Pre-print full text with figures. To be published in International Journal of Geomatics and Spatial Analysis

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Conceptual basis for a cultural heritage data model for INSPIRE

César Parcero-Oubiña, Pastor Fábrega-Álvarez, Juan Manuel Vicent-García, Antonio Uriarte-González, Alfonso Fraguas-Bravo, Isabel del-Bosque-González, Carlos Fernández-Freire, Esther Pérez-Asensio

1. Introduction

The concept of Cultural Heritage implies a great deal of complexity which, in the recent past, has become the subject of an increasingly intense theoretical debate regarding not only its definition but also its underlying content. Considered from a distance, and at its most generic level, most people understand Cultural Heritage as something like the ensemble of tangible and intangible achievements accumulated by a community throughout time, as long as they are recognized in the present as being relevant for them and therefore are worth being preserved for the future. However, preservation nowadays is just a small part of what heritage study and management is all about. It does still remain one of the most visible fields of practice, and is especially relevant when it comes to the interaction between heritage elements and many other fields of economic, social and political practice.

Cultural heritage is largely composed of elements with an inherent spatial dimension. In fact, the spatial component of heritage elements is most often an essential part of their characterization and even of their subjective value as cultural goods. This is equally true if we approach heritage from the perspective of experts, practitioners or enthusiasts in the field, or from the point of view of the use and management of the land and environment. But it becomes especially relevant when heritage preservation comes into conflict with the ever-growing processes of rural and urban landscape change, so characteristic of modernization, that have reached previously unknown degrees of intensity (Vicent García, 2007, 327-347).

To a great extent, an awareness of the growing weakness of heritage lies behind its legal development, from international agreements to national legislation. In the case of western democracies, the state has undertaken the duty of safeguarding cultural heritage and guaranteeing the right of citizens to access and enjoy it. Heritage has become an object of public management and administration. Therefore, the mapping of heritage elements, the knowledge of their spatial location, is the first step that needs to be taken to ensure their protection.

The enduring conflict between heritage conservation and its accessibility on the one hand, and urban and rural landscape transformation processes on the other, poses the main problem for public intervention. This concern has shaped a management practice that has begun, in most cases, by identifying and cataloging heritage features (monument catalogs, archaeological inventories, etc.) before implementing protective measures (by creating legal protection entities). This activity has engendered a network of spatial data that is quite dense, though fragmentary and heterogeneous and, all too often, barely accessible, even to the public administration itself (the Spanish case is the most familiar to us, and provides a good example of this problem, see Parcero-Oubiña, 2012, though the problem is global, see for instance Snow et al., 2006). Although this may also have been the case in many other fields, heritage management has traditionally been characterized by inefficient data management and unjustified limitations on citizens’ rights of heritage use and enjoyment (Corns and Shaw, 2010).

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As in many other fields related to spatial information, the INSPIRE directive, issued “to support Community environmental policies, and policies or activities which may have an impact on the environment”, represents both a commitment and an opportunity to integrate data and to divulge and make a diverse range of geographic information accessible to the public. Although cultural heritage is included to some extent as one of the layers considered as “reference data” (belonging to Annex I) and is also mentioned in the data specification on Buildings (Annex III), as we will see shortly, the point is not further developed within INSPIRE. However, this is a major opportunity to promote and encourage the development of cultural heritage SDIs within an interoperable framework, taking into account the spatial nature of this specific type of data in order to enhance their role within territorial governance, to help manage their protection and to bring them closer to the general public.

To aid the attainment of those objectives, several steps must be taken on different levels. On the technical level, the development of a data model and an application schema that expands the range of the already existent INSPIRE themes is what we have been considering over the last few months .

Due to space limitations, this paper will only focus on how heritage data may fit within the INSPIRE framework and the general conceptual model that we have followed to manage the spatial dimension of heritage information within that framework. The data model itself will only be outlined here, but more detailed accounts may be found elsewhere (Fernández-Freire et al., 2012, Uriarte-González et al., 2013) and an in-depth publication of the whole model is forthcoming (Fernández-Freire et al., forthcoming).

2. Cultural heritage elements in INSPIRE

As was previously stated, cultural heritage is only mentioned in passing in INSPIRE, essentially in the very specific form of protected sites. It is worth examining how INSPIRE defines the category of protected sites and, more specifically, how cultural heritage is mentioned in that definition:

“According to the International Union for the Conservation of Nature (IUCN) a Protected Site is an area of land and/or sea especially dedicated to the protection and maintenance of biological diversity, and of natural and associated cultural resources, and managed through legal or other effective means. Within the INSPIRE context, Protected Sites may be located in terrestrial, aquatic and/or marine environments, and may be under either public or private ownership. They may include localities with protection targets defined by different sectors and based on different objectives. Objectives for protection may include: the conservation of nature; the protection and maintenance of biological diversity and of natural resources and the protection of person-made objects including buildings, prehistoric and historic archaeological sites, other cultural objects, or sites with specific geological, hydrogeological or geomorphological value. Protected Sites may receive protection due to more than one type of objective, and may have a double or multifarious designation status” (INSPIRE Thematic Working Group Protected sites, 2010, 1).

It is stated clearly that INSPIRE is primarily concerned with natural protected sites. Even the basic definition of what a protected site is has been taken from that context. What is more, only a very specific part (to many, even minor) of the wider field of cultural heritage may be incorporated into that definition: that of the geographical locations protected, or regulated, for their cultural value by some legal, administrative procedure. This, as arguable as it may be for many heritage experts, delimits the domain at which an INSPIRE derived data model must be considered.

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Although sites of cultural value are explicitly included in those definitions of what constitutes an INSPIRE Protected Site, the corresponding data specification has been developed with a strong focus on the specificities of natural protected sites. As has been pointed out, this offers a narrow framework for protected sites as statutory designations (McKeague et al., 2012), focused mainly on attributes regarding legal aspects. The possibility exists to further complement the description and detailed spatial characterization of protected sites by linking them to specific themes listed in Annex III of INSPIRE. For instance, it may be possible to describe in detail some features of a natural place by using the theme Habitats and Biotopes of Annex III. However, no datasets are listed in Annex III that can be related to cultural heritage (save perhaps the theme Buildings, albeit only partially, see INSPIRE Thematic Group Buildings, 2013). This is why we have considered that the development of a specific schema for protected cultural heritage sites is the best option to incorporate this data into the INSPIRE framework. On the other hand, many characteristics of cultural heritage data are common to other protected sites, so their definition is already agreed on in the INSPIRE Data Specification on Protected Sites, although some remarks are necessary to ensure an appropriate application.

In order to develop a specific data model to describe protected cultural heritage sites, with the aim of incorporating cultural heritage information into the INSPIRE schema, it is essential to clarify the place the category Protected Site occupies within cultural heritage, and to explore which additional spatial elements fall within the domain of cultural heritage. This has the purpose of clarifying to what extent, if any, cultural heritage sites differ from other types of protected sites.

3. The spatial components of cultural heritage data

Cultural heritage is a wide-ranging concept which is complex and can often be controversial. It has undergone some substantial changes in conception, scope and definition over time (see for instance Muriel, 2007-8; Vecco, 2010). Its study has traditionally been framed within the scope of many different academic or technical disciplines and skills: history, art history, anthropology, archaeology, museum studies, etc. More recently, and in parallel with discussions about the nature and meaning of cultural heritage, specific fields of practice, such as so-called Heritage Studies, have emerged (Carman and Sørensen, 2009).

Cultural heritage has been commonly considered, at least in the West, as an object of value deserving of care and preservation by public institutions, be they local, regional, national or international (UNESCO is the most outstanding at the latter level). This idea of cultural heritage as a series of valuable things to be protected and preserved, although strongly challenged by recent approaches, is a “commonsense definition”, or the “natural way of thinking about it”, as stated (and criticized) by Smith and Waterton (2009, 12). As arguable and restrictive as it may be, it is rather coherent for INSPIRE, due to its very administrative and official nature, to adhere to such a theoretical conception of cultural heritage.

However, even adhering to a more or less traditional concept of heritage such as this, value is not an intrinsic characteristic of heritage elements (Tainter and Lucas, 1983; Lipe, 1984; Mason, 2002). Particularly when considering it as a legal concept (a series of protected things) it must be acknowledged that heritage is not a collection of things, be they material or not, that can be defined objectively, as one can define for instance what a collection of guitars is. The condition of something as part of cultural heritage is the result of a process of value assignation that can be based on different criteria. Heritage does not exist by itself, it is constructed (Pearce, 2000; Heinich, 2011).

Our proposal is rooted, at its most general and abstract level, on the basic distinction proposed by Parcero-Oubiña and Gonzalez-Perez (forthcoming, see also Gonzalez-Perez and Parcero-

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Oubiña, 2011) between two major classes of elements in Heritage; the so-called primary and derived entities.

Primary entities are those things, either tangible or not, which when perceived are understood without the need to “be explained”, without explicit interpretative processes. A building, a table, a song or a parade are all primary entities. Obviously perception is a culturally-mediated experience, but the point here is that the perception of those entities relies basically on sensory abilities, rather than on a specific knowledge of subjective reasoning.

The character of primary entities is more easily understood by comparing them with the concept of derived entities, those entities whose perception is not direct and obvious, but that are created after an explicit process of interpretation. Consequently, we can only perceive them when they are introduced to us, or we know the logic behind their creation. A cultural landscape, an archaeological site or a UNESCO World Heritage Site are examples of derived entities: rather than seen, they are understood.

The difference between both concepts becomes even clearer if we think in geographical terms. The geometry, the limits of any primary entity, such as a building, may be equally detected by anyone, since it is embedded in the entity itself. However, the geometry, the extent of something like a cultural landscape is completely dependent on the criteria that have been followed to define it, and different subjects may argue for different versions of what that geometry should be.

This does not mean that derived entities are more intangible, abstract or less material than primary ones. The difference lies in the processes that bring them into existence. Gonzalez-Perez and Parcero-Oubiña elaborate on the concept of archaeological sites:

“The things that comprise it (walls, floors, pottery, etc.) are what we have just called primary entities, entities whose existence can be perceived by anyone; but the site itself is an interpretative concept built upon the aggregation of some of those entities that are considered to form part of a wider entity. That entity (its limits, both spatial and temporal, its function, etc.) is not understood on its own except when the logics behind its demarcation are explained” (forthcoming, see also González-Pérez and Parcero-Oubiña 2011).

Taking that perspective as a reference, the concept of a protected site finds its place as one of the possible types of derived entities, a subclass of things that are created by a process of value assignation. They typically embrace, or relate to, a series of primary entities, but they are different things. The data model we have developed tries to incorporate both dimensions of heritage sites: the primary entities that are to be protected and the valorization that converts them into protected sites.

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Figure 1. Cultural entities and protected sites as different spatial objects.

In terms of spatial data, a consequence of this is that the geometry of a protected site (based on formal, legal or administrative decisions, as stated in the Data Specification on Protected Sites) is different from the geometry of the real-world phenomena that are protected within it (figure 1). Even if they may be coincident at times, they are completely different realities. As has been suggested by Parcero-Oubiña and Gonzalez-Perez (forthcoming), they can be paralleled to Smith and Varzi’s distinction between fiat and bona fide objects (Smith and Varzi, 2000): while most cultural entities are bona fide objects, protected sites are fiat objects. In terms of geometry, Smith and Varzi describe the main difference between them:

“Certainly it may be possible, where one has a fiat boundary in a physical object, to generate a bona fide boundary in the corresponding place, e.g. by cutting. But […] no pre-existent inner surface is brought to light by a process of cutting. Likewise, some national borders will in course of time come to involve boundary markers (barbed wire fences and the like) which will tend in accumulation to replace what is initially a pure fiat boundary with something more substantial. But this is not a process of transformation. The categorical distinction between fiat and bona fide boundaries is absolute” (2000, 409).

In practical terms, the distinction between the real-world phenomenon and the protected site, and their own different geometries, has some further benefits. Let us consider some hypothetical, but feasible, situations:

• Two entities that are objectively equal, or very similar, to each other; for instance, two small Romanesque chapels dating from the 12th century. They can be considered as part of differently valued protected sites. For instance chapel 1 may be protected only by a regional administration, implying that the protected area is restricted to the limits of the building itself, whereas chapel 2 may be considered as a national monument, implying that an area of 50 meters around the building is under protection. However, chapel 1 can be “upgraded” to national monument at any time, thus creating a new protected site on the basis of the same, unchanged real-world phenomenon.

• The condition, form or geometry of a real-world object can change with no corresponding effect on the protected site that encompasses it. For instance, a portion of a building may collapse, totally or partially, but the area subject to protection may remain intact for different reasons.

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• The condition, form or geometry of a protected site can change without any previous modification in the real-world object related to it. For instance, the protected area around a building may be extended, or reduced, for technical, legal or practical reasons, while the building that is protected remains exactly the same.

Therefore, considering cultural entities and protected sites as different, albeit connected, classes has a conceptual foundation, but also practical benefits. Changes in certain attributes of the former (including geometry) do not imply changes in attributes of the latter. Within the proposed model, a cultural entity must be described and mapped just once, although it can be included in many different protected sites (such as local urban planning, a national monument record or a World Heritage Site). This is an additional benefit of the model proposed: it minimizes the effort needed to incorporate information.

The proposal by Gonzalez-Perez and Parcero-Oubiña (2011, forthcoming) considers the existence of some other types of derived entities beyond protected sites. Even some of the things that we are considering here as cultural entities may be defined as having been produced following an explicit interpretative process. Consider, for instance, the examples of archaeological sites or cultural landscapes mentioned above. They may be converted into protected sites, but quite often they are defined within research processes. Seen from that perspective, the concept of cultural entity might be subdivided following that idea. However, INSPIRE is basically concerned with one type of evaluation, that which induces legal protection, so we have chosen here to observe that difference and to let the end user eventually add further detail and distinctions to this point.

As will be noted, our model is not very prescriptive and is highly abstract, so that it may be applied to any temporal or geographical context. However, there is more detail to it than just a mere distinction between legal objects (protected sites) and real-world objects (cultural entities). From the perspective of typical practices in Heritage Management, a rather common way of organizing heritage elements is to follow a widespread disciplinary classification that differentiates Architectural Heritage, Archaeological Heritage and Ethnographic Heritage (e.g. Querol 2010). However, our model does not follow that path. From a conceptual perspective, it does not correspond to a difference in entities, but to the different perspectives from which things are observed and described. It could be argued that a common agreement would allow most entities to be more easily ascribed to one of those “boxes”. For instance, a cathedral could just as easily be described as an architectural entity, as a Neolithic settlement or an archaeological site. However, many cases exist where such ascriptions are deeply arguable, denoting the essentially procedural and conventional nature of such “heritage types”. Take, for instance, the Roman Coliseum; is it an architectural or an archaeological site? Or the Hungarian village of Hollókő; is it an architectural or an ethnographic site?

Despite all of this, our model acknowledges the fact that many protected heritage sites are described in terms of “disciplinary oriented” concepts. To allow the incorporation of that information, if necessary, the model includes a list of values relating to the nature of protection (detailed in Fernández-Freire et al., 2012, Uriarte-González et al., 2013 and Fernández -Freire et al., forthcoming).

A second conventional classification of heritage is that based on the concepts of tangible and intangible heritage and, within the former, of movable and built heritage (e.g. Ahmad, 2006). According to the former distinction, places can be protected due to the existence of material entities or for their relationship with the development of “immaterial” cultural practices. Again, the categorical nature of this difference is rather arguable. In fact, although it is widely accepted and used, the very notion of intangible or immaterial heritage has been actively challenged (Smith and Akagawa, 2008). Among other reasons, it has been argued that any

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form of heritage involves both material and immaterial dimensions (Munjeri, 2004). Again, this is not a categorical distinction, and thus it is not a solid basis to classify heritage.

However, one cannot deny that reality is composed of things of different natures, both tangible and intangible, that are perceived and, consequently, described in different ways and by using different terms (attributes). The fact that both tangible and intangible entities exist as separate concepts in the model (figure 2) does not mean that tangible and intangible cultural heritages could or should exist as separate concepts, nor that tangible and intangible protected sites exist: protected sites are by definition (fiat) tangible things, as long as they consist of portions of land (as opposed to intangible heritage elements such as tales, traditions, festivals, etc.). However, some specific cultural entities are distinctly tangible or intangible, such as a building or a song; this is inherent in their nature, and implies different mechanisms for describing and documenting them.

Figure 2. Simplified UML diagram (no attributes) of the subclasses of CulturalEntity.

What is more, the model allows a protected site to be linked to both tangible and intangible entities, since the relationship is set at an extremely abstract, high level. For instance, a festival that is celebrated in the same church every year can be documented as two different real-world phenomena (the festival as an event, and the church as a building) that are linked to the same protected site, if the place where the event happens is to be protected due to its heritage value.

Denominating cultural entities and protected sites as separate (albeit connected) classes makes the need for a different consideration of both concepts more explicit, and brings the relevance of the spatial component within the heritage elements to the forefront. When dealing with protected natural sites, the value is typically embedded in the place itself that is protected. Characteristics that make a place naturally valuable are inherently attached to their geographical location, and cannot be set apart from each other. A hill, a lagoon or a marshy area, are all natural features that cannot be protected separately from the place where they are located. Rather than being located somewhere, natural places are best described as locations in themselves. This could also be the case with cultural entities. Indeed, the relevance of location and place in the characterization of cultural features has long been claimed in such disciplines as Cultural Geography (for instance Claval, 1995), Anthropology (see Tuan, 1974; or Ingold, 2000) or Landscape Archaeology (for instance David and Thomas, 2008), to name but a few. However, in Heritage Management, locations have been traditionally disregarded as merely contextual, and even circumstantial, attributes of objects and features. When describing cultural features, such as buildings or sites, heritage experts tend to focus on the formal characteristics, with the spatial dimension constituting just another attribute,

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rather than a property. Currently, in terms of preservation, heritage elements are sometimes preserved by removing them from their places of origin. Dealing with the two proposed categories of spatial objects (legal and cultural), allows us to make the different nature of both aspects explicit and to make clear the need for a different process of reasoning in their creation.

The field of cultural heritage has already been subject to the development of conceptual and data models. The CIDOC Conceptual Reference Model (CIDOC CRM) is the most noteworthy (Doerr, 2003; Crofts et al., 2010), thanks to its wide acceptance, especially since it was formulated as an ISO standard (ISO 21127:2006). Although CIDOC CRM includes a number of classes that allow for modeling the location of things (Doerr, 2003), its main objective is to deal with museum collections and not with heritage places. This means that most of the reasoning in CIDOC CRM is aimed at objects; hence geospatial location is not a primary concern. In fact, CIDOC CRM developed a powerful model to describe location, especially in relative terms (Doerr, 2003, 88), which is extremely relevant in describing the changing location of cultural objects, but has a different approach to the INSPIRE one, which is based on spatial geometries.

Apart from that, CIDOC CRM does not take into consideration the difference that we have adopted here between entities and valorizations. Therefore, there it has no good way of incorporating the idea that cultural entities and protected sites should be treated as separate concepts. Nonetheless, it maintains a basic distinction between three kinds of entities that we regard as our primary real-world cultural entities: Man Made Object, Man Made Feature and Site, that we have renamed as HumanMadeObject, HumanMadeFeature and NaturalFeature. The difference between them lies in their link with the natural environment, whether they are completely separate from it, embedded in it or not modified by human action but still culturally significant. As we shall see next, we have incorporated these concepts into the model as classes, in order to guarantee some degree of interoperability with a well-known and widely used standard.

4. Integrating cultural heritage into the INSPIRE framework: an abstract data model

As was previously mentioned, there is no room here to present the full data model we have developed, but just some of its basics, with the aim of showing the practical implementation of the conceptual reasoning developed in the previous paragraphs .

According to the general philosophy and theoretical foundations of the model, as detailed in the previous section, there are three main parts to our proposal, which can be labeled legal, cultural and documentary (figure 3). This distribution enables different ways of extending the model depending on the nature of the implementation required.

The data model and schema were developed to be valid for use in any possible context of documentation of protected heritage sites. For this reason we can identify two basic characteristics:

1. It is highly abstract. It is generic enough to embrace all kinds of heritage data, as long as they have a spatial reference. The model does not define specific types of objects or features. Classes are defined down to a certain level of detail, but any user is free to use whatever classification he/she desires in order to organize their data better. The more specific classes the model defines are those such as “Document”, “HumanMadeObject” or “NonMaterialEntity”. But users are free to classify information below that level as they like, and to use any thesaurus of their choice, on the sole condition that the system used is expressly declared.

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2. It is barely prescriptive. Only a few very basic and general attributes, are defined for some of the classes. Again, users are free to enrich their data documentation by adding as many extra attributes as they wish in any case. In addition, most of the proposed model characteristics are set as voidable (as defined in ISO19103: 14, and specified in INSPIRE Thematic Group Protected Sites, 2010: 7-8). Therefore, different applications might be built to meet the needs of any user community.

In the following sections, we shall offer a brief overview of the three main parts of the model in order to see what kind of information they consider.

Figure 3. General outlook of the UML diagram of the cultural heritage application schema, showing the three main parts further described in the text. Transparent (white) boxes

correspond to classes from the INSPIRE Protected Sites Simple Schema, dark (blue) boxes correspond to classes from the INSPIRE Protected Sites Full Schema, and yellow (light) boxes

correspond to our cultural heritage extension.

4.1 The legal part

Directly dependent on the INSPIRE ProtectedSite class, a new basic class, called ProtectedHeritagePlace, has been designated. This class has been developed as an extension of the more generic class ProtectedSite. It is the main class in the heritage schema, and the only mandatory item. It inherits all the attributes of the ProtectedSite class, making some of its attributes compulsory through the use of a constraint, in an effort to offer a minimum of common information, beyond a simple identifier and a geometry, which is the minimum required by the INSPIRE Data Specification on Protected Sites. The attributes that are made compulsory are: legalFoundationDate, legalFoundationDocument, designationScheme, spatialResolution and beginLifespanVersion (more details in Fernández-Freire et al., forthcoming). It also adds three new attributes: placeName, administrativeScope and type.

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Figure 4. UML diagram showing the class ProtectedHeritagePlace and its relationship with the INSPIRE ProtectedSite classes from the Simple (transparent-white box) and Full (dark-blue box)

schemas.

The nature of protected heritage sites, as previously discussed, allows them to be coherently represented through 2D geometries, as is the case for the INSPIRE ProtectedSite class, that defines a site's geometry based on administrative boundaries. Protected heritage sites are areas of geographical space subject to legal protection, so they can be satisfactorily mapped as 2D polygons.

Implementations of the schema should therefore offer a ProtectedHeritagePlace class containing a series of mandatory attributes including information on issues such as an identifier, the date of legal issue, the type of protected site (such as monument, building, etc.) and, of course, a geometry (figure 4).

The way this class has been designed allows a quite typical situation in heritage management to be dealt with: the implementation of different stages in the protection of the same site. Heritage sites may typically follow a sequence of legal forms that varies the degree of protection, or that are just different stages to be followed throughout the process of legal protection. For instance, in Spain a site may be included in the Registro de Bienes Culturales (national heritage record) first as “launched” (some sort of preliminary stage) and then finally as “inscribed”.

The attributes legalFoundationDate and legalExpiryDate allow this to be dealt with. A site might be recorded as two different legal entities, with the first one (the “launched site”) having both a legalFoundationDate and a legalExpiryDate, whose value coincides with the legalFoundationDate of the second one (the “inscribed site”).

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Furthermore, there are two common issues that might arise when working with Spanish legal heritage elements, and quite possibly elsewhere, that we have tried to solve in the model.

The first issue is the inclusion of several protected heritage sites in the legal definition of a wider protected heritage site. It is usual to refer to different ethnographic, architectonic or archaeological elements that fall within the limits of a larger area, such as a cultural landscape. The self-aggregation relationship named “contains" allows for this kind of behavior, enabling an aggregation of objects of the same class.

The second issue is the usual reference in a legal document to the site’s protected surroundings, which may typically have a different legal condition and degree of protection, but whose existence is inseparably linked to the site itself. As long as the protected surroundings have a different geometry, identifier, area, etc., they should be instanced as a new object of the same class, and referred to through the self-association denominated “protectionSurrounding”.

4.2 The cultural part

One of the voidable attributes in the ProtectedSite class is protectedEntity, that is, the series of actual features protected by the legal entity. This attribute was included in the INSPIRE Protected Sites Full Schema to be completed with a complex object included in Annex III in the case of natural protected entities such as Habitats and Biotopes or Species Distributions. However, as we have seen, cultural heritage is not considered further in INSPIRE, save for the specific case of Buildings, so this is where we have added the most. It is worth stating that the “cultural part” of the model (figure 5) is considered as optional under any circumstances, for the attribute containing all these development bears the voidable stereotype.

Figure 5. UML diagram of the “cultural part” of the data model. Dark (blue) boxes correspond to classes from the INSPIRE Protected Sites Full Schema, yellow (light) boxes correspond to our

cultural heritage extension.

The cultural part is built around the CulturalEntity class, a highly abstract general class designed to include all kind of entities that may be regarded as cultural heritage. As global as it is, it does not depend on size, physical nature or processes of demarcation. It embraces both

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primary and derived elements, as defined in the previous section. A cultural entity might be a small feature such as a wall or a brick, whose existence and geometry are neat and perceived without the need for explicit interpretative processes. Cultural entities can also be larger in size and composed of many smaller elements, for instance a monastery, which is a collection of buildings and annex spaces. In addition, cultural entities can also be elements whose existence depends to a great extent on a subjective judgment, as for instance is the case of a cultural landscape, an aggregation of many singular features that are considered to be part of something bigger and of a different nature. The self-aggregation relationship denominated “aggregates” enables that behavior. Thus, the disaggregation of the elements included in the model depends on the nature of the data gathered by the data provider.

CulturalEntity inherits three attributes from the ProtectedEntityType class, which belongs to the Protected Sites Full Application Schema, and adds five more in order to develop the description of some very basic cultural heritage issues. Three of these attributes are proposed as mandatory (in the event that the documentation of objects of this class is assumed):

• entityName: The name of the entity, which might differ from the name of the protected heritage site it is linked to.

• chronology: All cultural entities have a story that starts at the time they were made and, hopefully, reaches the present day (more on chronology below).

• entityTag: There are many ways to classify cultural entities according to their nature, function, etc. Following the non-prescriptive philosophy of this model, data providers are encouraged to use a classification or thesaurus of their choice (such as UNESCO Thesaurus , The Getty Art and Architecture Thesaurus , English Heritage thesauri , the TPHA (in Spanish) ,…), as long as they specify in this attribute the thesaurus in use and the value adopted for the cultural entity within that thesaurus. The CulturalEntityType class encompasses that information.

In addition to this basic information, two more elements are taken into consideration as voidable attributes: a textual description of the cultural entity (entityDescription) and its spatial definition (geometry). This implies that any cultural entity might have its own geometric definition, differing from that of the ProtectedHeritagePlace that represents the definition of the legal protection. Should this attribute be left blank, only the definition of the legal figure would become available.

The geometric representation of heritage elements has been one of the most hotly debated research issues in recent years, especially following the introduction of 3D recording techniques and tools, such as laser scanners or close range photogrammetry (e.g. El-Hakim et al., 2008, Katsianis et al., 2008, Remondino, 2011). A number of research teams are advancing in various related fields, such as the development of improved tools and procedures for data capture, the creation of 3D repositories and related tools (Doerr et al., 2011), virtual museums and the development of web based 3D tools for non-expert users (Hazlewood et al., 2011).

In fact, and although it could be argued that an accurate 3D representation is useful in many fields, in the case of cultural heritage the detailed and accurate representation of 3D geometries has become essential for the characterization of heritage elements and in aiding the processes of diagnosis and preservation, since the value of heritage elements lies to a great extent in their materiality.

However, the integration of 3D geometries into SDIs is still exceptional in any thematic field (Basanow et al., 2008). So far, only one of the themes in INSPIRE, Buildings, has developed the possibility to optionally manage 3D geometries (INSPIRE Thematic Working Group Buildings, 2013), following the OGC standard CityGML (OGC, 2012). To what extent this could be a good candidate to be extended to the field of cultural heritage has yet to be explored. However, our main focus here is, as we have been describing, the definition of the main classes of spatial

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elements that comprise the domain of heritage and the relationships among them, rather than their description and representation. Therefore, we have adhered here to the 2D geometry that INSPIRE defines for most of the spatial data. Although there is no doubt that objects in this CulturalEntity class demand 3D geometry to properly represent their form and topological relations (as opposed to objects in ProtectedSite, which are satisfactorily represented as 2D geometries), this is beyond the scope of our paper.

Cultural entities are subdivided into different classes in an effort to offer a sound generic framework for any kind of application that might be developed focusing on different aspects of these entities. However, our model will remain at a highly abstract level so that it will be of application in any context and each user will be able to incorporate into it the degree of detail and the specific categories of their choice.

The classification of cultural entities is based on the very basic distinctions previously discussed. On the one hand, between tangible and intangible entities. As we have already discussed, we are using here the concepts of tangible and intangible to refer to the physical nature of things that may be related, grouped and regarded as heritage elements. Tangible and intangible elements are most certainly different in how they are documented, described and spatially recorded. This is the rationale behind the subdivision of the class CulturalEntity into the two subclasses NonMaterialEntity and MaterialEntity. This allows for the separate description and spatial reference of the different types of characteristics, events or manifestations that are considered relevant for the protection of a site.

On the other hand, and at a more detailed level, a new subdivision within the class MaterialEntity is considered, by adopting a classification proposed in the CIDOC CRM (Crofts et al., 2010: 12-13):

• HumanMadeObject: physical features created by human activity which have a physical boundary separating them from other objects. A wall or a building are objects which can be included in this class.

• HumanMadeFeature: identifiable features which are human-altered or made, physically integrated inside other objects, with no clear boundaries separating them. A rock art engraving, a pit or a hypogeous are examples of this type of feature.

• NaturalFeature: pieces of land or sea constituting singularly identifiable features . A forest or a beach are examples of this class.

Finally, we have included another class related to material entities in order to allow the documentation of information related to a widespread practice within the heritage field: the analytical exploration of heritage objects and structures. When the cultural entity is material, many samples may be taken from it in order to determine its nature, condition, state of preservation, date, etc. The class Sample is designed to collect that information, and, in addition, each sample may yield different analytical results, that are to be described in the AnalysisResults class.

4.3 The documentary part

This part has been created in order to allow the inclusion of information resources (documents) referring to cultural entities (figure 6). In this way, the data model can incorporate additional and more developed information about any cultural entity, beyond the basic attributes of its corresponding class (CulturalEntity).

The central class in this part is Document, meaning any kind of resource that contains information about another entity. In our model, the entities described are specifically cultural entities (CulturalEntity). The model considers the twelve specific kinds of documents proposed by the Dublin Core Metadata Element Set.

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Figure 6. UML diagram of the “documentary part” of the data model. All classes correspond to our cultural heritage extension.

4.4 Chronology

As we mentioned previously, chronology is a key issue when dealing with heritage elements, since it often provides a key argument to support the heritage value of an element (no matter how arguable this may be, it has been a long-standing practice in the heritage field). The expression of chronology is an extremely complex issue that, fortunately, has already been subject to detailed exploration. We have relied on the implementation of the standard ISO 19108:2002, which provides a sound schema to expose the timeline of a cultural entity, describing chronology as an element with geometry and topology in a single dimension. The timeline of a cultural entity starts at the moment of its creation and, in most cases, reaches either the present day, or a known moment in the past, marked by a series of events: creation, occupation, abandonment, re-occupation, modification, restoration, etc.

The schema consists of temporal objects that relate to a temporal reference system. Time is treated as a one-dimensional reality so it has geometry and topology, like any spatial dimension. Time objects might therefore be geometric or topological primitives; geometrical primitives provide information about temporal position, while topological primitives provide information on connectivity. There are two primitive geometric classes, instant and period, that relate to the topological primitives, nodes and edges, respectively. An instant is a zero-dimensional primitive that represents a position in time that must be associated to a temporal reference system, while a period is defined by a start and an end instant.

Temporal reference systems may consist of ordinal, temporal coordinate systems, calendar dates or clock times. This means that they can be as accurate or inaccurate as necessary, so data providers may implement a rich and complex chronology referencing events with a precise date or may have nothing more than a rough chronological indication to fill in this attribute (more details in Fernández-Freire et al., 2012, Uriarte-González et al., 2013 and Fernández -Freire et al., forthcoming).

5. Concluding remarks

Cultural heritage is a field which is full of spatial information. Most objects, features or events that are regarded as heritage have a substantial part of their meaning and value attached to the geographical locations in which they occur. Knowing where those elements are placed is a key part of their documentation. In order to properly document and share information on these spatial dimensions we need to embrace well established principles in the realm of spatial information, such as interoperability.

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What is more, the protection of places due to their heritage value is a widespread mechanism through which significant parts of the geographical space are subject to specific restrictions or regulations, the accurate and updated knowledge of which is essential for policy and decision making.

Integrating cultural heritage elements into the wider field of spatial information seems desirable to us in an attempt to help fulfill those needs. Doing this within a wider framework such as INSPIRE may guarantee the success and wider impact of such an effort.

We expect that the data model, whose conceptual foundations and basic structure have been presented in this paper, may contribute to that end: to fulfill the implementation of spatial heritage data within the INSPIRE framework, and to develop interoperability rules that will enable the harmonization and sharing of heritage information. We also hope that the open nature and rather abstract condition of the model (i.e., not proposing specific types of heritage objects, but rather high level classes) will help to build bridges between datasets created and maintained in different environments, by different types of agents and with different interests in mind: public administrations, research institutions, museums, but also the general public, a relation that holds great potential in supporting policies and activities that have an impact upon our widely cultural environment. At the same time, that open and abstract condition of the model allows further extensions and developments in specific areas, such as the afore-mentioned incorporation of a 3D Application Schema.

Acknowledgements

As was mentioned above, the initial steps of the work presented here were taken within a Thematic Sub-group of the Spanish SDI Working Group. The authors wish to acknowledge the following members of that sub-group for their contribution (in alphabetical order): Tomás Abad Balboa, Emilio Abad Vidal, Pilar Chías Navarro, Marta Criado Valdés, Mercedes Farjas Abadía, Francisco García Cepeda, Miguel Lage Reis-Correia, Javier Márquez Piqueras, Victorino Mayoral Herrera, Juan Luis Pecharromán Fuente, Arantza Respaldiza Hidalgo, María Ruiz del Árbol Moro, Antonio Vázquez Hoenhe and José Julio Zancajo Jiménez.

We would also like to thank Sebastián Mas Mayoral and Antonio Rodríguez Pascual for the possibility of developing this work inside the Spanish SDI Working Group (GT-IDEE).

Thanks to Elías López-Romero for his revision of the French version of the abstract.

This work has been partially supported by the Spanish Government through the projects “Investigación en tecnologías para la valoración y conservación del Patrimonio Cultural” (CONSOLIDER INGENIO 2010 CSD2007-00058) and SPATRIAL-“Definición de un Modelo para la Representación de Aspectos Espaciales del Patrimonio” (HAR2009-1226, Programa Nacional de I+D+I, Ministry of Science).

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