LOTED2: An ontology of European public procurement notices

2.1. LOTED ontology

The LOTED ontology4

Although the LOTED ontology satisfies the requirement of usability and is very suited to the purpose for which it has been designed, it does not actually represent knowledge about the domain, as it merely defines the structure of data objects in the domain. However, authors were aware of this aspect and a more expressive representation of the domain of procurement was planned as part of future work on the LOTED project. The LOTED2 ontology has been developed to achieve this goal.

LOD26

At the heart of this infrastructure there is the Public Contracts Ontology (PCO). The authors state they are not interested in modeling every aspect related to a contract, but only “information which is available in existing systems on the Web” and “which will be usable for matching public contracts with potential suppliers” [34]. In other words, the goal of this ontology is to model a public contract as a whole, but without going into details of the domain.

PCO is more articulated than LOTED: it is not built to model the data structures of a particular system (TED), but rather tries to represent a variety of aspects of the domain, taking into account the integration with other ontologies (Good Relations, VCard,8

Nevertheless, PCO shows some weaknesses that cannot be ignored, even while keeping in mind that it is not a legal ontology. In particular, the ontology aims to provide a conceptual description of both the tendering phase and the phase of the execution of the contract. However, there is not a clear conceptual distinction between these different scenarios in the PCO. Indeed, in the ontology the different concepts of call (call for tenders, such as contract notice) and contract (public contract) are often confused.

First of all, the class pc:Contract is modeled as subclass of the “Call for Anything” class c4n:Call. In some sense, a contract notice (not a contract) can be considered as a ‘call’, a call through which it is announced a competitive bidding for the award of a public procurement contract. In other words, a contract notice is a call-for-tenders, which may be submitted for the award of a public procurement contract. Thus, the contract is ‘the stakes’ of the competitive bidding announced through a notice (i.e. a call), not the call itself. Secondly, the Contract so modeled in PCO has both an estimated and actual price, at the same time. When the notice is published the price is only an estimated one. The final price will be set only at the end of the competitive bidding, on the basis of the award criterion (for an example the lowest price) and of the tender bids submitted. So, it would be appropriate to keep strictly separate the different phases of contract notice publication from the tendering phase, from the award phase of the contract and then from its execution.

Conceptual confusion increases by defining the Class pc:Contract as equivalent to the Class loted:Tender.11

Summarizing, this ontology tackles complex subjects through a too simplistic approach.

‘10ders Information Services’12

Basically, the commercial services offered to small and medium enterprises span from tenders alerting systems on the basis of the subscriber profile model, to the offer of reports on the major public buyers for their products and services. It also provides a customized data mining analysis of public procurement tailored to the interest of each client.

Aside from the commendable purpose to provide an unique access point (‘a pan-European platform’) both for EU relevant tender notices published on TED, and for notices below EU threshold published on a wide range of buyer profiles of national, regional and local levels, it should be considered that there are many services providing mail alerts about tenders and other mechanisms of this kind. However, the novel approach of this project is that the platform system is built using structured open data instead of screen-scraping techniques.

From the same research academic group (WESO) comes also the MOLDEAS (‘Methods on Linked Data for E-procurement Applying Semantics’) work [2]. This project can be considered as a broader framework, which includes also the experience gained in developing Euroalert.net. Indeed, MOLDEAS aims to apply the Semantic Web and Linked Open Data approaches to public procurement notices, defining a set of goals. The first goal is to transform government controlled vocabularies such as CPV,14

The main advantages claimed by authors of Euro-alert and MOLDEAS are essentially the decrease of information dispersion (arising from the different sources where contract notice above and under EU threshold are published); the unification of data models and formats and the support to multilingual issues (through EUROVOC resources used for the enrichment of public procurement notices). An ontology about public contracts is still in development, as part of WESO group’s future work.

Looking at existing work on ontologies of public procurement domain, there is no mistaking the fact that these artifacts are suitable to be employed in Semantic Web applications. However, as mentioned above, these ontologies do not really take into account the legal aspect of the domain. This is not a fault in itself, provided the domain is described in accordance with the conceptualization dictated by the legal sources.

It is also interesting to note that none of the considered work shows a reference to legal ontologies. Given that public procurement is a legal domain, it might be worth asking why legal ontologies and the Linked Data world are so distant. A brief survey on legal ontologies and an analysis of the peculiarities related to the legal knowledge representation may help to clarify the background.

The larger group of legal ontologies developed up to now, can be classified as two diverse categories.

The first is represented by core legal ontologies, namely ontologies that draw largely on legal theory in order to extract general patterns for describing the main concepts of legal knowledge: agents, roles, norms, normative effects (such as obligations, permissions and prohibitions) and temporal properties (e.g., about normative rules validity, efficacy). Examples of this type of ontologies are: the LRI-Core ontology[8], DOLCE+CLO (Core Legal Ontology) [22], the Ontology of Fundamental Concepts [40] and LKIF-Core [32].

The second group of legal ontologies is represented by specific legal domain ontologies, i.e., conceptualizations of a particular field of legal knowledge drawn from authoritative sources such as national or European laws (e.g., concerning privacy, intellectual property, copyright, etc.). Examples are the IPRONTO ontology [17], the Copyright Ontology [23], the Customer Complaints Ontology [33], the Consumer Protection Ontology [44].

The aim of core legal ontologies is to provide an interoperability framework from which other legal ontologies could inherit general categories, and in that way trying to overcome also comparative and multilingualism issues, among diverse legal systems. On the other hand, legal domain ontologies are built with a specific application-perspective in mind, usually grounded in closed systems. As a consequence, they are focused on the reasoning potentialities more than on the integration with other ontological resources in the open, heterogeneous and large scale Semantic Web environment.

The experience gained so far shows that to deal with the complexity of legal knowledge through ontologies and within the limitations of the Semantic Web languages, requires an intensive design process. Legal ontologies are usually made of a significant amount of axioms and restrictions upon classes, which represent legal concepts, even because of rigid conceptual constraints featuring the legal domain. In fact, the conceptualisation of the legal domain depends on legal sources, which dictate the semantics of legal categories through – more or less precise and explicit – definitions and descriptions, in that way constraining the interpretations (or, at least, part of them).

In contrast, the domains described by the ontologies widely used by the Linked Data community, like for example FOAF18

First of all, legal knowledge cannot be bridled into propositional structures (atomic propositions and propositional connectives): the truth preservation in law does not make sense, because categories of true or false cannot be applied to normative propositions. Secondly only a small part of legal knowledge may be expressed through propositional logic, which is not adequate to support legal reasoning [39]. The reason is that the first step of legal reasoning is to identify a legal concept, and the utility of ontological legal concept representation is precisely to provide a way to classify individuals.

Given this background, we have the impression that there is ‘no room’ for legal ontologies in the Linked Data scenario, where lightweight ontologies like FOAF or Good Relations seem to rule the scene. Because of their characteristics, legal ontologies look set to dedicated and closed systems, to perform complex tasks, but not of integrating themselves into the Web of Data. Nevertheless, some features of legal ontologies are not necessarily incompatible with Linked Data requirements.

On the one hand, the representation of legal concepts and relations among them is useful to verify and fix the correctness of Linked Data statements on legal content, through the use of reasoners such as Hermit [42] or Pellet [43]. On the other hand, the new triples generated, i.e. inferred or materialized, can be written back into the RDF model, adding a new level of granularity in the data. This type of information is just what is useful to drive the integration of ontologies with other related ontologies and datasets.

There are still grounds, however, for asking whether the structural diversity among legal ontologies and the common Linked Data models represents an obstacle to the realization of legal Semantic Web applications and, when needed, to the integration of legal ontologies with other kinds of semantic resources. If so, it is not trivial to figure out how the shift towards a new way of conceiving legal ontologies may be attained. The work we are going to describe here, namely the LOTED2 ontology, can indirectly be considered as an ‘experiment’ carried out having in mind these questions, and thus, trying to give them an answer.

LOTED2 has been designed for the following specific purposes:

to express the (main) legal concepts of the domain of public contract notices as defined in legal sources (European Directives on public contracts);

3.2. Methodology used for building LOTED2: A backward path in re-constructing the procurement data semantics

Two main Directives cover the European public contracts domain: the Directive 2004/18/EC20

These two legal sources represent the reference point to derive the exact meaning of terms used to describe the procurement domain, and to extract the information needed to build any logical theory which would formalize the domain knowledge. Besides this fundamental consideration (albeit an obvious one), another aspect concerning the European tender notices published on the TED system must be taken into account. According to the Directives, the tender notices sent by contracting authorities/entities to the European Commission shall be formulated in accordance to standard forms.22

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Fig. 1.

Tenders Electronic Daily tabular summary of Contract notice n. 382532-2011.

When there are standard forms for drafting a certain type of document, these can be used as starting point for the analysis of each individual document drafted according to the established format. In a certain sense, model forms are descriptions of classes of documents and, each new document drafted, is an instance of one of these classes. The analysis of these model forms may tell us information about the terms identifying parts of the document and the interrelationships among each other. In many cases those terms identify ontological classes and the structural relationships between terms can be considered as object properties or data-type properties. Thus, filling out a new document means the creation of new instances for each class.

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Fig. 2.

Excerpt of a standard form for contract notices.

On the other side, we can derive the exact meaning of terms contained in standard forms only through the analysis of the authoritative sources: the sources of law, indeed, contain the definitions of the relevant terms pertaining to the domain they cover (explicit knowledge), and at the same time, they provide us with information about the nature of legal concepts: what are their features (or properties) and their relations with other concepts, in the whole context of the domain (implicit knowledge). The first is a plain literal analysis, the latter, instead, is the result of a deeper domain-expert’s interpretation.

As extensively discussed (among others) in [11], various approaches and methodologies have been adopted in legal ontology engineering: in particular, ontologies which rely on the interpretation of the sources of law usually are built following a top-down approach; constrastingly, ontologies which rely on textual analysis of legal texts are built following a bottom-up approach.

It is well known, even by the legal ontological engineering community [19], that both approaches show points of strengths, as well as some weaknesses. Legal ontologies built following a top-down approach, may be reused across different application scenarios, because they provide conceptual frameworks generic enough for being reused or specialized by other ontologies. However, legal ontologies built following such an approach may be not adequately linked to textual sources or to real data structure, since they usually contain many theoretical (or legal foundational) definitions.

Instead, following a bottom-up approach (e.g. by extracting a vocabulary from standard forms and analyzing only the syntactic relations among terms), it is possible to discover useful terminological information at a larger scale and in an easier way. However, most of the times, following a bottom-up approach, the obtained result is too detailed, typically described by means of propositional logic. As a consequence, it becomes extremely difficult to discover fine-grained abstractions concerning broader legal concepts and, at the same time, the risk of inconsistency increases. Moreover, the bottom-up approach does not help in discovering and, then, representing more complex legal conceptual structures, which are necessary to emulate the legal reasoning.

Taking into account all these premises, the design approach of LOTED2 is based both on a top-down approach (extraction of legal concepts from legal sources) and on a bottom-up one (analysis of standard forms). We believe that, given the existence of different kinds of textual sources (standard-forms and legal sources) in the domain of interest, in this way it is possible to achieve a better match between language and conceptualization, and then, a good level of correspondence between terms, which identify data, and ontological classes.

Consider for example, the excerpt of the tabular summary related to the contract notice n. 382532-2011 (see Fig. 1) the data ‘AA’, labeled ‘Type of Authority’ (which in this specific case is a ‘body governed by public law’), is extracted from the entries of the standard form as shown in Fig. 2.

Then, an analysis of the Directives is conducted in order to search definitions or other kind of information pertaining to the “Type of Authority” record (or ontological class), especially by analyzing why this kind of information is relevant and why it must be included in contract notices. In this specific case, a definition of types of authorities empowered to issue contract notices is contained in the the Article 1 no. 9 of the Directive 2004/18/CE. This specification is relevant because these types of authorities, by issuing a contract notice, play the role of ‘contracting authorities’. If one relies only on the tabular summary or on the standard form analysis, it is not clear that ‘type of authority’ and ‘contracting authority’ are different types of ontological categories, the latter being a role.

In a certain sense, such a mixed approach facilitates the re-construction of the procurement data semantics, by following a sort of backward path in discovering, through the help of their normative reference texts, what they really mean.

This path (analysis of data ⇒ analysis of standard-forms ⇒ analysis of legal sources) is documented inside the LOTED2-core ontology, through the annotation properties. In fact, a comment (rdfs:comment) is attached to the majority of classes, object and data properties, in order to indicate the legislative reference which has been taken into account for the purposes of the ontological analysis and, specifically, for the definition of that class, object property and data property.

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Fig. 3.

Dependencies between LOTED2-core modules and external ontologies (GoodRelations4Tenders and VCard) in LOTED2-extended.

However, the semi-structured data rendered by the TED system represent only the essential part of all the information contained in these documents. Other relevant information is lost. This is the case, for example, when a proposal for the acquisition of similar or related supplies/works/services may result in contracts being awarded at the same time in the form of separate lots. Since in some cases, economic operators may submit an offer for a single lot only (in those cases in which it is admitted a partial type of bid, for example) this type of information may be very helpful for participation in tenders of SMEs. An XML standard for legal documents, which allows also RDFa assertions in order to link the structural part of the text with ontological classes, such as AkomaNtoso [3,46] or CEN Metalex [6], may be used in order to tag the full content of tender documents.

4.1. Procurements Subjective Scope

The Procurements Subjective Scope module describes the classes of legal persons who are empowered to issue a tender notice (generally called ‘call for tenders’) and to award a public procurement contract, i.e. to play the role of awarding legal entities. An enumeration of these entities is contained in art. 1 (9) Directive 2004/18/EC and in art. 2 of Directive 2004/17/EC. The first type of entities may play the role of contracting authorities; the second type of entities may play the role of contracting entities. Although both the Directives refer to ‘contracting authorities’ and ‘contracting entities’ as two different types of entities, these terms denote, from an ontological point of view, roles rather than types of entities.

Consider for example the case of a body governed by public law, that, on the one hand, issues a notice for the award of a public contract and, one the other, may submit a tender bid in a tender announced by another entity.23

However, for the purposes of the European legislator, the distinction between types of entities, which may play the role of contracting authority, and entities, which may play the role of contracting entities, is very relevant. From this distinction, in fact, depends the application of Directive 2004/18/EC (on ordinary sectors) or of Directive 2004/17/EC (on utilities sectors). Hence, LOTED2 includes two classes that refer to intermediate legal concepts, namely ‘entity operating in ordinary sectors’ and ‘entity operating in utilities sectors’. If an entity falls in the class of the first type of entity, then it may play the role of contracting authority. Instead, if an entity falls in the second type, then it may play the role of contracting entity. The definition of these classes is based on the main activity carried out by an entity. A detailed list of ordinary sector activities and utilities activities is obtained by standard forms, but should not be considered as a numerus clausus (i.e. not limited in their number and content). By means of an annotation property (Loted2:tedLabel) each type of these activities and each type of legal person who issues a notice is annotated with the corresponding TED data’s label. This annotation property is provided with the purpose to drive the user in the implementation of the ontology by using the TED data as instances.

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Fig. 4.

WTO Members and observers in the Government Procurement Agreement (source: Wikipedia).

The Procurement Subjective Scope module is connected to the Tender Document module through the object property Loted2:issues. This module describes the majority of tender documents available on the TED system, issued by the entities defined in the Directives. The aim of this module is to provide a full description of tender documents, which represent notices. Other types of tender documents such as ‘specification’ or ‘descriptive tender documents’ are described because they are strictly related to tender notices. These documents are attached to a contract notice in order to describe in details the type of service, good or works and the manner in which the competitive bidding is conducted.

Data contained in the tabular summaries of TED are basically related to tender notices. So, this module, more than others, has been built emphasizing the bottom-up approach. As in the Procurement Subjective Scope module, also in the Tender Document module the annotation property Loted2:tedLabel is used. Another annotation property, Loted2:tedDataID is used for providing a reference to the ID of the data to which a data-type property refers.

4.3. Procurement regulation

This module describes the legislative sources that regulate the public procurement domain. Apart from the Directives, many other legislative sources regulate the European procurements domain. The most important is the Government Procurement Agreement (GPA), a pluryilateral treaty signed by a number of WTO (World Trade Organization) parties (Fig. 4), with the purpose to open up as much as possible public procurement business to international competition [7,16]. The scope and coverage of GPA is based on the type of procurement, the type of entity and the monetary threshold defined in Appendix I of the Agreement.

It is worthwhile to emphasize that signatories may negotiate the coverage of GPA with other parties, on the basis of reciprocity. For example, the utilities sector is not covered by GPA with respect to Canada and there are many limitations with respect to USA and Japan too, just to name the most relevant. This means that we cannot consider the GPA as a unique treaty for each signatory, since there are rather many bilateral agreements (Canada-EU, USA-EU, et.) negotiated by parties under the GPA framework. Thus, simply saying that a tender is within the coverage of the GPA is not enough to clarify the geographical scope of the application of each single bilateral agreement to the single contract notice. These significant divergences in the application of GPA entail a considerable complexity in defining which specific regulation covers a tender document.

Unfortunately TED system data do not provide an effective help in this direction since they are articulated in an incoherent manner. In fact the field of ‘Regulation’ data is referred once to the political geographical area of the country in which the entity that issued the tender notice is based (European Union, European Economic Area); once to the type of authority that issued the notice (European Investment Bank, European Bank for Reconstruction and Development, European Monetary Institute, European Institution/Agency or International Organization); once to the reason for which the notice is issued (External aid and European Development Fund) and finally once to the actual regulation, although not always identified with the exact wording (Agreement between the European Community and the Swiss Confederation, GPA, etc.).

The Procurement Regulation module of LOTED2-core ontology aims to provide the right interpretation of TED ‘Regulation data’, i.e. which legal source covers the single tender document. This type of information is necessary to define the jurisdiction of the regulation, namely the geo-political reference within the norm is applied and its effects are binding [9,25]. An additional module covering this aspect will be part of our future work.

4.4. Procurement competitive process

A notice is issued by an entity acting as contracting authority or contracting entity in order to announce a competition. There are many types of competitions, based on the type of notice. The most relevant type of competition is the tender (i.e. the competitive bidding) that is announced through a contract notice (but not only). Instead, a design contest is announced through a design contest notice. A qualification system is announced through a notice on the existence of this type of system, that we can consider as a competitive procurement process. This system, in fact, is used by only entity operating in utilities, for seeking qualified economic operators, which meet predefined qualification criteria that must be satisfied by potential providers of specific types of works, services and supplies. An applicant of this type of notice, which satisfies these criteria, is registered in the system as potential candidate or contractor for the particular type of contract. A notice on the existence of a qualification system with call for competition is a notice through which is announced both a qualification system and a tender, in which may participate only operators recognized as qualified according to the system.

A procurement competitive process takes place with an established administrative procedure, the award procedure that can be of different types (open, restricted, negotiated, etc.). LOTED2-core ontology does not describe award procedures.

4.5. Subjective legal situations

This module describes roles played by agents in procurements competitive processes and in organizations. As highlighted in the description of the Procurements Subjective Scope, terms such as Contracting Authority or Contracting Entity denote roles rather than types of entities. In particular they denote roles than only certain entities may play: only entities operating in ordinary sectors may play the role of contracting authority while only entities operating in utilities sectors may play the role of contracting entities. The two terms indicate basically the same concepts, namely a property that an entity assumes when awards a public contract and when carries out all the set of actions required for the awarding process of a contract. The first action is to issue a notice.24

So, by issuing a contract notice certainly an entity starts to play the role of awarding legal entity. Apart from the role of awarding legal entity, this module of LOTED2 enables us to describe also roles played by ‘business entities’ in the competitive processes of procurements, and in organizations. For example, a natural or legal person (operating on the market as ‘economic operator’) who has submitted a tender bid for the award of a proposed public contract is a natural or legal person who plays the role of ‘tenderer’. And if this agent has submitted the best tender bid, then assumes the role of ‘successful tenderer’. Another important aspect in procurements’ role modeling deserves to be emphasized. Just as a body governed by public law may play the role of both awarding legal entity and tenderer, so business entities may play many roles in different procurements competitive processes.

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Fig. 5.

Subjective Legal Situations and Roles in LOTED2-core.

Consider that the eligible customers of many business entities are public authorities and so their core activity is precisely the participation in tenders, even more than one at the same time. Then, this matter is not trivial. In order to represent also these cases, the described module represents (legal) situations more than simply roles. An agent may have more than one subjective legal situation that is related to a role played in a context. In the case of procurement the context is the procurement competitive bidding. These concepts and relationships have been modeled reusing and adapting the ‘Social Reality pattern’ [30,31], one of the proposed content patterns available from the catalogue of Ontology Design Patterns initiative [20,21].

Since LOTED2 is an ontology of public procurement notices, it does not represent public contracts per se. In fact, LOTED2 aims to describe the semantics of notices concerning the award of public contracts and not that of public contracts in themselves. A contract notice is the means whereby a competitive bidding for the award of a public contract is announced. So, the commitment of the ontology is to capture the information of public contract to be awarded (or proposed contract) not of the public contract awarded or in its execution. For this reason, the ontology specifies the class of Loted2:ProposedContract rather than of Contract.

Consider the case in which the tender has been declared unsuccessful: can we speak about a contract or not? Of course not, because the contract has not been awarded and then has not been signed by parties. So, in the stage of notice publication there is not a contract, but a contract to be awarded. This is also clear if we consider that a contract notice is also known in legal doctrine as invitatio ad offerendum, namely an invitation to make an offer for a proposal of contract. And only the successful bidder will be party of the contract. The connection between the contract notice (the invitatio ad offerendum) and the proposed public procurement contract module is via a property chain: Loted2:throughWhichIsAnnounced o Loted2:forAwardOf ⊑ Loted2:throughWhichIsAnnouncedTenderForAward. Every contract or proposed contract has an object, namely the subject matter of the contract. A law-full object is an essential of a contract or proposed contract. According to legal doctrine, object of contract can be intended either as the commitment that parties agree to assume (and the consequently transfer or creation of rights and/or modification or settlement of existing bonds) or as the description of the real object (good or service) to which relates the contract (i.e. the substantial content of the contract) [5].

The analysis of standard forms for contract notices and of the other tender documents shows that the object of contract is intended in the second sense, i.e. as a description of the type of good, service or work that the entity issuing the notice seeks. A rather significant aspect of procurement domain is the division of proposed public contract in lots. In some cases and under certain conditions, entities issuing a contract notice for the acquisition of similar or related supplies/works/services may decide to split the proposal into separate single proposed contracts to be awarded with the same tender. These single proposals that are also parts of a general proposal are called lots.

Since in some cases, economic operators may submit an offer for a single lot only (namely in all the cases in which is admitted a partial type of bid) this type of information may be very helpful for participation in tenders of SMEs. In fact, usually a small enterprise is specialized in one particular sector with one main offering and so it might be interested in bidding for the single lot rather than for the global proposal. Therefore, one of the commitments of LOTED2 ontology is to accurately model this particular aspect of the domain, namely lots, even by ensuring that through ontology were made possible certain inferences.

Lots are proposals of contract as well as proposal of contracts not divided into lots, but they are different in the sense that they depend – in the sense of existential dependence – by the general proposal which include them. At the same time, the general proposal is also a particular one, since it is ontologically dependent on its parts (lots, indeed); otherwise it would be empty with respect to the object of the contract. In other words, there is an ontological mutual dependence between them. Furthermore, the lot and the general proposal share the same nature: they are both proposal of contract. On the other hand, lots are also different and independent from each other, because they have different subject matter and they can be awarded to different tenderers. Therefore, it is not easy to understand if their being part of another proposal should be understood in the sense of composition or in the sense of constitution. So, being aware of this subtle distinction, we have decided to represent it into the ontology by introducing different values (named individuals) of ‘type of proposal’ (see in the ontology the class ProposedContractType), namely Lot, ProposedContractNotDividedIntoLots and ProposedContractDividedIntoLots. Only the first one, namely a proposed contract of type lot, can be part of the latter (in the ontology see the definition of domain and range to the object property isDividedInto and its inverse partOf).

When a proposed contract is divided into lots through the contract notice is announced a tender for award also single lots. Through LOTED2 it is possible to infer that through the same contract notice is announced a tender for award each single lot. This result has been achieved through a set of General Class Axioms combined with property chains.

Two object properties are inferred in order to show which lots will be awarded through the same tender (Loted2: forAwardOf o Loted2:isDividedInto ⊑ Loted2:forAwardLot) and which lots to be awarded are announced through the same contract notice (Loted2:throughWhichIsAnnouncedTenderForAward o Loted2:isDividedInto ⊑ Loted2: throughWhichIsAnnouncedTenderForAwardLot). An example in the published version of LOTED2 ontology shows the inference so described (see individual Loted2:Notice1).

4.7. Tender bid

This module describes the tender bid, namely the offer that may be submitted by the economic operator in the competitive bidding for awarding a public contract. Note that, in english, the same word ‘tender’ denotes the ‘race’, i.e. the ‘competition’ for the public contract, and also the meaning of the offer for a public contract. It is an ambiguous term and, arguably, this ambiguity has led the PCO developers to confuse the ‘race’ with the ‘offer’. For this reason, we have decided to call the offer tender bid, because it is a bid made in the context of a tender. So, the tender bid class aims to describe the offers submitted by economic operators in a tender for the award of public contracts.

An important aspect is that tender bids may be of three different types: a tender bid, indeed, may be either a partial tender bid, a global or partial tender bid, or a global tender bid. In those cases, respectively, an offer may be submitted for exactly one lot, for one or more than one lot, or necessarily for all lots. This feature denotes a sort of quality that a tender bid has in a single tender. Furthermore, a tender bid has only one of these quality in each tender. The type of tender bid is, then, strictly related to the lots’ issue, because both a partial tender bid type and a global or partial type imply the existence of a proposed contract divided into lots; instead the global tender bid type may be admitted both in tenders through which are awarded contracts not divided into lots and in tenders through which are awarded contracts divided into lots.

A tender bid is evaluated on the basis of an award criterion: the lowest price or the most economically advantageous offer. The first is based only on the criterion of price; the second one is based on a set of combined criteria defined by the authority issuing the contract notice. Furthermore a tender bid will be opened in a certain place (defined into the contract notice) and at a certain date-time; and it may be drawn up in a specific EU language or not.

4.8. Business entity

This module describes the class of the entities playing the role of economic operators (to simplify hereinafter called ‘economic operators’). Economic operators are the subjects to whom the invitation to submit an offer for a proposed public contract is addressed. In other words, an economic operator is the potential counterpart of the awarded contract.

However, not every economic operator can sign a public contract. There are several eligibility requirements, based on certain criteria that must be fulfilled by an economic operator in order to participate in a competitive bidding. Another module describing these requirements will be part of our future works. This module describes private legal persons who are business entities, since they assume the legal form of ‘incorporates’, ‘society’, ‘cooperative’, etc. These classes are modeled following the taxonomy of LKIF-core ontology.

4.9. Top

This is an upper module in which are contained abstract classes, even useful to match the LOTED2 ontology with core ontologies and in particular with core legal ontologies, in order to foster interoperability. In particular, many classes of the ‘Procurement Top Classes’ module are modeled following the LKIF-core ontology schema. This relationship between LOTED2-core ontology and LKIF-core is what we call a compromise accepted in designing LOTED2-core ontology. Indeed, as mentioned above, the initial aim of LOTED2 project was to build an ontology of European public procurement notices integrated with both GoodRelations and LKIF-core ontology. However, during the development of the ontology we had to take some decisions about how to integrate the two ontologies, which use not only different patterns of knowledge representation, but also different modalities of language’s use. This, for instance, is the case of the the time representation.

Given the importance of time factor in legal domain, LKIF-core represents time (such as ‘date of publication’) as classes, while Good Relations represents time through data type properties such as xsd:dateTime. As far as we know, for instance, through OWL constructs there is no way to infer that the date of publication of the contract notice, which according to the LKIF ontology is a Class (namely PublicationDate), coincides with the beginning of the validity of the gr:Offering, which, according to the Good Relations model, is represented as a dataType property (validFrom). Therefore, we had to make a choice between the two options, and taking into account the main goal of the ontology, namely the construction of a Semantic Web application aimed at improving the demand and offer in public procurement, we thought that the approach of Good Relations was more suitable for our purposes. Nevertheless, this is just our choice and nothing prevents to take the opposite decision, but in principle it would be not advisable to choose both options at the same time, otherwise the result would be a useless duplication.

Furthermore, we believe that the LKIF-core ontology has been mostly conceived for representing legislative documents and not also administrative documents, such as tender notices. In fact, every legal document is also a legal source and there is not a clear distinction between legislative sources (which are sources of law in the proper sense) and legal sources, such as a contract (or a proposal of contract), which are sources of law only inter partes, i.e. only among the contractual parties. We agree on the fact that even a contract, a proposed contract, a contract notice and in general an administrative document (i.e. a legal document) are, in a broad sense, sources of law, but this representation does not help us in distinguishing clearly between tender documents and the legal sources that regulate them. Given the need in our domain to make explicit the differences between tender documents and norms about EU public procurement, we have introduced the class of Legislative Document, which comprises EU Directives, and the class of Administrative Document, which comprises tender documents.

On the other hand, in GoodRelations, a business entity is a “legal agent making a particular offering” and it can be “a legal body or a person”. This natural language statement is translated in the GoodRelations ontology by representing Organization and Person as SubClasses of BusinessEntity. This ontological representation is obviously instrumental to the needs of e-commerce Semantic Web applications. However, it implies also that all the persons and all the organizations are also intrinsically business entities, and it is obvious that, from the point of view of the legal domain, this ontological representation is not acceptable, neither for LKIF-core, nor for LOTED2-core, because a legal body in the legal domain is not essentially a business entity. Certainly, a legal body can act also as a business entity, but there is something more to it than its buying activity. First: a business entity in the legal domain is only that particular type of organization which is recognized by the law as a business entity, according to well defined criteria. Second: it is hard to accept the idea that, for example, a Parliament, a Ministry or an European Institution are primarily business entities. It is true that they buy products and services in the market, but their buying activity is not the main activity they carry out; it is only an instrumental activity, functional to the achievement of their institutional goals. Third: in general and also from the legal knowledge point of view, natural persons are not primarily business entities.

For all these reasons, LOTED2-extended maintains a sort of ‘conceptual independence’ from both LKIF-core and Good Relations.

In open systems the heterogeneity, the scale, the data quality, the reliability of information raise significant problems of control of the legal effects of heterogeneous linked data, or ‘smart’ data. Moreover, the inequalities in data accessibility affect the right of equal access to core information. Because of this, building Legal Semantic Web applications will require the ability to foresee and to cope with all kinds of risks that may emerge, in order to avoid that the challenge will turn into a danger.

7.2. Semantic interoperability among legal ontologies and Linked Data models

The integration of legal ontologies with ontological resources related to different domains represents a fairly unexplored field. A sort of rigidity, which derives from the fact that authoritative sources drive the conceptual model, characterizes ontologies about legal contents. This rigidity contrasts with the heterogeneity of the Semantic Web, which instead is characterized by a non-unified and non-univocal knowledge representation. Because of these aspects, it is no accident that legal ontologies are mostly conceived in closed systems rather than open ones.

7.3. The value of “little semantics” in the legal domain

The attempt in integrating LOTED2-core and Good Relations shows also other things. On the one hand, through the properties “seeks” and the mirror inverted “offers”, Good Relations represents in an intuitive way the intents of parties when they issue an invitation to treat or a proposal for the conclusion of a contract (an ‘offer’ in legal terms). In a certain sense, Good Relations shows the final part of the legal superstructure behind the terms “seeks” and “offers”. On the other hand, the integration of the LOTED2 ontology with Good Relations shows that also in the legal domain “a little semantics goes a long way” [27]. Nevertheless, it must be emphasized that in the legal domain this little semantics is just the superficial layer of the whole of legal knowledge upstream. Many other relevant legal issues (like that of requirements for the participation in tenders) require an intensive design to be addressed within the limitations of the Semantic Web languages. That is because, in the legal domain, question answering is not only information retrieval. Information retrieval is not enough, since “question requires some deduction or inference before an appropriate answer can be given” and “regulations may contain many different articles about the same topic and one can only assess whether something is permitted or not by understanding the full documentation”. “A rather detailed understanding is required, in particular, because regulations generally contain complex structures of exceptions” [4]. In other words, question answering in the legal domain is not a trivial matter.

7.4. Compliance by design in legal ontologies modeling

The variety of related work about procurements (up to now there are three ontologies of public contracts, including LOTED2, and another is in development) reveals the strong interest of the Semantic Web community in representing legal knowledge. However, the Semantic Web community should consider the matter more carefully and the Legal Informatics community should try to take up the challenge. In this respect, it is worthwhile to emphasize that an exciting research field is emerging on the use of ontologies for checking compliance of legal documents or processes with norms regulating them [12,33], even by combining ontologies with rules formalized through interchange standards specific for the legal domain [37]. Nevertheless, at the same time, the aspect of compliance by design should be more stressed in legal ontology engineering. Ontologies for compliance and ontologies in compliance might be considered as two sides of the same coin.

Nowadays, technologies in general, and even Semantic technologies are causing so many fast and unexpected changes that the Law is under constant and severe pressure. We can not pretend that these major changes do not also require legal solutions and a way to re-think our approach to the legal knowledge. Surely, re-thinking the legal knowledge in the Semantic Web is a challenging task, not at all simple. However, it is worth to face the challenge, starting from the lesson we have learnt so far.