# Moving from ISAD(G) to a CIDOC CRM-based Linked Data Model in the Portuguese
Archives

Inês Koch<EMAIL_ADDRESS>0000-0002-9363-9713 Faculty of Engineering of
the University of Porto and INESC TECPortoPortugal ,  Carla Teixeira Lopes
0000-0002-4202-791X Faculty of Engineering of the University of Porto and
INESC TECPortoPortugal<EMAIL_ADDRESS>and  Cristina Ribeiro  0000-0001-6150-0090
Faculty of Engineering of the University of Porto and INESC TECPortoPortugal
<EMAIL_ADDRESS>
###### Abstract.

Archives are facing numerous challenges. On the one hand, archival assets are
evolving to encompass digitized documents and increasing quantities of born-
digital information in diverse formats. On the other hand, the audience is
changing along with how it wishes to access archival material. Moreover, the
interoperability requirements of cultural heritage repositories are growing.
In this context, the Portuguese Archives started an ambitious program aiming
to evolve its data model, migrate existing records, and build a new archival
management system appropriate to both archival tasks and public access. The
overall goal is to have a fine-grained and flexible description, more machine-
actionable than the current one. This work describes ArchOnto, a linked open
data model for archives, and rules for its automatic population from existing
records. ArchOnto adopts a semantic web approach and encompasses the CIDOC
Conceptual Reference Model and additional ontologies, envisioning
interoperability with datasets curated by multiple communities of practice.
Existing ISAD(G)-conforming descriptions are being migrated to the new model
using the direct mappings provided here. We used a sample of 25 records
associated with different description levels to validate the completeness and
conformity of ArchOnto to existing data. This work is in progress and is
original in several respects: (1) it is one of the first approaches to use
CIDOC CRM in the context of archives, identifying problems and questions that
emerged during the process and pinpointing possible solutions; (2) it
addresses the balance in the model between the migration of existing records
and the construction of new ones by archive professionals; and (3) it adopts
an open world view on linking archival data to global information sources.

cultural heritage, archives, archival description, linked open data, semantic
web, data migration

††copyright: acmlicensed††journal: JOCCH††journalyear: 2023††journalvolume:
1††journalnumber: 1††article: 1††publicationmonth: 1††price: 15.00††doi:
10.1145/3605910††ccs: Information systems Digital libraries and archives††ccs:
Information systems Database design and models††ccs: Information systems
Ontologies††ccs: Computing methodologies Ontology engineering††copyright:
acmlicensed††journal: JOCCH††journalyear: 2023††journalvolume:
1††journalnumber: 1††article: 1††publicationmonth: 1††price: 15.00††doi:
10.1145/3605910

© Inês Koch, Carla Teixeira Lopes and Cristina Ribeiro, 2023. This is the
author’s version of the work. It is posted here for your personal use. Not for
redistribution. The definitive Version of Record was published in ACM journals
- Journal on Computing and Cultural Heritage,
http://dx.doi.org/10.1145/3605910.

##  1\. Introduction

National archives are stable institutions by definition. They have to ensure
that their infrastructures and processes can be trusted with our shared memory
for the long term, measured in centuries. Their mission is centered on
preservation: making sure archival assets are kept in the right conditions,
promoting recovery actions for those that become fragile, and keeping the
whole in the best conditions that the available staff and funding allow. They
are, therefore, cautious regarding the adoption of disruptive solutions. On
the other hand, they are confronted with an ever-changing panorama of media,
digital supports (requiring specific technology to access the contents), and
even target audience.

Digital assets are challenging archives in several aspects. They require quite
different infrastructures to be maintained and are not tolerant of so-called
“benign neglect”: unlike traditional materials that degrade continuously and
over long periods, neglect in digital entails inexorable loss. Maintaining
digital assets has required archives to be equipped with vast and safe digital
infrastructures, with the corresponding staff. Also, the transition to digital
creates expectations concerning the digitization of analog supports, a
challenging task given the volumes of information available, and the
brittleness of the treasures kept in the archives. Investments in digital
infrastructure are also hard to plan in the long term, given the pace of
change of digital technologies.

Despite their focus on preservation, archives are more and more responding to
findability and access requirements, namely for laypeople, in quite a shift
from their focus on scholars and specialized access. These requirements have
led to a more systematic view of the archival contents and their organization
according to standards for identification and description. The General
International Standard Archival Description, ISAD(G), has been designed to
deal with extensive collections of heterogeneous objects and adopts a uniform
description to make them manageable. Description can be inherited from a fonds
down to a document series or a single document, making description in large
collections feasible and accommodating uneven description efforts that take
into account the potential for access and reuse.

Access is not the only requirement when people explore an extensive
collection, such as the public archives. The information therein also needs to
be linked to other sources. For example, the biographies of the people
involved may complement the record for an international treaty, and the
toponymic reference in a medieval document may connect to its present-day
location.

In this context, we present the joint effort of a team from Information and
Computer Science and the archival experts from the Portuguese National
Archives. The EPISA project (Entity and Property Inference for Semantic
Archives) is rethinking the existing archival system, assisting in the
transition from the ISAD(G) multilevel description model to a linked data
model used to represent archival information on a prototype open-source
knowledge platform. Current descriptions will be used by Artificial
Intelligence algorithms to extract entities and infer relationships between
those entities. The prototype knowledge graph and corresponding user
interfaces will support applications for specialists and also for the public.

This work describes ArchOnto, a linked open data model for archives, and the
rules for its automatic population from existing records. ArchOnto encompasses
the International Committee for Documentation Conceptual Reference Model
(CIDOC CRM) of the International Council of Museums (ICOM) and additional
ontologies, envisioning interoperability with external sources to build a more
robust user experience. As this is one of the first approaches to use CIDOC
CRM in the context of archives, several problems and questions emerged during
the process that we describe here, and solutions are proposed.

This article is organized as follows. Section 2 has a brief description of the
Portuguese National Archives, presents and compares the main description
standards in cultural heritage, reports on existing applications of CIDOC CRM
in the context of museums and archaeology, and describes works focused on
migration between description standards. In Section 3 we detail ArchOnto and
its development. To validate the appropriateness of ArchOnto with existing
data, we manually represented a sample of 25 records, an experiment described
in Section 4. Based on this experiment, we produced a set of rules, detailed
in Section 5, that are currently being used in the first stage of the
migration process. We finish with a discussion of results in Section 6 and
present our main conclusions in Section 7.

##  2\. Background and State of the Art

Cultural heritage institutions have pioneered the definition of standards for
resource description, in line with the missions of libraries, archives, and
museums. They evolved as specialized, dedicated resources and have been to
some extent adopted in the more flexible web-age models for resource
description (Weibel and Koch, 2000). The Portuguese National Archives have
long adopted the ISAD standards and built a dedicated archival information
system to support their operation, including interfaces for archivists and for
the web, while keeping record of conservation activities and the management of
the physical location of assets and the reading rooms.

###  2.1. Portuguese Archives

The General Directorate for Book, Archives, and Libraries (DGLAB) is a public
body under the responsibility of the Portuguese Ministry of Culture. This
structure comprises two national archives (Torre do Tombo National Archive -
ANTT - and the Portuguese Center of Photography), the Overseas Historical
Archive, and 16 regional archives at the district level (DGLAB, 2008). Torre
do Tombo is one of the oldest national archives in the world and one of the
oldest institutions in Portugal. The ANTT curates a unique collection of
historical and contemporary objects that were accumulated since the 9th
century.

DigitArq (Ramalho and Ferreira, 2004) is a custom platform commissioned by the
National Archives and is currently used for archival description by the DGLAB.
DigitArq also provides public access to online services and is available at
https://digitarq.arquivos.pt/. Remotely, users can access the archives, look
at scanned documents, request digital reproductions, book documents for in
loco examination, or request certificates.

DGLAB has about 2.8 million records, most of them under the custody of ANTT.
The oldest records were produced in the 9th century, and the number of records
has been steadily growing over time. Fonds are organized in groups, such as
Central and Local Administration; Collections; Companies; Judicial; Monastics;
Notaries; Parish; and Personal. Collections include records from Estado Novo,
Portugal’s Ancien Régime; records from contemporary, ecclesiastical, monastic
and conventual institutions; records of archives of individuals, families,
associations, companies, commissions and congresses; and records of
photographic archives.

Most of the records (about 1.4 million) are in Portuguese, and the second
language is Spanish, with 30.8 thousand records. As expected, the number of
records with a digital representation has been growing in the last decade. The
main format used for these is tiff, followed by jpg and pdf. As expected, the
most common levels of description are the ‘file’, corresponding to compound
documents in DigitArq, with 1.75 million records, and ‘item’, used for simple
documents, with 0.8 million records. Regarding the elements of description,
the ones with a large median for the number of characters are the
‘Biographical History’, followed by the ‘Finding Aids’, ‘Related Units of
Description’ and ‘Scope and Content’.

###  2.2. Standards for Description in Cultural Heritage

The International Council on Archives (ICA) is responsible for the development
of the ISAD(G) General International Standard Archival Description
(International Council on Archives, 2016), a widely adopted standard. It is
characterized by a multilevel structure that allows description to proceed
from general to specific, representing each fonds’ context, hierarchical
structure and components. The second edition of the standard dates from 2000
and includes general guidelines for the preparation of archival descriptions.
ISAD(G) was the basis for the development of the Encoded Archival Description
(EAD), a standard maintained by the Society of American Archivists and the
Library of Congress (Pitti, 1999). The EAD is an XML language that is used as
an interoperability layer between the archival standards and the technological
platforms supporting them.

More recently, ICA started developing a new data model that builds on the
concept of linked open data — RiC-CM. This new model was developed considering
data models developed by archival communities in several countries, namely
Australia, Spain and Finland.

The Australian Government Recordkeeping Metadata Standard (AGRkMS) includes
information about records and the contexts where they are captured and used
(National Archives of Australia, 2015). The latest version (2.2) was issued in
2005 to revise the first version, dating from 1999. This standard includes the
minimum metadata necessary to ensure that records remain accessible and usable
over time. It also comprises the metadata needed to manage the preservation of
digital records for ongoing agency business needs and metadata for records
held in a digital archive (National Archives of Australia, 2015).

In Spain, the Comisión de Normas Españolas de Descripción Archivística (CNEDA)
has developed Modelo Conceptual de Descripción Archivística y Requisitos de
Datos Básicos de las Descripciones de Documentos de Archivo, Agentes y
Funciones (MCDA) – Conceptual Archival Description Model and Basic Data
Requirements for the Descriptions of Archival Records, Agents and Functions.
In this conceptual model of archival description, the types of entities
(record, agent, role, standard, concept, object or event, location) are
presented, as well as the relationships between entities of these types, and
the attributes of three types of entities (record, agent, role) (Comisión
Normas Españolas de Descripción Archivística, 2012).

In Finland, the Finnish Conceptual Model for Archival Description, presented
from here on as FCMAD, was developed for archival description and consists of
an ontological conceptual model and metadata models, implementing the
conceptual model in practice. The model, developed by the National Archives of
Finland (Arkistolaitos), advocates separate models for the main description
entities, along with the relations that hold between them. It recognizes a set
of entities: function, agent, manifestation, expression, item, information
resource, life cycle, mandate (norm), place, time, and subject (Llanes-Padrón
and Pastor-Sánchez, 2017).

The goal of the Records in Contexts Conceptual Model (RiC-CM) (International
Council on Archives, 2016) is to reconcile, integrate, and build on four
previous ICA standards: ISAD(G); the International Standard Archival Authority
Records — Corporate Bodies, Persons, and Families (ISAAR(CPF)); the
International Standard Description of Functions (ISDF); and the International
Standard Description of Institutions with Archival Holdings (ISDIAH). In July
2021, ICA released a full version of the 0.2 version of this model and, in
February 2021, the 0.2 version of the Records in Contexts Ontology.

The CIDOC Conceptual Reference Model (CIDOC CRM) (ICOM/CIDOC CRM Special
Interest Group, 2019) was developed in the scope of museums by the
International Committee for Documentation (CIDOC) of the International Council
of Museums (ICOM). This model, which aims to exchange, mediate, and integrate
heterogeneous sources of information related to cultural heritage, is under
active development by the CIDOC CRM Special Interest Group (CIDOC CRM SIG).
The CIDOC CRM went through several changes over the years, and it became an
ISO standard in 2006 (ISO 21127), with a revision in 2014 (ISO 21127: 2014).
At present, CIDOC CRM is the only ontology in the Cultural Heritage domain to
have this official status, recognizing its acceptance in the community and
contributing to reinforce it (Bruseker et al., 2017). It has a strong emphasis
on events and is also quite detailed concerning the representation of people,
places, and time periods, concepts that are quite central in archival
description.

In libraries, the International Federation of Library Associations and
Institutions (IFLA) developed the Functional Requirements for Bibliographic
Records (FRBR), with two main goals. The first is to provide a clearly defined
structure for relating the data in the bibliographic records to the users’
needs. The second is to recommend a basic level of functionality for records
created by national bibliographic institutions (IFLA Study Group, 2009).

Table 1 provides a high-level view of some features of ISAD(G), RiC-CM, CIDOC
CRM, AGRkMS, MCDA, and FCMAD. We exclude FRBR due to its smaller expression in
the context of archives. The ICA, Australian, Spanish, and Finish models
consider the hierarchical structure intrinsic to the archives. CIDOC CRM, RiC-
CM, AGRkMS, MCDA, and FCMAD comply with semantic web principles and,
therefore, aim to represent cultural heritage data as linked data. While the
ISAD(G) standard has a limited number of elements, some of which have values
that can be quite complex, the more recent models have a number of properties
an order of magnitude larger, attesting to their more atomized representation
of knowledge. All models have institutional supervision in the corresponding
working groups under well-established cultural heritage institutions. While
ISAD(G) has been supported in various archival information systems over the
years, the RiC-CM still lacks the test of actual deployment. Concerning the
models developed by national institutions, these have already been applied in
the corresponding archives.

Table 1. Standards Comparison | ISAD(G) | RiC-CM | CIDOC CRM | AGRkMS | MCDA | FCMAD
---|---|---|---|---|---|---
Hierarchical | ✓ | ✓ | x | ✓ | ✓ | ✓
LOD | x | ✓ | ✓ | ✓ | ✓ | ✓
Ontology | x | ✓ | ✓ | N/A | N/A | ✓
Number of properties | x | 449 | 285 | 70 | N/A | 16
Number of elements | 26 | x | x | x | x | x
Supervising institution | ICA | ICA | ICOM | NAA | CNEDA | Arkistolaitos
Years of institutional supervision | +25 years | +5 years | +25 years | +15 years | +10 years | +5 years
Implementation on archives | Custom | None | (none known) | Australia | Spain | Finland
Most recent version | 2000 | 2021 | 2021 | 2015 | 2012 | 2013
Support group | ICA | ICA(EGAD) | CIDOC CRM SIG | NAA | CNEDA | Arkistolaitos
N/A – Not Publicly Available; NAA – National Archives of Australia

###  2.3. Applications of CIDOC CRM

Due to its maturity, CIDOC CRM has already been adopted in several areas of
knowledge. In the scope of museums, the model was adopted by the Museo del
Prado (Bravo et al., 2016) and the British Museum (Bruseker et al., 2017). In
addition to museums, the model was used in archaeology, namely, in the Ariadne
Project (ARIADNE, 2014), in music through the DOREMUS Project (Achichi et al.,
2018) and EthnoMuse (Strle and Marolt, 2012), and in archives through the ICON
(de Almeida and Runa, 2018) and EPISA (Koch et al., 2020) projects.

In Madrid, Spain, the Museo del Prado developed a knowledge graph that is
based on a broad group of ontologies from several domains, integrating them
into a shared framework or ontological narrative representing the overall
group of activities taking place in the museum setting (Bravo et al., 2016).
Among these activities are the documentation associated with conservation
processes, the communication with the media, and the online sale of objects
from the Prado store. The main entities in the Prado semantic network, namely
Work of Art, Author, Exhibition, and Activity (Lara-Clares et al., 2017), are
represented according to the CIDOC CRM standard. The FRBR ontology was adopted
to represent bibliographic records. The Museum has identified other concepts
relevant to its activity, namely those concerning news, the regulations for
contracts in the public sector, and human resources. For each of these areas,
existing ontologies were adopted and brought together with CIDOC CRM and FRBR
in the Digital Semantic Model for the museum111Website Museo del Prado -
Digital Semantic Model – last consulted on 10/01/2022 – Available at
https://www.museodelprado.es/modelo-semantico-digital/modelo-ontologico.

In the British Museum, the first arts organization in the United Kingdom to
publish its collection semantically, CIDOC CRM is used to establish links with
other institutions222Website The National Archives – last consulted on
10/01/2022 – Available at:
https://webarchive.nationalarchives.gov.uk/20170803104533/http://www.britishmuseum.org/about_us/news_and_press/press_releases/2011/semantic_web_endpoint.aspx.

The purpose of the semantic model at the British Museum is to provide a new
degree of accessibility, while allowing others to work closely with the data,
obtain new insights and produce innovative applications (Oldman, 2014). This
semantic model was developed in the scope of the Research Space Project, a
project that has built the integrative data infrastructure for the web
presence of the collections of the British Museum (Bruseker et al., 2017).

In archeology, extensions to CIDOC CRM, namely CRMba and CRMarchaeo were
proposed. The former intends to model the complexity of a built structure from
the perspective of the archaeology of buildings, while the latter was
developed to model the processes involved in investigating subsurface
archaeological deposits (Ronzino, 2017). At the European level, the Advanced
Research Infrastructure for Archaeological Dataset Networking in Europe
(ARIADNE) project stands out in the area of archeology. The ARIADNE data
portal uses the CIDOC CRM to implement archaeological interoperability at a
conceptual level. This project is also contributing to the development of
CRMarcheo, the archaeological extension of CIDOC CRM aimed at deep data
integration (ARIADNE, 2014).

Also in the archeology domain, the Arches Project was designed to take
advantage of the CIDOC CRM approach to create meaningful data relationships
between heritage resources and groups, activities, actors, events, and
information media (Group, 2021). It is an open-source software platform
developed jointly by the Getty Conservation Institute and World Monuments Fund
for cultural heritage data management (Trust and Fund., 2021).

In music, CIDOC CRM was used in the DOREMUS Project to semantically describe
the catalogs of musical works and events of three French institutions — the
French National Library (BnF), Radio France, and the Philharmonie de Paris.
One significant contribution of this project was the creation of the DOREMUS
Ontology, which extends the CIDOC CRM and FRBRoo models to represent
bibliographic information, adapting it to the domain of music (Achichi et al.,
2018).

CIDOC CRM and the FRBRoo were also used in the EthnoMuse digital library to
represent processes and relations in folk song and music realizations. The
EthnoMuse digital library consists of novel tools and techniques that assist
with digitizing the Institute of Ethnomusicology collections. These support
the ongoing production and post-production processes related to field
recordings and documentation of Slovenian folk song music and dance, to enable
the manipulation and search of the library’s contents (Strle and Marolt,
2012).

In the archives, CIDOC CRM was used in two interlinked projects, ICON and
EPISA. These two projects, developed by a multidisciplinary group, use CIDOC
CRM to represent archival records and aim to build a new archival technical
data infrastructure suited to archival specialists and to external users (de
Almeida and Runa, 2018). Although the RiC-CM is being developed in the
archives, at the beginning of the development of these projects, in 2018, it
was still at a preliminary stage, which led to the choice of the CIDOC CRM
which was already in a more mature stage of development (Koch et al., 2020).

###  2.4. Semantic mapping of description standards to CIDOC CRM

The increasing demand for global search, comparative studies, and data
migration between heterogeneous sources of cultural contents requires the
semantic interoperability of CIDOC CRM with other description standards
(Doerr, 2003).

A semantic mapping of the EAD to CIDOC CRM is one of the first approaches to
such interoperability (Theodoridou and Doerr, 2001). More specifically, this
maps the EAD Document Type Definition (DTD) elements to CIDOC, showing their
representation in the CIDOC CRM ontology both visually and through formal
rules.

A more recent work also focuses on the mapping between EAD and CIDOC CRM
(Bountouri and Gergatsoulis, 2011). It proposes the semantic organization of
an archive in 3 hierarchies: physical, informational, and linguistic. The
mapping of EAD elements and attributes follows from this organization and is
expressed in the Mapping Description Language (MDL).

The semantic integration of CIDOC CRM with Dublin Core has also been studied
(Lourdi et al., 2009). It consists of a path-oriented crosswalk from Dublin
Core Collections Application Profile (DCCAP) to CIDOC/CRM ontology and vice
versa. The conclusion is that the mapping is complex, given the event-based
character of CIDOC/CRM that requires the use of intermediate activity and
event entities.

##  3\. ArchOnto

Modeling ontologies through the adoption of existing ontologies, builds on
others’ work and experience, promotes interoperability and is inline with the
ideas promoted by the semantic web. CIDOC CRM is a stable model, accepted as
an international standard and with ongoing work with the library community. By
the time this work started, the model had already been explored by the
specialists at DGLAB, and therefore it provided a common language for the
project team.

ArchOnto is the name of the new model supporting the representation of assets
at DGLAB. Its goal is to serve as the foundation for the development of a
knowledge graph prototype and new applications for the archives.

###  3.1. Development process

With CIDOC CRM as the basis for the development of the data model for the
archives, we did an in-depth study of the standard. We considered the broad
set of concepts in CIDOC CRM to represent the information in existing records
in DigitArq, which are described with the ISAD(G) standard. Many essential
concepts in archives are well established in digital humanities, and therefore
already present in CIDOC CRM. Others are specific to the domain of the
archives and have no direct representation in CIDOC CRM. An example is the
Level of Description, specific to the hierarchical representation of ISAD(G),
a mandatory element in existing records, and one that we intend to maintain in
the new model.

As we recognized that CIDOC CRM alone would not provide the expressiveness for
all the fundamental concepts in archives, we considered extensions or other
ontologies. The ArchOnto data model333OWL version available on GitHub -
ArchOnto2021: https://github.com/feup-
infolab/archontology/tree/master/ArchOnto_2021 emerged. At first, Archonto
included CIDOC CRM and some extensions, but it soon became clear that we
should integrate separate ontologies instead of extensions in some situations.
Distinct ontologies make it easy for an ontology created specifically for this
model to be replaced by a reference ontology with the same purpose, taking
advantage of new developments as they appear.

Beyond the separate ontologies, ArchOnto includes some extensions to CIDOC
CRM, such as a set of subclasses of E55 Type. This class is the entry point
for the representation of categories of objects for which the archives use
controlled vocabularies. Without the subclasses, E55 Type would be used for
such diverse types as an identifier type, taking values such as reference code
or physical location, or a name type, instantiated as first name, surname,
nickname. The use of E55 Type for the whole range of such types in the
archives would not allow additional control on the used vocabularies, and
therefore subclasses were created. For each subclass, the instances will be
determined by existing vocabularies for the corresponding type. Table 8, in
Appendix A, shows that we followed the same logic in the creation of
subclasses for E35 Title, E39 Actor, and E54 Dimension.

###  3.2. ArchOnto Architecture

ArchOnto is presented as a modular data model that integrates five ontologies,
dealing with complementary aspects of the archival domain, as illustrated in
Figure 1. The five ontologies are CIDOC CRM (base ontology), N-ary,
DataObject, ISAD Ontology, and Link2DataObject. Figure 1 also shows ArchOnto’s
classes and properties and their relation with other ontologies.

Figure 1. ArchOnto architecture. ARP12 has level of description is a
subproperty of CIDOC CRM P2 has type property.

CIDOC CRM is the core of ArchOnto, providing the concepts and properties to
capture archival records’ essential features, e.g. event, date, location,
person, group. Figure 2 shows the CIDOC CRM classes and properties that are
most likely to be used to represent an archival record, that typically has
information such as the title, language, document identifiers, and their
dimension and support.

Figure 2. Outstanding CIDOC CRM classes and properties in ArchOnto

The N-ary ontology provides a systematic way to represent non-binary
associations, i.e., those that connect more than two individuals. Representing
a person’s role in a given event is an example of this kind of association
because it involves relating an event, a person, and a role. N-ary takes into
account the CIDOC CRM recommendations444http://www.cidoc-
crm.org/sites/default/files/Roles.pdf for the representation of tuples with
arity higher than two. In ArchOnto, this is modeled as a complementary
ontology that follows the recommendations of CIDOC. As a separate ontology, it
is easier to replace it or even dismiss it in case CIDOC CRM evolves to
include these concepts. Figure 1 illustrates the classes and properties used
in the N-ary ontology. Tables 8 and 9, in Appendices A and B, show how the
classes and properties from N-ary fit in the ArchOnto’s hierarchy.

DataObject is an auxiliary ontology created to deal with literal values and
their validation in ArchOnto. The goal is for each individual that has a
representation as a simple type, such as a date or a string, to be validated
based on the corresponding class. DataObject comprises classes and data
properties for the simple types in the ontology. These classes and properties
are illustrated in Figure 1 and more systematically in Appendices A and B. In
this ontology, the names of classes are preceded by DOE (from DataObject
Entity), and the names of properties are preceded by DOP (from DataObject
Property).

The ISAD Ontology was designed to take into account the archival practice in
legacy records and to facilitate the migration of such records. CIDOC CRM, and
therefore ArchOnto, has more fine-grained information than the existing
records. In parallel with the evolution of the model and the archival
applications, the creation of new records by the experts will comply with this
increased granularity. In the migration process, textual elements from
existing records are mined to extract relevant information for populating the
new model. This extraction, albeit successful, will generate text fragments
that can hardly convey the full meaning of the existing text. The ISAD
Ontology matches the ISAD(G) standard elements that can be directly obtained
from existing records. The information is represented in this ontology with
Data Properties and is not atomized (as shown on Table 9, in Appendix B). The
ontology can be regarded as an intermediate representation for legacy records,
making it possible, whenever necessary, to check the contents of a given
element against the information extracted thereof. The ISAD Ontology will only
be used for the existing records in DigitArq and not for newly created records
based on ArchOnto.

Finally, the Link2DataObject ontology makes the connection between the CIDOC
CRM and the DataObject ontologies (Table 9). It has a single property to make
this connection — _L2DO hasValue_. Link2DataObject is separated from
DataObject for practical reasons: if another ontology replaces DataObject, the
link to the CIDOC CRM is still required.

In addition to these five imported ontologies, ArchOnto has its classes and
properties, created as extensions to CIDOC CRM. Classes are used to specialize
concepts already present in CIDOC CRM but which needed to be adapted to
include controlled vocabularies that exist in the archives. Figure 1 and Table
8 in Appendix A show the classes that are part of this ontology and how they
relate to CIDOC CRM. In addition to these classes, the ontology also includes
three properties. ARP12 has level of description relates a given document to
its level of description. ARP8 upper level and ARP9 lower level (inverse of
each other) relate a level of description with the upper (respectively lower)
levels where it may be aggregated (aggregate). This provides a control
structure for the admissible nesting of units of description. Names for
classes are preceded by ARE (from ARchival Entity), and those for properties
are preceded by ARP (from ARchival Property).

To facilitate and validate the population of ArchOnto, we have defined
controlled vocabularies that can be used in one or more classes. As an
example, we present some of these vocabularies in Table 2, along with the
classes and example values.

Table 2. Controlled vocabularies Class | Vocabulary | Example Values
---|---|---
ARE1 Level of Description | Level of description | Fonds; Series; Section; File; Item
| ARE2 Formal Title
---
ARE3 Supplied Title
Title Type | Formal, Supplied
ARE5 Identifier Type |  | Identifier of collective
---
person/group
| PT; VCT; AGH01; 161016; ADLSB;
---
600084892; PT-LiBN
| ARE6 Date Type
---
ARE9 Date Certainty
Type of time period |  | Exact dates; Inferred dates; Predominant
---
dates
ARE7 Name Type |  | Type of name of collective
---
person/group
| Authorized form of name; Another form of
---
the name; Parallel name form
ARE8 Role Type | Role played | Producer; Material Author; Recipient
ARE11 Documentary Typology | Documentary Typology | Certificate; Income book; Patent
ARE13 Subject Type | Subject | Education; Science; Law; Management
ARE14 Place Type | Type of jurisdictional entity |  | Ocean; Archipelago; Mountain range;
---
Country; District
ARE15 Acquisition Type |  | Transfer of Custody /
---
Acquisition Identifier
| Purchase; Giving; Donation; Deposit;
---
Swap; Legacy; Reintegration; Transfer
ARE16 Event Type | Event Type | Evaluation; Expertise; Financial management
E56 Language | Language Identifier | Portuguese; Latin; French; Greek
E57 Material | Support | Paper; Parchment; Photosensitive film
E58 Measurement Unit | Measurement Unit | Centimeter; Gram; Byte; Minute; Pack
E98 Currency | Currency | Euro; Dollar; Kwanza

##  4\. Manual Representation

The Portuguese National Archives hold a vast number of cultural objects. To
validate the appropriateness of ArchOnto with existing data, we manually
represented a sample of records. In Section 4.1 we describe this sample and
how it was obtained.

A manual representation process was then performed for the record sample,
according to the data model. The representation process ran in an iterative
way. The representation of the records was carried out for subsets of five
records, and the representation for each subset was discussed with the
archival specialists. We manually introduced all individuals and property
instances in Protégé, the tool used to develop the ontology. Due to space
restrictions, in this paper’s context, we only include ArchOnto’s
representation of one of the records (see Section 4.2). The complete set of
representations is available as supplemental material 555Available at:
https://github.com/feup-
infolab/archontology/tree/master/ArchOnto2021_25records.

###  4.1. Sample

Experts of the Portuguese National Archives selected twenty-five records
representative of the various description levels and groups of fonds. These
records are listed in Table 3 and include ten records at different levels of
description within the same fonds plus fifteen records of representative
groups of fonds.

In the record sample, some documents are relevant to the Portuguese cultural
heritage. In the documents of the Juízo da Índia e Mina fonds, for instance,
there are records related to the Ultramar (former Portuguese colonies),
providing evidence of processes related to the commercial routes used, as well
as the products that were marketed, the ships and their types. In addition,
records from representative classes include those relating to monastic,
personal, notary, and central administration documents.

Table 3. Records in Sample. Title | Reference Code | LD | Group of Fonds | Dates
---|---|---|---|---
Juízo da Índia e Mina | PT/TT/JIM | Fonds | CA | 1700-1833
Autos cíveis de petição […] | PT/TT/JIM/A/0001/00001 | File | CA | 1806-1806
Juízo das Justificações […] | PT/TT/JIM-JJU | Subfonds | CA | 1700-1833
Cartório do escrivão Lino […] | PT/TT/JIM/E | Section | CA | 1809-1811
Oriente | PT/TT/JIM-JJU/004 | Serie | CA | 1749-1833
Maço 5 | PT/TT/JIM-JJU/003/0005 | IU | CA | 1765-1828
Autos de sentença de […] | PT/TT/JIM-JJU/003/0005/00008 | File | CA | 1816-1817
Extrato do jornal a […] | PT/TT/JIM/JJE/0001/00038 | Item | CA | 1813-07-12
Procuração de Vasco […] | PT/TT/JIM/JJE/0002/00035 | Item | CA | 1803-01-21
Acção cível de fretes […] | PT/TT/JIM/A/0008/00012 | File | CA | 1803
”Venda de louça preta […]” | PT/TT/EPJS/SF/008/10253 | Item | Companies | 1917
Mosteiro de São Bernardo […] | PT/ADPTG/MON/MSBP | Fonds | Monastics | 1443-1882
Gabinete da Área de Sines | PT/ADSTB/AC/GAS | Fonds | CA | 1941-2006
Carta de Antão Santos […] | PT/ADCTB/PSS/APASC/00001 | Item | Personal | 1937-09-23
Registo de passaportes deferidos | PT/ADBGC/AC/GCBGC/PAS/077/01140 | IU | DCA | 1844-1858
”Um aquário de 2,40x1,00 m” | PT/TT/AS/A/001/000142 | Item | Personal | 1913-04-18
Testamento | PT/ADAVR/NOT/CNVFR2/002/0001/000007 | Item | Notary | 1903-08-26
Planta de parte do 3.º […] | PT/PNA/DGFP/0002/0001/00047/00002 | Item | CA | 1914
Carta náutica, de João […] | PT/TT/CRT/198 | Item | Collections | 1620-1640
Bula ”Romani Pontificis” […] | PT/TT/BUL/0003/06 | Item | Collections | 1523-03-12
Processo de Jerónima da Cruz | PT/TT/TSO-IE/021/00203 | File | CA | 1547-03-12
Desembargo do Paço | PT/TT/DP | Fonds | CA | 1610-1833
Inventário por óbito de […] | PT/ADPRT/JUD/TCVNG/077/00053 | File | Judicial | 1973-1974
Registo de batismo | PT/ADBJA/PRQ/AJT01/001/0013 | IU | Parish | 1862
Notas para escrituras diversas | PT/ADSTR/NOT/07CNABT/001/0023 | IU | Notary | 1703
LD, IU, CA, and DCA stand for Level of Description, Installation Unit, Central
Administration, and Decentralized Central
Administration, respectively.

###  4.2. Representation of “Juízo da Índia e Mina”

We focus here on the representation of the first record in the sample, “Juízo
da Índia e Mina”, with PT/TT/JIM as reference code – Figure 3. This is a Unit
of Description at the level of the fonds, and has information that pertains to
all documents in the fonds. This record has, therefore, a description with
substantial detail. The ISAD(G) elements that constitute the record have
information that translates directly to ArchOnto individuals and properties,
and other information that needs to be atomized to become part of the ArchOnto
representation. We started with the ISAD(G) elements that have a direct
representation in the new model.

Figure 3. Representation example of “Juízo da Índia e Mina”.

The record we are representing is the description of a document, and the
document as a whole is present as an object of the E31 Document class. Note
that “Document” will be used for Units of Description (UD) at different levels
in the archives hierarchy, namely the fonds level in this example. In ISAD(G),
UD is an abstract concept, used for units at different levels and “Document”
is a specific level, while in CIDOC CRM parlance all UD correspond to
documents with different levels of aggregation.

The first ISAD(G) element to be considered is the Level of Description,
represented in ArchOnto through the ARE1 Level of Description class. This
class is a subclass of E55 Type and is associated with a document (E31
Document) through the property ARP12 has level of description.

The document title is the next core element represented through ArchOnto. In
the example, the document title is a supplied title, and an object of class
ARE3 Supplied Title is used to represent the title. This class, a subclass of
E35 Title, indicates the type of title used in the document record. In
addition to this type of title, assigned by an archivist, in ArchOnto, it is
possible to represent a formal title, originated in the document – ARE2 Formal
Title. The representation of the title also uses the DOE8 String class of the
DataObject ontology to define and validate the actual string of characters in
the title.

One of the main identifiers of a document in ISAD(G), the reference code, is
also represented in ArchOnto, through the class E42 Identifier, which links to
the document through the property P1 is identified by. ISAD(G) allows several
kinds of identifiers. The fact that this is a reference code is visible in the
association to an object of the ARE5 Identifier Type class. ARE5 is a subclass
of E55 Type and is linked to E42 Identifier through the property P2 has type.

In Figure 3, it is also possible to observe the representation of the
dimension and support of the document, which originated in the representation
of the physical documents owned by the ANTT. Archival objects include several
kinds of documents, in digital or physical format. The latter may or may not
have associated digital representations. As these ISAD(G) elements concern the
physical part of the document, they are linked to the document via an instance
of the E22 Human-Made Object class. The document support is represented with
class E57 Material and is linked to the physical object through the property
P45 consists of. On the other hand, the dimension is represented by E54
Dimension and has two associated values, the dimension measurement unit — E58
Measurement Unit — and its value. These two values are linked to the dimension
through properties P91 has unit and P90 has value, respectively.

In addition to the physical document properties, there is ISAD(G) information
regarding the corresponding conceptual object, which is represented in Figure
3 through the E33 Linguistic Object class. In this figure, we have the
representation of the creation date of the description of the archival
document. Several classes are necessary to validate the data. The date
representation starts with the presentation of the creation event of the
archival record (E65 Creation), followed by two different E52 Time-Span, one
for the creation of the record and the other to express the last modification.
The time-span has an appellation (E41 Appellation) that is composed of an
DOE10 Instant. In the Instant, with a timestamp, the date is typed and
validated through the DataObject. The dates have a format complying with the
dateTime datatype — xsd: dateTime, with pattern “YYYY-MM-DDThh:mm:ss”.

The complete information in the ISAD(G) elements for this fonds is captured,
in this representation, with the ISAD Ontology. This is a simple, auxiliary
ontology, where the textual elements are kept whole for migrated records. For
simplification purposes, in Figure 3, we only show the representation of the
title and publication notes.

Information from more verbose ISAD(G) elements will also be atomized in
ArchOnto. To this end, several ArchOnto classes were identified, capturing
concepts that are present in the ISAD(G) elements, including events (E5
Event), people (E21 Person), places (E53 Place) and kinds of ships (E55 Type).

###  4.3. Properties and classes used in the manual representation

With the representation of selected records, it was possible to observe the
relative use of the classes and properties in ArchOnto. Table 4 and Table 5
provide the number of times each class and property was used in the manual
representation of the 25-record sample.

Table 4. Occurrences of classes in the migration of the sample records

Ontology | Classes | Nr
---|---|---
CIDOC CRM | E41 Appellation | 247
DataObject | DOE8 String | 209
CIDOC CRM | E52 Time-Span | 106
CIDOC CRM | E42 Identifier | 70
CIDOC CRM | E31 Document | 69
CIDOC CRM | E21 Person | 63
CIDOC CRM | E22 Man-Made Object | 61
DataObject | DOE17 PersonName | 53
DataObject | DOE11 Interval | 52
DataObject | DOE10 Instant | 49
CIDOC CRM | E53 Place | 45
N-Ary | PC14 Carried Out By | 45
ArchOnto | ARE3 Supplied Title | 38
CIDOC CRM | E35 Title | 33
CIDOC CRM | E54 Dimension | 32
ArchOnto | ARE8 Role Type | 30
CIDOC CRM | E74 Group | 30
ArchOnto | ARE11 Documentary Typology | 25
CIDOC CRM | E12 Production | 25
CIDOC CRM | E33 Linguistic Object | 25
CIDOC CRM | E65 Creation | 25
CIDOC CRM | E7 Activity | 21
CIDOC CRM | E55 Type | 19
CIDOC CRM | E32 Authority Document | 13
CIDOC CRM | E57 Material | 13

Ontology | Classes | Nr
---|---|---
CIDOC CRM | E58 Measurement Unit | 12
CIDOC CRM | E67 Birth | 9
ArchOnto | ARE1 Level of Description | 8
ArchOnto | ARE2 Formal Title | 8
CIDOC CRM | E3 Condition State | 8
CIDOC CRM | E10 Transfer of Custody | 8
CIDOC CRM | E56 Language | 8
ArchOnto | ARE6 Date Type | 5
CIDOC CRM | E66 Formation | 5
ArchOnto | ARE5 Identifier Type | 4
CIDOC CRM | E5 Event | 4
ArchOnto | ARE4 Extension | 3
ArchOnto | ARE14 Place Type | 3
ArchOnto | ARE15 Acquisition Type | 3
CIDOC CRM | E68 Dissolution | 3
ArchOnto | ARE9 Date Certainty | 2
ArchOnto | ARE16 Event Type | 2
CIDOC CRM | E69 Death | 2
ArchOnto | ARE13 Subject Type | 1
DataObject | DOE9 Approximate | 1
CIDOC CRM | E9 Move | 1
CIDOC CRM | E36 Visual Item | 1
CIDOC CRM | E85 Joining | 1
CIDOC CRM | E86 Leaving | 1
CIDOC CRM | E96 Purchase | 1

Table 5. Occurrences of properties in the migration of the sample records

Ontology | Property | Nr
---|---|---
DataObject | DOP7 string value | 418
CIDOC CRM | P1 is identified by | 313
CIDOC CRM | P2 has type | 223
DataObject | DOP5 name | 106
DataObject | DOP2 end date value | 102
DataObject | DOP6 start date value | 102
CIDOC CRM | P4 has time-span | 101
DataObject | DOP8 timestamp | 98
CIDOC CRM | P70 documents | 86
CIDOC CRM | P102 has title | 79
CIDOC CRM | P3 has note | 74
CIDOC CRM | P90 has value | 70
CIDOC CRM | P14.1 in the role of | 49
ArchOnto | ARP12 has level of description | 48
CIDOC CRM | P67 refers to | 47
N-Ary | P01 has domain | 47
ISAD Ontology | ISAD9 has scope | 36
CIDOC CRM | P43 has dimension | 35
CIDOC CRM | P91 has unit | 34
CIDOC CRM | P128 is carried by | 33
CIDOC CRM | P45 consists of | 32
CIDOC CRM | P72 has language | 30
CIDOC CRM | P106 is composed of | 27
CIDOC CRM | P94 was created by | 25
CIDOC CRM | P108 was produced by | 25
N-Ary | P02 has range | 23
CIDOC CRM | P107 has current or former […] | 20
ISAD Ontology | ISAD10 has conditions […] | 18
ArchOnto | ARP8 upper level | 16
ArchOnto | ARP9 lower level | 16
ISAD Ontology | ISAD18 has note | 16
CIDOC CRM | P130 features are also found on | 15
CIDOC CRM | P46 is composed of | 14
ISAD Ontology | ISAD15 has related unit of […] | 14
ISAD Ontology | ISAD7 has administrative […] | 12
ISAD Ontology | ISAD19 has system of […] | 12
ISAD Ontology | ISAD24 has conditions […] | 12
CIDOC CRM | P11 had participant | 11
CIDOC CRM | P89 falls within | 11
CIDOC CRM | P129 is about | 11
CIDOC CRM | P7 took place at | 10
CIDOC CRM | P98 brought into life | 10

Ontology | Property | Nr
---|---|---
ISAD Ontology | ISAD8 has archival history | 10
ISAD Ontology | ISAD25 has conditions governing use | 10
ISAD Ontology | ISAD26 has immediate source of […] | 10
CIDOC CRM | P14 carried out by | 8
CIDOC CRM | P28 custody surrendered by | 8
CIDOC CRM | P29 custody received by | 8
CIDOC CRM | P30 transfered custody of | 8
CIDOC CRM | P97 from father | 8
ISAD Ontology | ISAD16 has existence and location […] | 8
ISAD Ontology | ISAD17 has publication note | 8
CIDOC CRM | P74 has current or former residence | 6
CIDOC CRM | P96 by mother | 6
ISAD Ontology | ISAD20 has physical characteristics […] | 6
CIDOC CRM | P5 consists of | 5
CIDOC CRM | P12 was present at | 5
CIDOC CRM | P95 was formed by | 5
CIDOC CRM | P20 had specific purpose | 4
CIDOC CRM | P50 has current keeper | 4
CIDOC CRM | P53 has former or current location | 4
CIDOC CRM | P134 continued | 4
ISAD Ontology | ISAD27 has accruals | 4
CIDOC CRM | P44 has condition | 3
CIDOC CRM | P99 was dissolved by | 3
CIDOC CRM | P122 borders with | 3
DataObject | DOP1 approximate date value | 2
CIDOC CRM | P17 was motivated by | 2
CIDOC CRM | P48 has preferred identifier | 2
CIDOC CRM | P100 was death of | 2
CIDOC CRM | P121 overlaps with | 2
CIDOC CRM | P24 changed ownership through | 1
CIDOC CRM | P25 moved by | 1
CIDOC CRM | P26 moved to | 1
CIDOC CRM | P49 has former or current keeper | 1
CIDOC CRM | P54 has current peranent location | 1
CIDOC CRM | P71 is listed in | 1
CIDOC CRM | P143 joined | 1
CIDOC CRM | P144 joined with | 1
CIDOC CRM | P145 separated | 1
CIDOC CRM | P146 separated from | 1
CIDOC CRM | P151 was formed from | 1
CIDOC CRM | P173 ends with or after the start of | 1
CIDOC CRM | P183 starts after the end of | 1

As expected, the CIDOC CRM classes and properties are prevalent in Table 4 and
Table 5, indicating that CIDOC CRM is ArchOnto’s base ontology.

Among the classes used, some stand out, being used more intensively,
noticeably the E41 Appellation, DOE8 String, and E52 Time-Span. E41
Appellation is a unifying object for the names of different entities, which
justifies its frequent use. The DOE8 String class is also widely used because
it is used to insert and verify textual elements, such as titles, identifiers,
and names (such as the names of places, activities, groups). In the extensions
of CIDOC CRM for archives, the classes for Titles (ARE3 Supplied Title), Role
Type (ARE8 Role Type), and Documentary Typology (ARE11 Documentary Typology)
also appear repeatedly.

Regarding properties, we have high numbers for properties such as DOP7 string
value, used to express the string values, P1 is identified by, associating
objects with multiple identifiers, and P2 has type, used for associating
individuals with their types. In the extensions to CIDOC CRM, ARP12 has level
of description is used for all 25 records as expected, and to represent the
level of description of documents related to the 25 records in the sample.
Properties from the ISAD Ontology are used to represent information that comes
from textual fields. Properties from the Data Object ontology are also
extensively used, dealing with literal values.

From 2652 properties used to represent the 25 records, 1498 are from CIDOC
CRM, 828 from DataObject, 176 from ISAD Ontology, 80 from ArchOnto, and 70
from N-ary. With this, we can observe the importance and multidisciplinarity
that CIDOC CRM presents and how the ontologies created to represent the
archival documents complement it.

##  5\. Rules for the Automatic Migration of ISAD(G) records to ArchOnto

Based on the experience of manually representing the 25-records sample, and
envisioning the automatic migration of the existing records to ArchOnto, we
defined rules to map each ISAD(G) element. These rules are presented in Table
6 using the Mapping Description Language (Bountouri and Gergatsoulis, 2011).

Table 6. From ISAD(G) to ArchOnto: migration rules Rule No. | ISAD(G) | ArchOnto Path
---|---|---
1 | ISAD{D1} |  E31 Document{=D1};
|  |  $D1 -> P128 is carried by -> E22 Human-Made Object{=HMO1};
|  |  $D1-> P67 refers to -> E33 Linguistic Object{=LO1};
2 | $D1-¿Description Level{DL} | $D1 -> ARP12 has level of description -> ARE1 Level of
|  |  Description{=DL};
3 | $D1-¿Reference Code{RC} | $D1 -> P1 is identified by -> E42 Identifier {=RC} ->
|  |  P2 has type -> ARE5 Identifier Type {=’Reference Code’};
4 | $D1-¿Title{T} |  $D1 -> P102 has title -> E35 Title -> DOP7 stringValue -> T;
5 | $D1-¿Formal Title{FT} | $D1 -> P102 has title -> ARE2 Formal Title -> DOP7 stringValue
|  |  -> FT;
6 | $D1-¿Supplied Title{ST} | $D1 -> P102 has title -> ARE3 Supplied Title -> DOP7 stringValue
|  |  -> ST;
7 | $D1-¿Production Date{SD, ED} | $HMO1 -> P108 was produced by -> E12 Production ->
|  | P4 has time-span -> E52 Time-Span -> P1 is identified by ->
|  |  E41 Appellation -> L2DO hasValue -> DOE11 Interval {=INT1};
|  |  $INT1 -> DOP6 startDateValue -> SD;
|  |  $INT1 -> DOP2 endDateValue -> ED;
8 | $D1-¿Production Date{PD} | $HMO1 -> P108 was produced by -> E12 Production ->
|  | P4 has time-span -> E52 Time-Span -> P1 is identified by ->
|  | E41 Appellation -> L2DO hasValue -> DOE10 Instant ->
|  |  DOP8 timestamp -> PD;
9 | $D1-¿Dimension{DIM} |  $HMO1 -> P43 has dimension -> E54 Dimension {=DIM1};
|  |  $DIM1 -> P91 has unit -> E58 Measurement Unit;
|  |  $DIM1 -> P90 has value -> DIM;
10 | $D1-¿Extension{EXT} |  $HMO1 -> P43 has dimension -> ARE4 Extension{=E1};
|  |  $E1 -> P91 has unit -> E58 Measurement Unit;
|  |  $E1 -> P90 has value -> EXT;
11 | $D1-¿Support{SP} |  $HMO1 -> P45 consists of -> E57 Material{=SP};
12 | $D1-¿Language{LG} |  $LO1 -> P72 has language -> E56 Language{=LG};
13 | $D1-¿Physical Location{PL} | $D1 -> P1 is identified by -> E42 Identifier {=PL} ->
|  |  P2 has type -> ARE5 Identifier Type {=’Physical Location’};
14 | $D1-¿Original Numbering{ON} | $D1 -> P1 is identified by -> E42 Identifier {=ON} ->
|  |  P2 has type -> ARE5 Identifier Type {=’Original Numbering’};
15 | $D1-¿Previous Location{PreL} | $D1 -> P1 is identified by -> E42 Identifier {=PreL} ->
|  |  P2 has type -> ARE5 Identifier Type {=’Previous Location’};
16 | $D1-¿Creation Date{CD} | $LO1 -> P94 was created by -> E65 Creation -> P4 has time-span
|  | -> E52 Time-Span -> P1 is identified by -> E41 Appellation ->
|  |  L2DO hasValue -> DOE10 Instant {=INST1};
|  |  $INST1 -> DOP8 timestamp -> CD;
|  |  $INST1 -> P2 has type -> ARE6 Date Type {=’Creation Date’};
17 | $D1-¿Parent Record{PR} |  $D1 -> P165 incorporates -> $PR;
Conjugation of rules is done with ´;´. V outputs the value of the variable V;
$V is the element identified by the value of the variable V;
and {=V} is the assignment of the value of V. In the assignment, if V is not
yet defined, it takes the value of ‘V’. The assignment of a
literal is done with =‘literal value’.

The migration rules are composed of two parts. The first part represents the
ISAD(G) representation, and the second represents the ArchOnto Path. To read
the rules, it is essential to consider that, in the ArchOnto Path, classes and
properties of the ontology are used, as well as symbols that represent what
was already present in ISAD(G) – represented by “{}” in the first part of the
rule, as can be seen, for example, in {=D1}.

To create a document, we can use the first rule, which is applied for each
ISAD(G) record associated with a physical part and a conceptual part. The
physical part describes aspects of the physical object, such as dimension and
support. It is important to emphasize that, in digital objects, the physical
object is not palpable. The conceptual part, on the other hand, includes
aspects such as the language in which the document is written. The path
declares that a document (E31 Document) is carried by (P128 is carried by) a
Human-Made Object (E22 Human-Made Object), and the same document refers to
(P67 refers to) a Linguistic Object (E33 Linguistic Object).

To represent the title of a document, we can use rules 4, 5, and 6, depending
on the type of title available on the document. When a document has a formal
title type, Rule 5 must be taken into account. If the document has a title
with the type supplied, Rule 6 must be used. If the type of title is not
present in the document, Rule 4 should be used. These three rules follow
similar patterns since each title is always associated with a document (E31
Document), through the property P102 has title, regardless of its type. The
following path shows how to represent document with a Formal Title (ARE2
Formal Title). A document ($D1) has a formal title (P102 has title -¿ ARE2
Formal Title) which is represented by a string (DOP7 stringValue).

To represent the date of creation of a record, rule 16, we need to define two
different instants. The first one corresponds to the creation of the
description, and the second to the more recent modification. The path
describes a Linguistic Object ($LO1) created by the event of creation (P94 was
created by -¿ E65 Creation), which has two time-spans (P4 has time-span -¿ E52
Time-Span) identified by an appellation with an instant (P1 is identified by
-¿ E41 Appellation -¿ L2DO hasValue -¿ DOE11 Instant). This instant has a
timestamp (DOP8 timestamp) and a date type, depending on if it is the Creation
Date or the Last Modification of the record (P2 has type -¿ ARE6 Date Type
{=’Creation Date’} or {=’Last Modification’}).

In addition to the rules presented in the table, there are also rules for the
use of the ISAD Ontology. All properties of the ISAD Ontology are used in the
same way, and all properties have the E31 Document class as domain and the
xsd:string as range. For example, E31 Document -¿ ISAD1 has title -¿
xsd:string.

##  6\. Discussion of Results

The CIDOC CRM is a model designed for museums and it explored to represent the
main concepts for other cultural heritage domains. This work is centered on
the development of ArchOnto, an ontology to support a new archival information
system at the Portuguese National Archives. The ontology is based on the CIDOC
CRM for the core concepts, includes extensions to deal with archival-specific
elements, and incorporates some additional ontologies to ease the transition
from legacy records and deal with practical aspects of the validation of
literal values. The CIDOC CRM can take care of the representation for most of
the information in the archival model but was not suitable to represent all
the major elements in the ISAD(G) standard. This led to the creation of
additional classes and properties, some of them organised as sub-ontologies to
complete the model.

Although the model is designed to support a new workflow for archival
description, the existing records constitute a huge resource with valuable
information generated by specialists. This work explores the representation of
existing records, from the legacy DigitArq database, using the ArchOnto
ontology. It is visible that CIDOC CRM contributes with most of the core
concepts, but also that extensions are required to deal with archival records.

Working with information from existing records it was possible to conclude,
for instance, that the E55 Type class is extensively used, due to the wide
range of concepts it supports. The examples made it clear that a flat use of
E55 Type would provide only very general information on the category of object
that it would classify, limiting the use of “type” as an effective means for
enforcing controlled vocabularies. One of the extensions in ArchOnto was
therefore a set of subclasses of E55 Type to specialize types that are common
in archives, such as those for level of description, dates, or document types,
most of them corresponding to controlled vocabularies in the domain of
archives. So far, a list of 15 subclasses has been considered relevant by the
archive specialists.

Table 7. Status of the migration of ISAD elements Element | Representation in ArchOnto
---|---
Identity Statement Area |
1.1. Reference code (mandatory) | C
1.2. Title (mandatory) | C
1.3. Dates (mandatory) | C
1.4. Level of description (mandatory) | C
1.5. Extent and medium of the UoD (mandatory) | C
Context Area |
2.1. Name of Creator (mandatory) | C
2.2. Administrative/biographical history | PC
2.3. Archival history | PC
2.4. Immediate source of acquisition or transfer | PC
Content and Structure Area |
3.1. Scope and content | PC
3.2. Appraisal, destruction and scheduling information | PC
3.3. Accruals | NS
3.4. System of Arrangement | NS
Conditions of Access and Use Area |
4.1. Conditions governing access | NS
4.2. Conditions governing reproduction | NS
4.3. Language/scripts of material | C
4.4. Physical characteristics and technical requirements | C
4.5. Finding aids | NS
Allied Materials Area |
5.1. Existence and location of originals | C
5.2. Existence and location of copies | C
5.3. Related units of description | PC
5.4. Publication note | PC
Notes Area |
6.1. Note | PC
Description control area |
7.1. Archivist’s Note | PC
7.2. Rules or conventions | NS
7.3. Date of description | C
C, PC, and NS stand for Complete, Partially Complete, and Not Started,
respectively.

On the other hand, the examples have led us to observe that the most
descriptive elements, such as “Scope and content” and “Administrative/
Biographical history”, include information on e.g. events, people,
organizations, entities, that the archive specialists consider important
enough to be captured in a structured manner, such as allowed by the CIDOC
CRM. Therefore, the representation of these elements in ArchOnto is not
processed as a direct mapping. Still, the identification of relevant entities
that are common in the textual information of these elements has already
started. Relevant concepts are those of person and group (that can be
represented with classes E21 Person and E74 Group, respectively), event (E5
Event), date (E54 Time-Span), and place (E54 Place). These are clearly central
concepts in CIDOC CRM as well. For the migration of the textual elements that
can provide such entities, we will use natural language processing tools to
analyze the content and extract the concepts. The inference of ontological
relations will also be considered.

It is interesting to assess the extent to which the ISAD(G) elements in
existing records have been mapped to ArchOnto. Table 7 list the elements,
grouped by their area in ISAD(G) and shows the status of their representation
in the manual representation using ArchOnto. “C” stands for “Complete”, “PC”
for “Partially Complete” and “NS” for “Not Started”. For elements marked as
not started, although they are not yet directly represented, the CIDOC CRM
concepts to represent the information present in the ISAD(G) description are
already identified.

When analyzing existing records in DigitArq, it was possible to observe many
null or blank values in ISAD(G) elements. Further analysis led to the
conclusion that this is a result of two of the principles adopted in ISAD(G):
description proceeds from general to more specific, and there should be no
repetition of information (International Council on Archives, 2000). An
element filled at fonds level, for instance, is not repeated for a series that
is part of the fonds – but it may be overridden by more specific information.
As the standard has a hierarchical structure, it is only mandatory to fill
some of the elements at the top level. With this, a selected record inherits
the description corresponding to the level immediately above, in case a new
value is not provided in its own record. As the systematic migration becomes
complete, inferences will be performed by the applications that explore the
knowledge graph. For missing values in ISAD(G) elements, the corresponding
records up the hierarchy should be considered.

##  7\. Conclusions

This work is part of a broader endeavour that started with a new vision for
the Portuguese Archives, one where the information in the archives, which is
increasingly requested by citizens for a diversity of purposes, is explored in
its connections to the wider information world. This plan requires a vast
investment in conceptualization, modelling, prototyping, user testing,
development and evaluation.

This work reports on the activities related to the definition of a linked open
data model for archives. It started with a study of the CIDOC CRM standard by
the archival specialists. This provided insight into the level of detail at
which current models were exploring the representation of cultural assets. On
the other hand, the computer science team had previous work based on ISAD(G)
and were familiar with the Digitarq system used by the Portuguese archives.
Their path included a thorough study of CIDOC CRM and a systematic analysis of
the contents of existing records.

This starting point allowed the continuation of work in three parallel lines:
the definition of the data model, the selection of a technology stack to
support the knowledge graph, and the definition of user profiles and
interfaces for user access and interaction. These tasks are reaching their
conclusion, giving way to those that rely on their results.

Building on the data model, an automatic migration process is ongoing. Rules
are already in place for most of the ISAD(G) elements for which the mapping
into ArchOnto is straightforward. Extra effort is required for elements that
are rich in textual content an will require more elaborate natural language
processing for extraction.

Building on the selected technology stack, a triple store is being built to
incorporate the results of the migration and to support the prototype
applications that include generic search interfaces and environments for
archival activities such as collection organisation, description and
conservation.

Moreover, the overall plan also includes two additional aspects: text
extraction from digital documents and knowledge propagation. The former
accounts for the exploration of the textual content of the born-digital
documents. The goal is to ease their description by generating automated
elements of description to be validated and completed by the archivists. The
latter proceeds to connect the information in the archives to other sources,
providing archival users with a glimpse of the relations between entities in
the archives and their counterparts in more informal data sources.

One aspect that is very relevant in this plan is the conformity to the
standards and recommendations by the archival professional bodies, namely the
International Council on Archives (ICA). ICA is developing a linked data model
(RiC-CM). By the time our project started, in January 2019, little information
was available about this new model. At that time, we started to explore CIDOC
CRM, a model originated in museums, with a long period of development that
makes it a stable model. The study of RiC-CM and its connections to CIDOC CRM
are in the scope of future work related to this project. After all, an
overarching goal for cultural heritage platforms is to link objects from
different sources. Regardless of what actual model you build a specific system
on, they are expected to interoperate and be equipped with pathways for
communication that promote seamless perusal of cultural heritage assets across
institutions and technologies.

###### Acknowledgements.

This work is financed by National Funds through the Portuguese funding agency,
FCT – Fundação para a Ciência e a Tecnologia within project
DSAIPA/DS/0023/2018. Inês Koch is also financed by National Funds through the
Portuguese funding agency, FCT – Fundação para a Ciência e a Tecnologia within
the research grant 2020.08755.BD.

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##  Appendix A THE CLASS HIERARCHY WITHIN ARCHONTO’S ONTOLOGIES

Table 8. The class hierarchy within ArchOnto’s ontologies Ontology | Classes
---|---
CIDOC CRM | E35 Title
Archonto | — ARE2 Formal Title
Archonto | — ARE3 Supplied Title
CIDOC CRM | E39 Actor
Archonto | — ARE12 Organisation
CIDOC CRM | E54 Dimension
Archonto | — ARE4 Extension
CIDOC CRM | E55 Type
Archonto | — ARE1 Level of Description
Archonto | — ARE5 Identifier Type
Archonto | — ARE6 Date Type
Archonto | — ARE7 Name Type
Archonto | — ARE8 Role Type
Archonto | — ARE9 Date Certainty
Archonto | — ARE11 Documentary Typology
Archonto | — ARE13 Subject Type
Archonto | — ARE14 Place Type
Archonto | — ARE15 Acquisition Type
Archonto | — ARE16 Event Type
DataObject | DOE1 DataObject
DataObject | — DOE2 AuthorityFile
DataObject | — DOE3 Boolean
DataObject | — DOE4 Date
DataObject | — — DOE9 Approximate
DataObject | — — DOE10 Instant
DataObject | — — DOE11 Interval
DataObject | — DOE5 Decimal
DataObject | — DOE6 GeospatialCoordinates
DataObject | — — DOE12 Latitude
DataObject | — — DOE13 Longitude
DataObject | — — DOE14 Polygon
DataObject | — DOE7 Integer
DataObject | — DOE 8String
DataObject | — — DOE15 AuthorityString
DataObject | — — — DOE17 PersonName
DataObject | — — DOE16 RegexString
N-ary | PC0 CRM Property
N-ary | — PC14 Carried Out By

##  Appendix B THE PROPERTY HIERARCHY WITHIN ARCHONTO’S ONTOLOGIES

Table 9. The property hierarchy within ArchOnto’s ontologies Ontology | Property | Domain | Range
---|---|---|---
ArchOnto | ARP8 upper level | ARE1 Level of Description | ARE1 Level of Description
ArchOnto | ARP9 lower level | ARE1 Level of Description | ARE1 Level of Description
Link2DataObject | L2DO hasValue | E1 CRM Property | DOE1 DataObject
N-ary | P01 has domain | PC0 CRM Property | E1 CRM Entity
N-ary | P02 has range | PC0 CRM Property | E1 CRM Entity
DataObject | DOP1 approximateDateValue | DOE9 Approximate | xsd:dateTime
DataObject | DOP2 endDateValue | DOE11 Interval | xsd:dateTime
DataObject | DOP3 fileLocation | DOE15 AuthorityFile | xsd:string
DataObject | DOP4 hasRegex | DOE16 RegexString | xsd:string
DataObject | DOP5 name | DOE17 PersonName | xsd:string
DataObject | DOP6 startDateValue | DOE11 Interval | xsd:dateTime
DataObject | DOP7 stringValue | DOE8 String | xsd:string
DataObject | DOP8 timestamp | DOE10 Instant | xsd:dateTime
CIDOC CRM | P2 has type | E1 CRM Entity | E55 Type
ArchOnto | — ARP12 has level of description | E31 Document | ARE1 Level of Description
CIDOC CRM | P3 has note | E1 CRM Entity | ———
ISAD Ontology | — ISAD1 has title | E31 Document | xsd:string
ISAD Ontology | — ISAD2 has level of description | E31 Document | xsd:string
ISAD Ontology | — ISAD3 has reference code | E31 Document | xsd:string
ISAD Ontology | — ISAD4 has type of title | E31 Document | xsd:string
ISAD Ontology | — ISAD5 has date | E31 Document | xsd:string
ISAD Ontology | — ISAD6 has dimension and support | E31 Document | xsd:string
ISAD Ontology | — ISAD7 has administrative history | E31 Document | xsd:string
ISAD Ontology | — ISAD8 has archival history | E31 Document | xsd:string
ISAD Ontology | — ISAD9 has scope | E31 Document | xsd:string
ISAD Ontology | — ISAD10 has access condition | E31 Document | xsd:string
ISAD Ontology | — ISAD11 has current quota | E31 Document | xsd:string
ISAD Ontology | — ISAD12 has old quota | E31 Document | xsd:string
ISAD Ontology | — ISAD13 has original quota | E31 Document | xsd:string
ISAD Ontology | — ISAD14 has language | E31 Document | xsd:string
ISAD Ontology | — ISAD15 has related unit of description | E31 Document | xsd:string
ISAD Ontology | — ISAD16 has existence and location of copies | E31 Document | xsd:string
ISAD Ontology | — ISAD17 has publication notes | E31 Document | xsd:string
ISAD Ontology | — ISAD18 has notes | E31 Document | xsd:string
ISAD Ontology | — ISAD19 has system of arrangement | E31 Document | xsd:string
ISAD Ontology | — ISAD20 has physical characteristics | E31 Document | xsd:string
ISAD Ontology | — ISAD21 has description date | E31 Document | xsd:string
ISAD Ontology | — ISAD22 has last modification | E31 Document | xsd:string
ISAD Ontology | — ISAD23 has predominant date | E31 Document | xsd:string