manage resources
• Functions and services
• Software modules
• Policies
• Languages
• Ideas, concepts

20. 20
Inheritance
Many reference model constructs are specified at the level of resource.
They inherit down to the different resource types, especially
information objects
For example, the following statement types are valid for Resource
Resource <identifiedBy> Identifier
Resource <characterizedBy> QualityParameter
Resource <regulatetBy> Policy
Therefore, they are also valid for InformationObject or Actor or Policy

21. 21
Issues
1a Content in the overall context of a DL reference model
1b Modeling information objects
1c Levels, versions, and relationships
1d Composite information objects / resources
1e Resource identifiers
2 Metadata, including provenance, context, usage
3 Annotation

22. 22
Information objects 1
1. A formal relationship instance
(such a row in a table or a structured data record)
2. A document (written or spoken text, image, sound) from which a
human reader can learn about the resource in focus or about the
relationships among several resources.
Information extraction: document → formal relationship instances.
A collection of information objects is in turn an information object
• a table in a relational database = a collection of rows, each
representing a relationship instance or a collection of relationship
instances
• a collection of documents

23. 23
Information objects 2
An information object may be a close representation of an
external object or event, for example
• An image (photograph or painting) of a building. There may be
many such images taken from different angles etc.
• A video recording of a soccer game. There may be several
such video recordings, each capturing different scenes, or
capturing the same scene from different angles, or following
different players, etc. These are different information objects
representing the same external event.

24. 24
Real world objects, concepts, ideas
To provide full access to the information objects it contains,
a digital library must manage data about any kind of object
(real world objects, concepts, ideas) in its subject domain.
Why?
1. The DL may represent data in the form of a database
2. Users look for information objects that deal with or are
digital representations of any kind of object.
This idea underlies Topic Maps which were originally designed to
improve access to documents by relating the topics discussed in
these documents.

25. 25
Real world objects, concepts, ideas
Examples (these are all resources)
• People (focus of biographical reference tools)
• Organizations (focus of organization directories)
• Events (focus of developing "event gazetteers")
• Places (focus of gazetteers)
• Dates
• Mathematical theorems (focus of mathematical encyclopedias)
• Concepts, ideas
• Problems and proposed solutions
• Computer programs (focus of software directories or libraries)
The reference model should have a more complete list and indicate
sources dealing with these

26. 26
Issues
1a Content in the overall context of a DL reference model
1b Modeling information objects
1c Levels, versions, and
relationships
1d Composite information objects / resources
1e Resource identifiers
2 Metadata, including provenance, context, usage
3 Annotation

27. 27
Levels, versions,
and relationships
• Work, manifestation, item (individual copy)
• Linked through relationships

28. 28
Work
Intellectual or artistic entity, as the abstract essence or as a text,
image, or piece of music.
Range:
• A basic story or theme
• the story of Faust
• the myth of the Great Flood
• A text telling the story, such as
• Goethe's Faust
• the account of the Great Flood in the Bible (original Hebrew)
• the account of the same myth in another culture
• A specific version of the account in the Hebrew Bible
a Latin translation of the account in the Hebrew Bible

29. 29
Manifestation
A specific rendering of a work by means of a graphical image or
sound, taken in the abstract; the idea of such a rendering.
Examples:
• The text of Goethe's Faust printed in a particular typeface and layout
A performance at which the text is recited also renders the text but is
more properly considered a separate, but related, work.
• A specific score of a given version of Schubert's Fifth.
A performance of that version of Schubert’s Fifth also renders the
piece of music but is considered a separate, but related, work.
Also the rendering of a work in the form of digital storage that can be
transformed to a graphical image or sound, again taken as the abstract
pattern of digital signals.

30. 30
Item, individual copy
The embodiment of a manifestation in a physical object
We can perceive the content of an manifestation only through an
individual copy of it (unless we have memorized the visual expression
manifest in a manifestation and can conjure it up from memory).
There are works that have only one manifestation of which there is
only one copy.

31. 31
Relationships among information objects
The story of Faust <dealsWith> Pact with the devil
The story of Faust <isToldIn> Marlow’s Faust
The story of Faust <isToldIn> Goethe’s Faust
Goethe’s Faust <authoredBy> Goethe, Johann Wolfgang von
Goethe’s Faust <hasManifestation> R1231
R1231 <publishedBy> Cotta
R1231 <hasDate> 1871
R1232 <isCopyOf> R1231
R1232 <ownedBy> (HRieth, 1896, 1956)
R1232 <ownedBy> (DSoergel, 1956, *)

32. 32
Hierarchical inheritance
• Data about a work inherit to all works below it along <isToldIn>,
<hasVersion> etc. Therefore
Goethe' Faust <dealsWith> Pact with the devil
• Data about a work inherit to all its manifestations. Therefore
R1231 <authoredBy> Goethe, Johann Wolfgang von
• Data about a manifestation inherit to all its items
• Hierarchical inheritance increases efficiency
• More efficient catalog input
• More efficient catalog storage
• More efficient representation and reading of search results

33. More relationships
R271 The man I killed, by Michael Halliday
R519 The man I killed, play by Christopher Wern
R519 <isBasedOn> R271
R315 Handbook of commercial geography, by Robert
Chisholm
R783 Chisholm's handbook of commercial geography,
entirely rewritten by L. Dudley Stamp and S.
Carter Gilmour.
R783 <entirelyRewrittenFrom> R315
33

34. 34
Relationship to FRBR
Notes on Terminology
• The FRBR distinction between work and expression should
be rethought. It is unclear and consequently poorly
understood, and it may not be necessary. Just have work.
The intuition FRBR tries to capture in this distinction is better
handled through relationships among works as defined here.
• Following FRBR I use the term manifestation.
Other term: edition (in the sense of German Ausgabe),
but edition also means German Auflage,
so use of the term edition can be confusing.
• It would be nice to be able to use graphic expression as a
synonym for rendering, but to avoid any further confusion with
FRBR it is best not to use the term expression at all.

35. 35
Version control
Important, but not elaborated here

36. 36
Issues
1a Content in the overall context of a DL reference model
1b Modeling information objects
1c Levels, versions, and relationships
1d Composite information objects /
resources
1e Resource identifiers
2 Metadata, including provenance, context, usage
3 Annotation

37. 37
Composite information objects / resources
Examples
• Book divided into chapters, sections, paragraphs, words (XML
Document Object Model, DOM or TEI)
Each part can be seen as a separate information object
• Movie with images, soundtrack, close captions, script, all
coordinated (MPEG-7)
• A medical record with patient data, test data, images, live
monitoring data streams, diagnoses, drugs prescribed, etc.

38. 38
Composite information objects / resources
Abstractly:
Each component is a separate information object,
composition expressed through relationships
In practice:
Many document models for composite (or compound)
documents supporting presentation
DL needs to allow specification, for each document,
of the particular document model used

39. 39
Issues
1a Content in the overall context of a DL reference model
1b Modeling information objects
1c Levels, versions, and relationships
1d Composite information objects / resources
1e Resource identifiers
2 Metadata, including provenance, context, usage
3 Annotation

40. 40
Identifying information objects
1 Initial definition upon entry into the digital library.
2 Definition on the spot
Examples
Annotate a specific segment of a text document or a region
of an image or sound document or
Anchor an annotation to a specific location in a document.
The segment or anchor is a new information object that is
included in the original information object, and this new
information object is linked with any of several annotation
relationships to a new information object created by the user.
Related to composite objects. More on this under annotation

41. 41
Issues
1a Content in the overall context of a DL reference model
1b Modeling information objects
1c Levels, versions, and relationships
1d Composite information objects / resources
1e Resource identifiers
2 Metadata, including provenance,
context, usage
3 Annotation

42. 42
Data about information objects
Metadata =
data about information objects
if used for discovering, interpreting, and using information objects
Relate information objects to other types of resources. Examples:
InformationObject <hasCreator> Actor
InformationObject <dealsWith> Actor
InformationObject <containsText> Text (or, more specifically Word)
Relate a word in a text to the concept that is the meaning in which the
word is used in this particular position.
InformationObjectA <hasAbstract> InformationObjectB
InformationObjectA <hasCriticalCommentary> InformationObjectC
InformationObjectD <hasSupportiveCommentary>InformationObjectC

43. 43
More on defining metadata
The “metadata-hood” of an information object does not reside in the
information object, but in its relationship to another information
object and, more specifically, in its use
A piece of data
is used as metadata
if it is used for the purpose of discovering, interpreting, and
using information objects, which then give the ultimate data
wanted.
The same piece of data may fill the ultimate need to of the user in
one situation and be used as metadata in another situation.

44. 44
Not metadata
• Data about resources that are not information objects are not
metadata even if they are similar in form.
• Data about information objects are not always used as metadata.
For example, using author data to count a faculty members
publications or citation data to compute impact
• Extensive discussion of what exactly is the definition of metadata is
not a good use of resources. A system should provide the data that
are useful to a user for whatever purpose; what each piece of data is
called is less important.

45. 45
Metadata typologies
Metadata (and data in general) can be divided into categories from
several perspectives, and within each perspective there exist
several approaches.
Some examples of how to categorize metadata
• by purposes or use. Since the same unit of metadata can be
used for several purposes, the resulting categories overlap.
• by source, for example, extracted, assigned by cataloger,
assigned by user (social tagging), from usage tracking
• by intrinsic characteristics, for example data about
provenance or about the format of the information object

46. 46
Some metadata uses
A Learn about information objects and interpret them; this includes
A1 Learn about the identity and characteristics of information objects
(descriptive metadata)
A2 Learn about the history and other features of the context of the
information object (contextual metadata)
B Learn how to use an information object, including
B1 Learn how to gain legal access (access and rights metadata)
B2 Learn how to gain technical access to the information object
(what machinery and software is needed to access the
information object for a given purpose, such as assimilation by a
person or processing by a computer program)
C Manage information objects (administrative metadata), in particular
C1 Manage the preservation of information objects
(preservation metadata).

47. 47
Usage data
Data on usage of resources
and on usage rights, usage history, future use / preservation important
for discovering, interpreting, and using resources as well as managing
resources
Some of these data can be collected automatically
If the resource in question is an information object, this kind of data is
often used as metadata

48. 48
Issues
1a Content in the overall context of a DL reference model
1b Modeling information objects
1c Levels, versions, and relationships
1d Composite information objects / resources
1e Resource identifiers
2 Metadata, including provenance, context, usage
3 Annotation

49. 49
Annotation
InformationObjectA <annotatedBy> InformationObjectB
InformationObjectB may be created on the spot in order to annotate A
(InformationObjectB and the annotation relationship have the same
author) or B may preexist (the annotation relationship between A and B
is introduced by a third party)
Specific type of annotation expressed by specializing the annotatedBy
relationship, for example
InformationObjectA <criticizedBy> InformationObjectB
InformationObjectA <hasCriticalCommentary> InformationObjectC
InformationObjectD <hasSupportiveCommentary> InformationObjectC
InformationObjectE <isPartOfSpeech> PartOfSpeech
Annotation-hood is in the relationship, not in the information object

50. 50
Annotation
Annotation-hood is in the relationship, not in the information object
There is a wide range of relationship types that are called annotations.
Linguists think of annotations differently than scholars making
comments on a text.
Rather than trying to define exactly what “annotation” means, the
reference model should include a comprehensive list of relationship
types that might be considered annotation by somebody so that
anybody can define their meaning of annotation by giving the
appropriate subset of annotation relationship types.
The same thought applies to metadata, discussed on a later slide.

51. 51
Special resource types for annotations
Some annotations require special types of resources.
Examples
Annotate a text with part-of-speech indications
annotated resource : a one-word fragment of the text
annotating resource: a value from a list of parts of speech
Annotate a text with meaning for word sense disambiguation
annotated resource : a word or phrase in the text
annotating resource: a value from a list of meanings defined in some way
Annotation through underlining or other marks
annotated resource : a fragment of text or other information object
annotating resource: a pair (sign, meaning), e.g. (underline, important) or
(?, check this out) or (X, nonsense)
The annotated resource and the annotating resource may be very short

52. 52
Annotation and metadata
Metadata and annotation data overlap, and different
communities and individuals have different definitions of what is
included in metadata and what is included in annotations.
The precise nature of a unit of data about an information
object is determined by the relationship type and the resource
that is linked to. The interpretation of each type of data is in the
eye of the beholder.
Need an inventory of relationship types (a type of ontology)
For example, the CIDOC Content Reference Model (CIDOC/CRM)
is an inventory of broad relationship types.
In such an inventory, one could indicate who considers a given
relationship type as usable as metadata and/or as belonging to
annotation.

53. 53
Take-home message 1
The entity-relationship model (E-R model) provides
the unifying principle for a digital library content model
The E-R model allows representation of structured data of
any complexity on a conceptual level.
Defining relationships between information objects handles
• Modeling information objects
• Levels, versions, and relationships
• Composite information objects / resources
• Metadata
• Annotation
Many notions are captured better through
relationships than fine distinctions of entity types

54. 54
Take-home message 2
Any reference model
• needs to be abstract and must not commit to any
particular standard or design decision
• rather, it must provide a framework for specifying
the commitments of any particular DL
(or information system)
A reference model provides
a systematic framework for description and analysis,
not a prescription

55. Dagobert Soergel
dsoergel at umd.edu
www.dsoergel.com
55

56. Omitted slides
56

57. 57
Construction process
• Need to be sure all applicable concepts from various
sources such as the 5S model and FRBR/CRM are
included, either in the skeleton model or in a list of
values / choices, as appropriate
• There is still work to be done to pull reference model
subject matter out of the reference architecture
document, and vice versa.

58. 58
Construction process
• We should have an online version of the reference
model document with the following properties
• Links to discussion of issues and underlying
rationale, capturing some of the discussion in the
group.
• Links from the reference model to the appropriate
section of the reference architecture
• The Wiki page may not quite do it.

59. 59
There are two ways to communicate such statements.
1. One learns what one wants to know about the resource in
focus immediately from a relationship instance.
Hamlet <authoredBy> Shakespeare
The drug treatment frame on Taxoteer
The actual data of interest are represented in a database that
captures these statements (relationship instances), such as
a collection of Prolog statements
a relational database
an object-oriented database
2. One needs to consult an information object that is related to
the resource in focus.
Shakespeare schrieb den Hamlet im Jahre 1625
Hamlet wurde von Shakespeare verfasst
Taxoteer ist effektiv in der Behandlung von Krebsen die keine
Rezeptoren fuer Estrogen haben. In aelteren Personen liegt die
Erfolgsrate bei 50%

60. • The DL designer must decide how to identify
the new resource that is a part of an existing
resource and
the new text object created by the annotator
and how to store the link between these two
information objects
60

61. 61
Identifying information objects
Architecture issues
Definition on the spot, options
(1) use completely independent identifiers and store the relationship explicitly
(2) use dependent identifiers
The part of a document can be identified by
document identifier followed by information that uniquely identifies the part.
The part relation is implied by the structure of the identifier.
The annotation information object could be identified by
the identifier of the resource being annotated followed by a short string that identifies the nth
annotation of this resource (like a footnote).
The relationship between the resource and the resource annotating it would be implied by
the identifier (however, the specific type of the annotation relationship would not be captured
this way).
The resource that annotates still can be referenced from any other context.
Implicit representation
Embedded annotations: The annotation is embedded in the document, linked to a point in a
text that is identified only by the place of the annotation. This could be converted to an
explicit representation.

62. 62
Some metadata uses
This is a specialization of the functions of data given above
A learn about other data, that is, information objects, and understand them; this includes
A1 learn about the identity and characteristics of information objects
(descriptive metadata)
A2 learn about the history and other features of the context of the
information object (contextual metadata)
B learn how to use an information object (source of data), including
B1 learn how to gain legal access to the information object
(access and use rights metadata)
B2 learn how to gain technical access to the information object
(what machinery and software is needed to access the information object
for a given purpose, such as assimilation by a person or processing by a
computer program)
C manage information objects (administrative metadata), in particular
C1 manage the preservation of information objects (preservation metadata).

63. 63
Metadata in the reference model
When describing a DL using the reference model,
need to be able to indicate any typology of metadata
used in the DL