The CIDOC CRM provides roughly 86 classes and 137 relationships along with scope notes describing their intended meaning and application. In this section, only selected classes and properties will be introduced in order to provide a general understanding of the workings of the CRM and its influence on the interpretative analysis of the inquiries. Entities incorporated in the general patterns will be introduced or further discussed in the chapter “Results” (V).
Persistent and Temporary Things The classE1 CRM Entityrepresents all things in the domain of discourse of the CRM (Crofts et al.,2006, 2). Nearly all 86 classes of the CRM are direct or indirect sub-classes of the classE1 CRM Entity.46 The principal top-level entities of the CRM are shown in Figure4. All other classes of the CRM can be understood as being specializations of one of these entities (Oldman,2014, 8).
Figure 4– The top-level classes of the CRM, taken from Doerr (2003, 85).
All these specializations are essentially split up into two principal trees of classes: persistent and temporal entities which primarily differ in terms of their behaviour in time. Persistent entities, represented by the classE77 Persistent Item, are things which endure over time (Crofts
46The only exception is the classE59 Primitive Value.
et al.,2006, 34). According to Masolo et al., in philosophy, they are also calledendurantsor continuants. Their identity persists over an indeterminate period of time even if their physical existence ends; for example, physical objects such as the Titanic or the World Trade Center, particular persons such as Albert Einstein or Ramesses II, or even ideas (Masolo et al.,2003, 10-11). This holds for anything which humans can remember. In other words, persistence means that their existence has the potential to span multiple, successive events with the same identity in which they can “participate”.
Temporal entities, on the other hand, represented by the classE2 Temporal Entity, are phenom-ena which occur only during a limited time frame (Crofts et al.,2006, 2). They exhibit temporal parts as time proceeds and their entirety is spread out over time. Their substance is the change, or even phases without change, implying change before and after. In language they correspond to the verbs or gerunds. According to Masolo et al., in philosophy they are also calledperdurants oroccurrents. Their existence is bound in time and ends after the fact, for example, natural events and activities of people (Masolo et al.,2003, 10-11). In other words, persistent items
“can be repeatedly recognized within the duration of their existence by criteria” while temporal entities can only do so “by continuity or observation” (Crofts et al.,2006, 30).47
The interaction of instances from both trees of classes denominates a fundamental modelling decision of the CRM. Persistent entities such as people or things may either actively or passively participate in the occurrence of temporal entities; they may be affected by their occurrence, or witness it. Figure4also illustrates the pivotal role of temporal entities as a kind of hub connecting the others, such as actors, things, places, and time. Thisevent-basedapproach is fundamental to the methodology of the CRM.
Events and Activities (Temporal Entities) One of the most important design principles of the CRM is to represent the past as a series of discrete events. Material and immaterial persistent entities are present at events either as concepts or via physical information carriers such as books or paintings. An object, more precisely objects made by man, only exists if some event has happened previously with this man-made object as its result or product. Natural things may exist as results of processes which cannot be cut into a discrete genesis; in other words, everything that has happened to an object – its administration, scholarly research, things that have happened to it in the past – as a part of events which have expressed part of a story. We can thus understand lives from the context of the relationships between things and where they might have encountered one another.
History, therefore, is conceptualized in the CRM as meetings of persistent entities through events in time and space (Doerr and Iorizzo,2008, 7-8). As already discussed, the CRM also uses events in order to further reduce the number of relationships by grouping other entities around the notions of events. This view is empirically supported as many existing metadata
47The philosophical discussion of the distinction is confusing, even though it is intuitively very clear. The German philosophical termsSeiendes(persistent entities) andWerdendes(temporal entities) are more precise.
schemas indeed directly or indirectly support such event-based perspectives and representations of history (Doerr and Iorizzo,2008, 8).48
Figure 5– The event-centric approach of the CRM, taken from Doerr (2003, 87).
Figure5shows an example of an event-centric description; that is, the meeting of Pope Leo I and Attila the Hun. The CRM indirectly connects the two particular persons, “Pope Leo I” and
“Attila the Hun”, via the particular event with a mediating function, “Attila Meets Leo I”. The persons are said to have performed this event and must, therefore, have met each other. Even though there is no direct relationship between the two persons we can assert that they must have met each other at some place at some point in time.
The example also represents the birth and death events of both actors and thereby exemplifies the historical and temporal perspective of the CRM. As Lin et al. state, human thinking tends to compress complex paths of relationships into more simple ones while being aware of the whole context, a phenomenon also analyzed by Fauconnier and Turner (2003). In the CRM, these compressions are normalized by its event-based approach towards their implicit constituents.
The concept of “mother” is an example where human thinking by-passes the occurrence of the
“birth event”, while the CRM explicitly asserts the “birth event” in its wider context (Lin et al., 2008, 117).
48See, for example, mappings of the TEI to the CRM in Ore and Eide (2009).
Not only does the CRM unpack such compressions; the interpretative analysis of the inquiries identify implicit yet pivotal constituents – either in terms of classes or relationships – and renders them explicit by representing them in the ontological model. For this purpose, either existing entities of the CRM are evaluated and reused, or, where necessary, new ones are introduced by defining new classes or properties as organic extensions of the CRM. This process of formalizing and explicating implicit ontological entities during the interpretative analysis will be necessarily determined by the event-based approach, which therefore is one of the crucial epistemological influences derived from the CRM while analyzing the inquiries, as will be further discussed later on (IV:3.2).
The concept of aperiod(Doerr et al.,2010a), represented by the classE4 Period(Crofts et al., 2006, 3-4), is one of the most general temporal entities in the CRM. The two other relevant high-level temporal entities areE5 Event, and its sub-classE7 Activity. The classE5 Event comprises phenomena which result in recognizable “changes of states in cultural, social or physical systems” and have ramifications onendurants(IV:3.1), physical entities such as persons or things, or conceptual entities such as “ideas, concepts, products of the imagination or common names” (Crofts et al.,2006, 4). Instances of the classE5 Eventare not purposefully caused by actors but by a force majeure, such as natural disasters, accidents, or celestial phenomena.
In comparison to instances ofE7 Activity, instances of the classE5 Eventcan be interpreted as “unintentional events” or “non-activities” which means they happen with or without the intentional participation or immediate causation of humans. To be sure, the classE5 Eventis a generalization of the classE7 Activitywhich means that events neither require an activity nor exclude such. In other words, every activity is also an event but not every event is also an activity.
The classE7 Activitythen comprises any kinds of acts which have been carried outintentionally by individual people or groups (Crofts et al.,2006, 5-6). The meeting of Pope Leo I. and Attila the Hun is such an example of an instance ofE7 Activity. Such deliberate and intentional actions are conceptualized as activities. It is not important whether the activity actually happened but only if there is a potential for deliberate and intentional action, and, of course, is deemed relevant knowledge from the point of view of documentation.
Through these temporal entities – and their numerous sub-classes, some of which will be introduced in the following paragraphs – persistent entities such as actors and things interact and are generally connected in time and space.
Actors and Things (Persistent Entities) Actors and things are both persistent entities and may be actively or passively present at events and activities during which they meet and interact.
The classE39 Actor comprises people either as individuals or as groups, who “have the potential to perform intentional actions for which they can be held responsible” (Crofts et al., 2006, 19). One of its two sub-classes isE21 Personwhich represents individual people who have lived or are assumed to have lived such as Karl Marx or Saint Paul (Crofts et al.,2006, 12). The other sub-class isE74 Groupwhich represents groups of people, which means any gatherings
or organizations of more than two persons. Examples of groups include political parties such as the Communist Party of Germany (KPD), or the National Socialist German Workers’ Party (NSDAP), or political offices such as the chancellor of the Federal Republic of Germany (FRG), or the party leader of the Greens, but also the concept of family (Crofts et al.,2006, 33).49
The ontological analysis of the inquiries focuses on deliberate and intentional actions (be-wusste Handlungen)and the identification of these deliberately and intentionally acting entities.
In this context, the classE39 Actor is also a good example of another important modelling principle applied during the analysis: when there is doubt as to whether a person or group has acted, then simply “an” actor is assumed. As already mentioned above, this allows us to deal with uncertainty in the model and the represented knowledge.
Actors then may be either actively or passively involved in events or activities. The high-level propertyP11 had participant (participated in)expresses this relationship (Crofts et al.,2006, 42).
There are several sub-properties which specify the particular relationship between actor and event.
Other persistent entities such as physical things as well as conceptual objects such as ideas, concepts or products of the imagination may be present at or used in the context of an event or activity. For the purposes of this study, the two classesE73 Information ObjectandE24 Physical Man-Made Thingare the most important. Simply put, both classes and their respective sub-classes are in a relationship where a physical carrier, the physical man-made thing, such as a sheet of paper, carries some content (the information object), which in this example would be written on the sheet of paper. More formally, instances of the classE73 Information Objectare identifiable but immaterial things in the sense of any kind of textual or visual contents whose existence and identity do not depend on the material properties of one particular carrier (Crofts et al.,2006, 32-33). The same text or image may be carved in stone and painted on a board.
In other words, the classE73 Information Objectcomprises propositions in any symbolic form, such as words of a particular language, or letters and characters from an alphabet. Instances ofE24 Physical Man-Made Thingare persistent and physical things which have been purposely produced by the activity of an actor (Crofts et al.,2006, 13). For example, a report written by a student is a physical man-made thing, while the contents of that report are an information object. This principle division allows for a description of contents independently from their physical carriers; for example, a text may be carried by the original sheet of paper on which it was written, while copies of the same text may exist, for example, as a microfiche or in digital form.
The presence of physical things and conceptual objects during events is expressed by the
49Institutions or groups of people with legal recognition as a group are represented by the classE40 Legal Bodywhich is a sub-class ofE74 Group(Crofts et al.,2006, 19). Legal bodies may act collectively and be held responsible like an individual agent. This class, however, is not used in the AKM: Differentiating between E74 Group and E40 Legal Body is difficult, not least because the CRM does not specify any distinct properties for E40 Legal Body. For the ontological representation of the subject matter of the interest of the inquiries, the distinction as to whether a group or legal body has or has not acted has not been relevant.
high-level propertyP12 occurred in the presence of (was present at)(Crofts et al.,2006, 42-43).
The property also has several sub-properties specifying different notions of presence.
Apart from properties describing the relationship between persistent and temporal entities, many others exist such as part-whole relationships expressing for example the membership of actors in groups, or properties expressing a sequential succession of, for example, events.
Another fundamental example – shown in Figure5– is that of how persistent entities such as actors, physical things, and conceptual objects come into and leave, existence itself.
For actors, for example, there are the specific event classesE67 Birth(Crofts et al.,2006, 30) andE69 Death(Crofts et al.,2006, 31), during which persons come into existence, are born, and leave existence; that is, die a natural or unnatural death. Similar events pertain to the creation and destruction of physical things and conceptual objects.
The top-level propertyP92 brought into existence (was brought into existence by)(Crofts et al., 2006, 65) connects actors and things with the events via which they came into existence – mediated by the event sub-classE63 Beginning of Existence(Crofts et al.,2006, 29) – while the top-level propertyP93 took out of existence (was taken out of existence by)(Crofts et al.,2006, 65-66) connects actors and things with events of termination – mediated by the event sub-class E64 End of Existence(Crofts et al.,2006, 29). Again, these two top-level properties have several sub-properties which specify different qualities of the general relationship.
Time and Place The interaction of persistent and temporal entities occurs in time and space.
The CRM provides the necessary means to adequately represent the approximate time-span during which an event or activity occurred. The details of how time is represented in the CRM would exceed the scope of this study. An introduction to some of the difficulties of time representation in (an archaeological) context of the CRM can be found in Doerr et al. (2010b).
The AKM refers to the available documentation and modelling options provided by the CRM for describing and specifying time-spans of temporal entities.
The class E52 Time-Span“comprises abstract temporal extents, in the sense of Galilean physics, having a beginning, an end and a duration” and is used “to define the temporal extent of instances ofE4 Period,E5 Eventand any other phenomena valid for a certain time” (Crofts et al.,2006, 23-24).
Instances of time-spans are always only approximations of the actual time-spans of events because historical knowledge is necessarily imperfect. The CRM, furthermore, provides proper-ties to specify the beginning, end, and duration of a time-span, or to have a time-span fall within the duration of another. Even if a particular time-span is a vague approximation, as soon as this time-span is used for two events, they would be known to have occurred simultaneously (Crofts et al.,2006, 23-24).
Similar to time, the representation of geographical and spatial information also constitutes a complex topic in its own right. Here too, the details of modelling such information would exceed the scope of this study. Doerr and Hiebel (2013) provide a detailed discussion of related
issues. The AKM refers to the available documentation and modelling options provided by the CRM for describing and specifying geographical and spatial entities and information.
The classE53 Place“comprises extents in space, in particular on the surface of the earth, in the pure sense of physics: independent from temporal phenomena and matter” (Crofts et al.,2006, 24-25). Examples of instances ofE53 Placeare typically immobile objects such as “buildings, cities, mountains, rivers, or dedicated geodetic marks”, but also mobile objects such as ships.
Finally, any CRM entity may be named, provided with an identifier, or given type information.
Appellations and Types (Persistent Entities) The CRM fundamentally distinguishes between instances representing real-world entities, particulars, and the names and identifiers which refer to them: “The relationship between entities and the identifiers that are used to refer to the entities, and the ambiguity of reference, are part of the historical reality that is to be described rather than to be resolved in advance” (Doerr and Iorizzo,2008, 7).
The class E41 Appellation comprises “all proper names, words, phrases or codes, either meaningful or not, that are used or can be used to identify a specific instance of some class within a certain context” (Crofts et al.,2006, 20). Examples include names of actors, object identifiers, or place appellations such as addresses, or titles of documents.
In several cases, the range of a property is the classE55 Typewhich then can “refer in general to things of a certain kind” (Doerr,2003, 85) and may further characterize or classify instances of other classes. The classE55 Typecomprises “arbitrary concepts (universals) and provides a mechanism for organising them into a hierarchy” (Crofts et al.,2006, 25).
Most importantly, the “class E55 Type can be regarded as a metaclass (a class whose instances are universals), used to denote a user-defined specialization of some class or property of the Model, without introducing any additional formal properties for this specialization” (Crofts et al.,2006, 25). In the context of this study, the facility ofE55 Typeto express that an entity is of a kind; that is, that it has a type, will play an important role.
Advantages of the CRM The CRM is a core ontology for the cultural and historical domain for which other comparable ontologies and conceptual models exist, such as theSuggested Upper Merged Ontology50(SUMO) or theDescriptive Ontology for Linguistic and Cognitive Engineering51 (DOLCE). The CRM has been chosen over such ontologies for a number of reasons, most of which have been already discussed in this section.
Most importantly, the CRM is firmly grounded in an “empirical analysis of real practice and local knowledge” (Oldman,2014, 4) and therefore already provides empirical evidence regarding essential ontological entities relevant to the historical and cultural domain. Other ontologies lack such an empirical basis such as DOLCE, which is mostly based on intuition and provides a theoretically motivated logical description interpreting WordNet, an all-purpose
50http://www.adampease.org/OP/
51http://www.loa.istc.cnr.it/old/DOLCE.html
dictionary free of context.
In other words, the CRM does not prescribe what to document but “brings into a homogen-eous, integrated form what has already been documented” (Doerr et al.,2011). Since this study stresses the importance of empirically based representations of user needs, we will consider and evaluate the CRM for further use.
This empirical foundation also implies that the CRM is complementary to many metadata standards. For example, the CRM has been mapped to metadata standards such as the EAD, the most prominent encoding standard for archival aids. In the context of this study, these mappings allow for easy integration and comparison between the two ontologies. Furthermore, the CRM is aligned with other cultural heritage domain ontologies such as DOLCE orFunctional
This empirical foundation also implies that the CRM is complementary to many metadata standards. For example, the CRM has been mapped to metadata standards such as the EAD, the most prominent encoding standard for archival aids. In the context of this study, these mappings allow for easy integration and comparison between the two ontologies. Furthermore, the CRM is aligned with other cultural heritage domain ontologies such as DOLCE orFunctional