Dewey linked data:
making connections with old friends
and new acquaintances
Joan S. Mitchell, Michael Panzer
We adress the history, uses cases, and future plans associated with
the availability of the Dewey Decimal Classification (DDC) system
as linked data. Parts of the DDC have been available as linked
data since 2009. Our initial offering included the DDC Summaries
(the top three levels of the DDC) in eleven languages exposed as
linked data in dewey.info, an experimental web service. In 2010, we
extended the content of dewey.info1 by adding assignable numbers
and captions from the Abridged Edition 14 data files in English,
Italian, and Vietnamese. In mid-2012, we -extended the content
of dewey.info yet once again by adding assignable numbers and
captions from the schedules and geographic table in the latest full
edition database, DDC 23. We will discuss the behind-the-scenes
development and data transformation efforts that have supported
these offerings, and then turn our attention to some uses of Dewey
linked data plus future plans for Dewey linked data services.
1http//dewey.info.
JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013).
DOI: 10.4403/jlis.it-5467
http//dewey.info
http://dx.doi.org/10.4403/jlis.it-5467
J.S. Mitchell, Dewey linked data
History
The history of Dewey linked data is an evolving story of opportunity
and experimentation, with an eye toward usability and use of the
data. In 2009, the DDC 22 Summaries, an authorized derivative
work based on the top three levels of DDC 22, had already been
translated into ten languages (more languages than the full edition
of the DDC on which the data were based). We decided to experi-
ment with making the DDC Summaries available as linked data in
an experimental web service, dewey.info. Our initial design goals
included:
• provide an actionable URI for every class;
• encode the classification semantics in RDF/SKOS;
• provide representations for machines and for humans;
• make the data usable under a widely understood license used
in the Semantic Web community.
Publishing Dewey as linked data required development decisions
on several different fronts. First of all, we had to develop a URI pat-
tern that would support the identification of several different kinds
of entities and relationships. The URIs had to act as dereferenceable
identifiers that could deliver representations of the referenced re-
sources in a RESTful manner. Each class had to be identified with a
URI and the data had to be presented in a reusable way. In develop-
ing the URI pattern, we had to provide for the full complexity of the
DDC at any time: identification of the scheme, parts of the scheme,
edition, language, and time slice. Figure 1 shows the status of DDC
22 at the time of initial development of URIs for the DDC.
DDC 22 was initially published in 2003; the various DDC 22 transla-
tions were published in 2005 (German), 2007 (French), 2009 (Italian),
JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013). Art. #5467 p. 178
JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013)
Figure 1: Versions of the DDC based on DDC 22.
JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013). Art. #5467 p. 179
J.S. Mitchell, Dewey linked data
and 2011 (Swedish-English mixed version). Abridged Edition 14 (a
logical abridgment of DDC 22) was published in 2004; translations
followed in 2005 (French), 2006 (Italian and Vietnamese), and 2008
(Hebrew and Spanish). The DDC Summaries based on DDC 22
were published in English and ten other languages at the time of the
introduction of dewey.info. Besides the DDC Summaries, figure 1
includes two other authorized derivative works based on DDC 22:
200 Religion Class (2004), an updated subset of DDC 22; Guide de
la classification décimale de Dewey, a French-language customized
abridgment of DDC 22, and DDC Sachgruppen, a German transla-
tion of selected DDC 22 top-level classes (including some below the
three-digit level) developed for the primary use case of organizing
the national bibliographies of Germany, Austria, and Switzerland
(the four languages in the box on the right-hand side of figure 1 are
translations of DDC Sachgruppen; all five language versions are
used in the national bibliography of Switzerland).
Dewey.info includes representations for machines and humans; the
latter is particularly important in order to illustrate the DDC data
offerings to a wider community beyond traditional users of value
vocabularies from the library community. The data in dewey.info
are presented in human (XHTML+RDFa) and machine (RDF) ver-
sions (the machine version of dewey.info has three different RDF
serializations: RDF/XML, Turtle, and JSON). The Dewey URIs have
the following general pattern: http://dewey.info/{object-collection}/
{object}/{snapshot-collection}/{snapshot}/about}. Specific documents
have a variable resource name component and allow specification
of content language and type (format):
http://dewey.info/{object-collection}/{object}/{snapshot-collection}/
{snapshot}/{resource-name}.{language}.{content-type}.
An object is a member of the DDC domain and part of an object
collection. The object collection specifies the type of the object. The
object collection is a mandatory component and can have one of the
values ”scheme,” ”table,” ”class,” ”manual,” ”index,” ”summary,”
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and ”id.” A specific object from that collection follows if required.
For example:
http://dewey.info/class/576.83/
http://dewey.info/scheme/
http://dewey.info/table/2/
A snapshot is used to refer to versions of objects at specific points
in time. Snapshots can be part of a snapshot collection, e.g., ”e22,”
referring to every concept version that is part of Edition 22 of the
DDC. In the following examples, the first URI is an example of a
snapshot, the second is an example of a snapshot collection, and the
third is an example of a snapshot-collection/snapshot/ combination.
snapshot-collection/snapshot/.
http://dewey.info/class/641/2009/
http://dewey.info/class/641/e22/
http://dewey.info/class/641/e23/2012-08/
Language and format are also accommodated in the URI:
http://dewey.info/class/641/about.it
http://dewey.info/class/641/about.rdf
http://dewey.info/class/641/about.it.html
While SKOS is often the RDF vocabulary of choice for represent-
ing controlled vocabularies on the Web, its initial development was
largely informed based on thesaurus-like knowledge structures.
Panzer (“DDC, SKOS, and linked data on the web”) and Panzer and
Zeng (“Modeling Classification Systems in SKOS: Some Challenges
and Best-practice Recommendations”) have noted some of the chal-
lenges in representing classification data in SKOS. Since the initial
DDC linked data offering did not include complicated note types
and relationships between classes other than those expressed by the
notational hierarchy, the shortcomings in SKOS noted elsewhere
with respect to the representation of classification data did not pose
JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013). Art. #5467 p. 181
J.S. Mitchell, Dewey linked data
a major roadblock in the exposure of the DDC 22 Summaries in
dewey.info.
The query http://dewey.info/class/641/about.it.rdf delivers the
following machine-actionable representation in RDF/SKOS, which
focuses on presenting concept metadata together with number and
caption information plus basic semantic relationships.
Note that the two main entities retrieved are http://dewey.info/
\class/641/ and http://dewey.info/class/641/2007/02/about.it,
connected through a dct:hasVersion relationship:
Listing 1: Example of concept metadata representation in RDF/SKOS.
OCLC Online ComputerLibrary Center, Inc.
it
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http://dewey.info/class/641/about.it.rdf
http://dewey.info/\class/641/
http://dewey.info/\class/641/
http://dewey.info/class/641/2007/02/about.it
JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013)
641
Cibi e bevande
2000-01-01T00:00:00.0+01:00
2006-01-28T22:04:16.000+0100
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J.S. Mitchell, Dewey linked data
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JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013)
641
skos:notation>
641
Finally we needed an appropriate license model. We make data
on dewey.info available under a Creative Commons BY-NC-ND
license.2Licensing information is embedded in RDF and RDFa fol-
lowing the Creative Commons Rights Expression Language (ccREL)
specification.3 In the RDF/SKOS extract above, the following licens-
ing information is embedded in the RDF:
Listing 2: CC license embedded in RDF/SKOS
OCLC Online Computer Library Center, Inc.
2http://creativecommons.org/licenses/by-nc-nd/3.0.
3http://wiki.creativecommons.org/CcREL.
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http://creativecommons.org/licenses/by-nc-nd/3.0
http://wiki.creativecommons.org/CcREL
J.S. Mitchell, Dewey linked data
A year after the initial offering, we extended the data available in
dewey.info with the addition of assignable numbers and captions
from Abridged Edition 14 in three languages (English, Italian, and
Vietnamese). This extension added about 3500 additional records for
each language to the data already available in dewey.info. While the
DDC Summaries represented a broader set of languages than avail-
able in the full and abridged translations, the new abridged-edition
offerings were a subset of the languages in which the edition had
been translated. Why were English, Italian, and Vietnamese chosen?
The simple answer was that each was available in the same propri-
etary format, ESS XML, for which we already had an RDF/SKOS
transformation.
Parallel to the linked data work, the Dewey editorial team was
making a major data transformation of another type—moving from
the proprietary ”ESS” format to one based on the MARC 21 Clas-
sification and Authority formats. In 2009, the DDC Summaries
were transformed from ESS XML to RDF/SKOS; we used the same
transformation to make the Abridged Edition 14 data available in
dewey.info. In 2010, OCLC moved to a new underlying represen-
tation for the DDC, adopting one based on the MARC 21 formats
for classification data (to represent class records) and authority data
(to represent Relative Index and mapped terminologies associated
with class records). At the same time, OCLC adopted MARCXML
as the distribution and ingest format for DDC data across versions,
and moved to a new data distribution and ingest model (previously,
data transfers were handled at the individual file level over an ftp
site). We made a decision to delay the distribution of additional
DDC data in dewey.info until we could productionize the data trans-
formation and distribution process operating on the new format
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JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013)
and within the distribution environment. This meant taking the
data encoded in MARCXML from the distribution server, applying
the RDF/SKOS transformation stylesheet, and associating the result
with a ”subscription,” automatically creating an Atom feed of data
sets that a user agent (in this case, dewey.info) could pick up from
the distribution server over a RESTful interface. A model of the
process is shown in figure 2.
Figure 2: Dewey distribution environment.
We installed the pieces on the distribution server that would make
this possible in May 2012. In in mid-June 2012, we added assignable
numbers and captions from the DDC 23 schedules will be available
to dewey.info ; this addition of over 38,000 numbers increased the
available Dewey linked data nearly tenfold. In August 2012, we fur-
ther extended Dewey linked data by adding the assignable notation
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J.S. Mitchell, Dewey linked data
and captions from Table 2 (the Dewey geographic table).
Next steps
Our next planned offering is the linking of ”new acquaintance,”
GeoNames, to Table 2 data. Because we want to manage all editori-
ally curated data (including mappings) with the OCLC ESS system,
this will require short-term and long-term changes to geographic
data within the system. In order to allow the provision of geographic
data on the class level, the Dewey editorial team developed MARC
PROPOSAL NO. 2011-10,4 which was approved by MARBI in June
2011. The proposal defines new fields that allow for the storage
and display of geographic codes in MARC classification records,
thereby enabling the reuse of parts of the Relative Index links to
GeoNames (generated by the matching algorithm) on the class level
in applications downstream, e.g., in linked data representations of
the DDC.
Use cases
In addition to linking plans, we report on use cases that facilitate
machine-assisted categorization and support discovery in the Se-
mantic Web environment. It is important to have use cases for
Dewey linked data, and to solicit new use cases that might inform
decisions about our data offering. Institutions such as Bibliothèque
nationale de France, the British Library, and Deutsche Nationalbib-
liothek have made use of Dewey linked data in bibliographic records
and authority files .FAO has linked AGROVOC to our data at a gen-
eral level. We are also exploring links between the DDC and other
4http://www.loc.gov/marc/marbi/2011/2011-10.html.
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http://www.loc.gov/marc/marbi/2011/2011-10.html
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value vocabularies such as VIAF, FAST, ISO 639-3 language codes,
and MSC (Mathematics Subject Classification). Today, we would
like to focus on three uses cases, a caption service, the ”old friend” of
DDC synthesized number components associated with categorized
content, and the ”new acquaintance” of DDC-GeoNames links.
Caption service
Querying Dewey linked data
The first use case is a simple one: querying Dewey linked data by a
Dewey number to have the associated caption delivered as an expla-
nation of the number. For example, the query http//dewey.info/
class/945.5/about will return information about class 945.5, includ-
ing the captions ”Regione della Toscana” and ”Tuscany (Toscana)
region.” There are also two ways in which this data is made accessi-
ble to machines and can therefore be used in an automated way as
part of a library catalog or other discovery tool. The HTML page for
class 945.5 contains structured data in RDFa markup, which means
that user agents will be able to distill caption information as regular
RDF triples.
Another very powerful and flexible way is directly accessing the
triple store using the SPARQL endpoint.
Listing 3: Query that returns all distinct captions associated with class num-
ber 945.5
PREFIX skos:
SELECT DISTINCT ?caption WHERE {
{GRAPH ?g
{?concept skos:notation ’’945.5’’^^;
skos:prefLabel ?caption
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J.S. Mitchell, Dewey linked data
}
}
}
Note that the endpoint supports HTTP bindings of the SPARQL
protocol, meaning that the endpoint serves as a general web service
interface (in case the linked data presentation is not preferred).
DDC-DDC number components links
The second use case is an enhancement of data in dewey.info taken
from the DDC itself: links to Dewey synthesized number compo-
nents. The concept is simple: What if we linked every synthesized
number to its component parts? For example, 641.59455 represents
the cooking of Tuscany (641.59 Cooking characteristic of specific
continents, countries, localities + T2—455 Tuscany [Toscana] region).
The underlying Dewey data includes the MARC 21 765 Synthesized
Number Components field: 765 0# $b641.59 $z2$s 455 $u641.59455
By establishing a link between 641.59455 and T2—455 (represented
as ””$z 2$s 455” in the 765 field and as ”2–455” in the URI string), it
is possible to isolate the geographic facet and use it to foster alterna-
tive approaches to discovery. The potential enhancements to such
discovery is discussed in the next section.
DDC-GeoNames links
Linking Dewey data with GeoNames offers the opportunity to ex-
tend the boundaries of categorization and discovery. Since GeoN-
ames has emerged as not only the dominant source for geographic
coordinates in the linked data space, but also as a leading provider
of identifiers (URIs) for geographic entities, a GeoNames term can
act as a general equivalent or a boundary object for data from dif-
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JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013)
ferent domains that have never been directly mapped to each other.
The linking of two concepts in different schemes or from different
domains to the same GeoNames entity helps to establish a common
”aboutness” of these two terms.
Figure 3 illustrates how a common link to a GeoNames term from a
geographic class in dewey.info and from a New York Times subject
heading for the same geographic area establishes a strong (albeit
implicit and untyped) relationship between these two terms because
both entities are ”about” the same city. Also, by extension it can be
assumed that all articles and other resources indexed with the NYT
heading should be discoverable by the DDC class, therefore adding
to the amount of categorized content that can be retrieved by using
this DDC number in a discovery interaction. Links to datasets like
Figure 3: Links to GeoNarmes.
GeoNames extend the boundaries of DDC classes on a conceptual
level as well. Whereas a traditional mapping between KOS usually
connects entities of the same type (e.g., concepts), linking in the
sense of the Semantic Web can connect different kinds of named/i-
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J.S. Mitchell, Dewey linked data
dentified entities. While a mapping between concepts often operates
with variations of semantic relationships traditionally employed by
thesauri (e.g., broader/narrower, related, whole/part), linking of
different types of entities requires a new set of relationships tailored
to the domain model of the linked dataset or value vocabulary. In
the case of GeoNames, in order to store the links in MARC, we have
to use a traditional mapping relationship. However, in a linked
data version, the SKOS mapping relationships (corresponding to
traditional thesaurus relationships) cannot be used to link Dewey
classes and GeoNames terms, because GeoNames URIs identify a
gn:Feature, which is defined as ”a geographical object” and, being a
subclass of http://schema.org/Place, as an entity with a ”physical
extension.” In other words, GeoNames (like many other ontolo-
gies) does not contain descriptions of or identifiers for concepts of
places; it contains descriptions of and identifiers for the places them-
selves. In such cases, a relationship like foaf:focus should be used,
which ”relates a conceptualisation of something to the thing itself.”
A GeoNames URI identifies a locality, not a concept of a locality.
This operation effectively connects a Dewey concept with a differ-
ent set of relationships, which can be used to present information
seekers compelling tools to identify and select geographic features
for resource discovery. In essence, it opens up a new perspective or
viewpoint on the arrangement of classes in Dewey.
Figure 4 on the facing page shows in parallel two different kinds
of neighborhoods applicable to T2—6626 Niger. The established
Dewey ”neighborhood” shows the class in the context of the DDC
notational hierarchy. Linking this class to its corresponding GeoN-
ames feature, however, allows for reusing GeoNames’ gn:neighbour
relationship and applying it directly to this Dewey class. The right-
hand side shows the concept T2—6626 surrounded by features that
neighbor the country in its foaf:focus in the physical world.
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JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013)
Figure 4: Two views of T2—6626 Niger.
Taking this one step further, linking all geographic Dewey concepts
to GeoNames allows for an on-the-fly switching of the viewpoint as
needed, effectively allowing for transforming the concepts temporar-
ily into features, and, by using inherited properties like geographic
coordinates, placing them on a map (figure 5 on the next page).
Furthermore, DDC classes can utilize more than just relationships
inherited from geographic features. The links allow also for a more
expressive typing of related DDC entities and open the door to
geospatial reasoning over the underlying DDC data. For example,
usually it is not clear whether a Dewey number represents a country
(or another type of entity). But in the above example, the ”inherited”
types allow for basic viewpoint-transgressing queries such as: ”Dis-
play all Dewey numbers that represent countries that are adjacent to
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J.S. Mitchell, Dewey linked data
Figure 5: Blending of Dewey viewpoint and geographic viewpoints.
JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013). Art. #5467 p. 194
JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013)
T2—6626.”
Figure 6 shows another example of transgressing viewpoints. Table
2 is mainly arranged by continents, which means that countries that
span different continents are separated notationally, i.e., they don’t
occupy a contiguous span of Dewey numbers. This may even be
true for cities in these countries, e.g., Istanbul in Turkey occupies
subdivisions of both T2—4 and T2—5. While Dewey provides all
necessary relationships in order to relate the European and Asian
parts of Turkey, they are divided notationally, making it not a simple
task for a discovery system to offer the user a compelling way of
selecting subentities for retrieval. Using the inherited gn:neighbour
relationship, however, makes it easy to display classes about the
European part of Turkey e.g., T2—49618, shown with its Relative
Index terms in yellow) and the Asian part (e.g., T2—5632, shown
with its Relative Index terms in green) together in a geobrowser like
Google Earth using the geographic viewpoint.
Figure 6: Overlaying Dewey classes and Relative Index terms on a map
using properties of linked entries.
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J.S. Mitchell, Dewey linked data
Conclusion
The contents of dewey.info and links to Dewey data have evolved
over time as we have taken advantage of various opportunities for
experimentation. With each addition, we have considered possible
use cases for the additional data. The following statement appears
in the last paragraph of the final report of the W3C Linked Library
Data Incubator Group (2011) :
Linked data follows an open-world assumption: the assump-
tion that data cannot generally be assumed to be complete and
that, in principle, more data may become available for any
given entity.
The schema-less RDF data model allows for a substantial degree of
freedom (compared to the relational database paradigm) in leverag-
ing existing data by enrichment and addition of new connections
almost ad hoc. Our efforts to publish the DDC as a linked data value
vocabulary have taken place in a rich and evolving Dewey ecosys-
tem. Figure 7 shows the current state of translations and versions
published, planned, or under way based on DDC 23 data; where
known, expected publication dates are shown in parentheses. Figure
8 shows the current mappings and crosswalks between the DDC
and other knowledge organization systems.
We expect to continue extending linked DDC data within the rich
environment described in figure 7 on the next page and figure 8 on
the facing page to meet use cases in categorization and discovery.
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JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013)
Figure 7: Editions and versions based on DDC 23.
Figure 8: Mappings and crosswalks to the DDC.
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J.S. Mitchell, Dewey linked data
References
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Need Not Be Miscellaneous: Controlled Vocabularies and Classification in a Web
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events/presentations/2008/ISKO/20080805- deweyskos- panzer.ppt. (Cit. on
p. 181).
Panzer, Michael and Marcia Lei Zeng. “Modeling Classification Systems in SKOS:
Some Challenges and Best-practice Recommendations”. Semantic interoperability
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Seoul: Dublin Core Metadata Initiative and National Library of Korea, 2009. 3–14.
http://dcpapers.dublincore.org/ojs/pubs/article/view/9748. (Cit. on p. 181).
JOAN S. MITCHELL, OCLC.
mitchelj@oclc.org
http://staff.oclc.org/d̃ewey/joan.htm
MICHAEL PANZER, OCLC.
panzerm@oclc.org
http://staff.oclc.org/d̃ewey/michael.htm
Mitchell, J.S., M. Panzer. ”Dewey linked data: making connections with old friends
and new acquaintances”. JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013): Art: #5467.
DOI: 10.4403/jlis.it-5467. Web.
ABSTRACT: This paper explores the history, uses cases, and future plans associated
with availability of the Dewey Decimal Classification (DDC) system as linked data.
Parts of DDC system have been available as linked data since 2009. Initial efforts in-
cluded the DDC Summaries in eleven languages exposed as linked data in dewey.info.
In 2010, the content of dewey.info was further extended by the addition of assignable
numbers and captions from the Abridged Edition 14 data files in English, Italian,
and Vietnamese. During 2012, we will add assignable numbers and captions from
the latest full edition database, DDC 23. In addition to the ”old friends” of different
Dewey language versions, institutions such as the British Library and Deutsche Na-
JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013). Art. #5467 p. 198
http://www.oclc.org/news/events/presentations/2008/ISKO/20080805-deweyskos-panzer.ppt
http://www.oclc.org/news/events/presentations/2008/ISKO/20080805-deweyskos-panzer.ppt
http://dcpapers.dublincore.org/ojs/pubs/article/view/9748
mailto:mitchelj@oclc.org
http://staff.oclc.org/~dewey/joan.htm
mailto:panzerm@oclc.org
http://staff.oclc.org/~dewey/michael.htm
http://dx.doi.org/10.4403/jlis.it-5467
JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013)
tionalbibliothek have made use of Dewey linked data in bibliographic records and
authority files, and AGROVOC has linked to our data at a general level. We expect to
extend our linked data network shortly to ”new acquaintances” such as GeoNames,
ISO 639-3 language codes, and Mathematics Subject Classification. In particular, the
paper examines the linking process to GeoNames as an example of cross-domain
vocabulary alignment. In addition to linking plans, the paper reports on use cases
that facilitate machine-assisted categorization and support discovery in the semantic
web environment.
KEYWORDS: DDC; Dewey linked data; Dewey Decimal Classification
Submitted: 2012-04-25
Accepted: 2012-08-31
Published: 2013-01-15
JLIS.it. Vol. 4, n. 1 (Gennaio/January 2013). Art. #5467 p. 199