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title: "2. Architecture"
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# Architecture

ArchOnto is 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)**:** the core of ArchOnto, providing the concepts and properties to capture archival records’ essential features, e.g., event, date, location, person, group.

* **N-ary:** 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.

* **DataObject:** auxiliary ontology to deal with literal values and their validation in ArchOnto. Comprises classes and data properties for the simple types in the ontology. In this ontology, the names of classes are preceded by **DOE** (from **D**ata**O**bject **E**ntity), and the names of properties are preceded by **DOP** (from **D**ata**O**bject **P**roperty).

* **ISAD Ontology:** matches the ISAD(G) standard elements that can be directly obtained from existing records. The information is represented with Data Properties and is not atomized. 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. This ontology is only used for the existing records in DigitArq and not for newly created records based on ArchOnto.

* **Link2DataObject:** makes the connection between the CIDOC-CRM and the DataObject ontologies with a single property to make this connection — **L2DO hasValue**.

In addition to these five ontologies, **ArchOnto** has its own 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.
CIDOC-CRM. In addition to these classes, the ontology also includes three properties which 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).

*Figure 1. ArchOnto architecture*