CRMgeo: A spatiotemporal extension of CIDOC-CRM
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CRMgeo is a formal ontology intended to be used as a global schema for integrating spatiotemporal properties of temporal entities and persistent items. Its primary purpose is to provide a schema consistent with the CIDOC CRM to integrate geoinformation using the conceptualizations, formal definitions, encoding standards and topological relations defined by the Open Geospatial Consortium in GeoSPARQL. To build the ontology, the same ontology engineering methodology was used as in the CIDOC CRM. CRMgeo first introduced the concept of Spacetime volume that was subsequently included in the CIDOC CRM and provides a differentiation between phenomenal and declarative Spacetime volume, Place and Time-Span. Phenomenal classes derive their identity from real world phenomena like events or things and declarative classes derive their identity from human declarations like dates or coordinates. This differentiation is an essential conceptual background to link CIDOC CRM to the classes, topological relations and encodings provided by Geo-SPARQL and thus allowing spatiotemporal analysis offered by geoinformation systems based on the semantic distinctions of the CIDOC CRM. CRMgeo introduces the classes and relations necessary to model the spatiotemporal properties of real world phenomena and their topological and semantic relations to spatiotemporal information about these phenomena that was derived from historic sources, maps, observations or measurements. It is able to model the full chain of approximating and finding again a phenomenal place, like the actual site of a ship wreck, by a declarative place, like a mark on a sea chart.
KeywordsOntology Semantics Spatiotemporal Geoinformation CIDOC CRM GeoSPARQL
CRMgeo  defines a formal ontology intended as a global schema for integrating spatiotemporal properties of temporal entities and persistent items. Its primary purpose is to give an adequate account of the relationship of physical things and processes to spacetime, compatible with physics, besides others by explicitly introducing the differentiation of places in the real world (phenomenal) and in the world described by information (declarative), and thus integrate geoinformation available in GIS formats under a CIDOC CRM  compatible form without loss of information. More generally, it aims at integrating topological information with other types of factual knowledge in a common knowledge representation formalism suited for semantic Web technologies. To do so it links the CIDOC CRM to the OGC standard of GeoSPARQL  , making use of the conceptualisations and formal definitions that have been developed in the Geoinformation community. CRMgeo uses and extends the CIDOC CRM (ISO21127), a general ontology of human activity, things and events taking place in spacetime. It uses the same encoding-neutral formalism of knowledge representation (“data model” in the sense of computer science) as the CIDOC CRM. It can thus be implemented in RDFS, OWL, on RDBMS, as well as in other types of encoding. The background for the development of this model lies in a growing interest in enriching cultural heritage data with precise and well identifiable descriptions of location and geometry of sites of historical events or remains, objects and natural features. On the one side, there is already a tradition of more than two decades of using GIS systems for representing cultural-historical and archaeological data and reasoning on properties of spatial distribution, vicinity, accessibility and others. These systems tended to be closed and focusing more on representing feature categories by visual symbols at different scales than integrating rich contextual object descriptions. Such systems have been being extremely successful in all kinds of “geosciences”, resource management and public administration, whereas cultural heritage is a rather marginal application area. On the other hand, archives, libraries and museums keep detailed historical records with very poor spatial determination. Often the language of the source or the local context is used. At the time of creation the meaning of such expressions could have been pretty determined, but they frequently refer to wider geopolitical units only, such as “Parthenon in Athens”. They often focus on typologies, individual objects, parts and wholes, provenance, kinds of events, participating people and influential factors, rather than precise dates and periods. This practice creates problems when current users want to integrate city plans, tourism guides, detailed excavation or restoration records. The fact that “people know quite well where the Parthenon lies” or “you’ll see it when you go to Athens” is not helpful for today’s IT systems. The two traditions, the “GIS community” and the “cultural heritage community”, have developed standards which precisely reflect the two different foci—the OGC/ISO Standards for Geographic Information which are the building blocks of the GeoSPARQL ontology and the ontology of the CIDOC CRM which is the ISO standard for representing cultural heritage information. In an attempt to combine these two standards, we experienced a surprise: there is no match at any intermediate concept between the standards, notwithstanding that the CRM was explicitly intended to interface with Open Geospatial Consortium (OGC) Standards, and that neither standard allow for expressing objectively the location of something in a way robust against changes of spatial scale and time. For instance, the CRM allows for specifying a property “P\(\ldots \) has former or current location”, without declaring if the location is or was the extent of the object, was within the extent of the object or included its extent, and at which time the location was had. Before GeoSPARQL, OGC Standards and traditional Geoinformation Systems, on the other side, allowed for assigning one (or in rare cases more) precise “geometries” to a “feature”, but did not say how the real matter of the thing with its smaller irregularities relates to them. It could be a point in the feature, a circle around it, or a centimetre-precise smoothed surface. For any “feature” there is a spatial scale at which a “geometry” of a detail cannot be compared to the geometry of the whole, and the temporal validity range is not explicitly stated even if OGC Standards provide mechanisms for doing that. What is needed is an “articulation” (linkage) of the two ontologies, i.e., a more detailed model of the overlap between the two, a model allowing for covering the underdetermined concepts and properties of both ontologies. This should be done by shared specialisations rather than by generalisations. So we took a step back and developed a model based on an analysis of the epistemological processes of defining, using and determining places. This includes an analysis of how a question such as “Is this the place of the Varus Battle?” or “Is this the place where Lord Nelson died?”, can be verified or falsified in practice, also based on geometric specifications. This required identifying various sources of factual errors as well as incorrect data appearing in such verification processes, and also questioning the truth of the very historical record. Consequently, we reached at a surprisingly detailed model which seems to give a complete account of all practical components necessary to verify such questions, in agreement with the laws of physics, the practice of geometric measurement, and archaeological reasoning. This model appears to have the capability not only to link both ontologies but also to show the way towards correct reconciliation of data at any scale and time—not by inventing precision or truth that cannot be acquired, but by quantifying or delimiting the immanent indeterminacies, which is good practice in the natural sciences.
2 Model history
3 Core concepts of CIDOC CRM 6.2 to represent spatiotemporal properties of Periods (E4) and Physical Things (E18)
4 Spatiotemporal refinement in CRMgeo: differentiating between phenomenal and declarative spacetime volume, place and time span
The CRMgeo ontology explicitly introduces the differentiation of “phenomenal” and “declarative” extents in space, time or spacetime in the real world (phenomenal) and the world described by information (declarative). In the real world, exact spatiotemporal properties of phenomena [Periods (E4) or Physical Things (E18)] can not be known due to factors such as fuzzy boundaries of the phenomena and errors in measurements. Nevertheless, the spatiotemporal properties exist and CRMgeo introduces them as Phenomenal Spacetime volume (SP1), Phenomenal Place (SP2) and Phenomenal Time Span (SP13) as subclasses of Spacetime volume (E92), Place (E53) and Time Span (E52). They derive their identity from a phenomenon that has occupied or still occupies a unique Spacetime volume (E92).
5 GeoSPARQL overview
Core component: defines top-level RDFS/OWL classes for spatial objects
Geometry component: defines RDFS data types for serialising geometry data, RDFS/OWL classes for geometry object types, geometry-related RDF properties, and non-topological spatial query functions for geometry objects
Geometry topology component: defines topological query functions
Topological vocabulary component: defines RDF properties for asserting topological relations between spatial objects
6 Linking CIDOC CRM and CRMgeo concepts to GeoSPARQL
The model of CRMgeo 1.2 incorporates the changes realised in CIDOC CRM 6.2. Making the Spacetime volume (E92), which is intended a Phenomenal Spacetime volume (SP1), a super class of Period (E4) and Physical Thing (E18) enables us to define geosparql:Feature as a superclass of Phenomenal Spacetime volume (SP1). Period (E4) and Physical Thing (E18) will then inherit the properties of geosparql:Feature, in particular the elaborated topology relations that can be applied between geosparql:Spatial Objects, the superclass of geosparql:Feature and geosparql:Geometry. The introduction of a new class Geometry (SP15) in CRMgeo 1.2 allows for an easier implementation as it comprises the union of geometric definitions and the declarative places that these geometries define. The new relationships at class level between CRMgeo 1.2 and Geo-SPARQL are illustrated in Fig. 5.
7 Example of approximating the Redoubtable wreck
Making the Spacetime volume (E92) in CIDOC CRM a superclass of Period (E4) and Physical Thing (E18) introduces an integrated view of space and time into the CRM that allows for spatiotemporal modelling and reasoning based on semantic relations between CRM instances. Before the introduction of the Spacetime volume there was either temporal or spatial reasoning but the inherent relation between the two could not be modelled. The differentiation between phenomenal and declarative Spacetime volume, Place and Time Span in CRMgeo defines identity criteria for real world spatiotemporal properties of Periods and Physical Things and spatiotemporal properties created from information sources like historical documents, maps, observations or measurements. This differentiation allows for a modelling and reasoning of the relations between real world locations and temporal extents of things and events and the available information about their locations and temporal extents. This is of particular interest when trying to determine the actual location of a thing, based on several information sources like nautical charts and logbooks from different nations that use different reference systems, scales and units. The linking of CRMgeo to GeoSPARQL allows for a representation of coordinate information compliant with OGC standards and the application of the elaborated topological relations GeoSPARQL defines. As a result the concepts of CRMgeo enable information integration on a spatiotemporal level based on the semantics defined in CIDOC CRM and making use of the technologies and definitions based on OGC standards.
Open access funding provided by University of Innsbruck and Medical University of Innsbruck.
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