DOI: http://doi.org/10.6092/issn.2532-8816/8174

Abstract

In questo articolo viene presentata una proposta preliminare di ontologia per la rappresentazione dello schema Text Encoding Initiative (TEI). Le motivazioni e i benefici di una versione semantica e machine-readable della TEI sono molteplici: (1) l'interoperabilità semantica tra codifiche di testi comporterebbe la facilitazione dell'interrogazione cross-corpora e l'integrazione di Linked Open Data; (2) la formalizzazione del TEI abstract model apporterebbe migliorie significative in termini di consistenza e soundness. Data la complessità dello schema TEI, viene qui preso in considerazione un consistente ma ristretto sottoinsieme di elementi e attributi. In secondo luogo la meta-ontology EARMARK viene esaminata. In ultimo, vengono forniti alcuni dettagli implementativi.

This article presents the rationale and the proposal of a preliminary architecture of a formal ontology of the Text Encoding Initiative markup language. The reasons to have a formal and machine-readable semantics for TEI are manifold. In the first place, it would have a number of pragmatic and technical benefits, like better support for semantic interoperability in text encoding practices, easier cross-corpora query processing, seamless integration with Linked Open Data ecosystem. In second place, it would give a formalized account of the quasi-formal notion of the TEI abstract model, fostering the consistency and soundness of the TEI model. Given the complexity of the TEI encoding schema, specifying formally such an ontology will be a time consuming intellectual activity: in a first stage, we propose to limit its scope to a well-defined subdomain of the TEI, and to build it adopting pre-existing meta-ontology like EARMARK. The final part of the article gives some preliminary details of this design.

Introduction

The Text Encoding Initiative markup language represents one of the most significant achievements of the Digital Humanities field and is now universally accepted as the standard formalism for the creation of textual digital resources in humanistic research and scholarship. One of the reasons of its success is the fact that it is based on the XML metalanguage, a sound and simple standard for data modeling and serialization.

There are many theoretical, pragmatic and social reasons for the wide and enduring acceptance of the TEI/XML couplet, notwithstanding the many criticisms and shortcomings. For example:

• XML is relatively easy to learn and use compared to other computer languages, especially if the complexity level of the encoding is low or medium;

• XML encoding affordances are similar to those of traditional textual annotation, a familiar practice to the average humanist;

• XML data format is portable (especially in the editing phase) between different platforms;

• XML processing leaves to the user control on the editing process and on the resulting visualizations;

• XML introduces data quality control in text processing via its internal syntax and schema based parsing facilities;

• XML is flexible enough to accommodate a vast range of humanistic users requirements;

• XML has a good ecosystem of related standards and open source applications.

On the other hand, it is worth pointing out that, even if the TEI is an XML based language, its evolution has somewhat led to a certain level of abstraction from that language and, to some extent, from its underlying tree data model. We must remember, in fact, that it is possible to draw a neat distinction in the usage of XML language: it can be adopted as a full-fledged formal modeling language, in which case we accept the underlying tree data model as a good way to formally represent the object domain; but it can also be used as a mere syntax facility, a serialization language that is independent from the actual data model we are using to represent our domain (as it happens in the XML syntax of languages like RDF and OWL). The TEI, in the course of its evolution, has moved from a modeling orientated usage of XML to a syntactic oriented usage of XML.

This progressive shift has been determined on the one hand by the need to represent many not hierarchical features of textuality, and on the other by the quest for a more semantic oriented way of modeling textual features. In fact, the common belief that XML markup expresses semantic information is technically flawed, in that XML per se is only a syntactic language to represent a tree based data model ( ; ).

Starting from the groundbreaking work of Renear, Huitfeldt and Sperberg-McQueen , various efforts to formalize the semantic role of markup languages have been made in the past 20 years ( ; ; ; ; ). However, none of them has reached a mature state and has produced an operational solution, mostly because of the lack of maturity of the enabling formalisms and technologies adopted, and of the lack of support from the community of users. Building on the achievements (and limits) of these previous efforts, we believe that the Semantic Web stack of languages and frameworks could provide a viable and balanced solution to the theoretical and pragmatic requirements for developing a formal semantic component for the TEI.

The rest of this article is devoted to an overall illustration of this proposal, and is divided in three parts that can be conveniently entitled Why, What and How. Each of them tries to answer to some basic questions that give shape to our proposal:

• Why: why do I think that the idea of giving TEI a formal semantics is a good idea, and how could it enhance its expressive power and hence its usefulness for the community?

• What: what in the TEI do I really think can conceivably be formalized in the form of an ontology? How far can we imagine going in this direction?

• How: which are the better technical and formal strategies to build a semantic model of the TEI subset we have identified in the step before?

Why ontologize TEI?

The reasons to have a formal and machine-readable semantics for TEI are manifold. We can divide them into two main categories: technical and pragmatic reasons, that are universally applicable to any XML markup language; and theoretical reasons, that are particularly relevant for the TEI and its domain of application.

What part of the TEI can be ontologized?

TEI scheme as whole is very complex and diverse, the result of decades of work, refinements, extensions, additions; it covers in details many different areas of application. We acknowledge that it is impossible to reduce this fuzzy cloud to a unique formal semantic definition.

Moreover, TEI real usage in the community is largely influenced by pragmatic factors. That is, the intended meaning of the markup in concrete markup acts is determined by the circumstances of usage, the context in which the markup happens, the presuppositions of the encoder himself. This has produced a loose conglomerate of applications, mutually related by a sort of family resemblance (in Wittgensteinian sense). The Guidelines themselves, in spite of the efforts, present errors and inconsistencies partly because of intrinsic difficulties in editing a huge reference book, partly because of some design principles that informed its very development.

It is impossible to reduce to a unique formal semantic definition this cloud. However, we can identify a subset of shared assumptions, a common ground of notions about the role and meaning of TEI markup and the nature of document like objects: this common set constitutes what we could call the core ontology, and can be the object of an ontological formalization.

For many diverse reasons we suggest that prima facie we can assume the TEI simplePrint customization element set as a satisfying approximation of this common ontology ( ; ). The choice to build our formalization effort on the foundations of TEI Simple, is obviously dictated also by practical reasons, but it is not an opportunistic ad hoc choice, as it may seem.

One of the most common definition of computational ontology is: ‘An ontology is a formal, explicit specification of a shared conceptualization’ ( : 184). This definition differs from the original and most known one given by Gruber in that it stresses the ‘shared’ aspect of the conceptualization, that is fundamental for its successful adoption, as Nicola Guarino notes ( : 14):

For practical usage of ontologies, it turned out very quickly that without at least such minimal shared ontological commitment from ontology stakeholders, the benefits of having an ontology are limited. The reason is that an ontology formally specifies a domain structure under the limitation that its stakeholder understand the primitive terms in the appropriate way. In other words, the ontology may turn out useless if it is used in a way that runs counter to the shared ontological commitment. In conclusion, any ontology will always be less complete and less formal than it would be desirable in theory.

TEI Simple has been defined by a group of domain experts that have analyzed the actual usage of markup in some big textual repositories, and have selected and partially organized a set of one hundred or so elements, that can describe all the textual features represented by TEI markup in those documents :

The TEI simplePrint schema […] sought to define a new highly-constrained and prescriptive subset of the Text Encoding Initiative (TEI) Guidelines suited to the representation of early modern print materials, a formally-defined set of processing rules which permit modern web applications to easily present and analyze the encoded texts, mapping to other ontologies, and processes to describe the encoding status and richness of a TEI digital text. Its choice of elements reflected the practices followed in the encoding of large-scale literary archives, notably those produced by the Text Creation Partnership. Practice of other comparable archives such as the German Text Archive was also taken into account.

This process fits perfectly in the refined definition of ontology. Another relevant aspect of the TEI simplePrint definition is that the markup selection process has tried to assign one and only one textual feature to each markup item. This unequivocal definition is useful to assure the fulfilling of the ontological commitment to an intensional specification of the domain required by ontological design ( : 8–9).

This result could be in principle attained adopting different technologies, but a semantic approach has some exclusive pros:

1. it is independent from the implementation;

2. it is more expressive than the average ad hoc solutions;

3. it can take advantage of inference engines’ capabilities to extend or refine the query without previous knowledge of the details of encoding practices.

Point 3) can explain why we could use the notion sonnet in our imagined semantic query, even if it is not explicitly defined and encoded inside the TEI document as such: provided the existence of a TEI ontology defining the notion of poem it would be sufficient to extend that ontology with a sonnet class, that has the restriction of being composed of two quatrains and two triplets.

Another useful application of a sound and well-defined semantics for TEI XML markup is the possibility to define interoperability relationship between TEI data sets and other data and metadata models and languages working directly at the abstraction level of the ontology and not at the level of the documents, or of the XML schema, where lots of difficulties arise.

How: the architecture of the TEI ontology

The last part of this article describes the overall design and methodological rationales of our ontological modeling of the TEI simplePrint. The design requirements for building such ontology are the following:

• the ontology should express at the same time an abstract characterization of TEI simplePrint elements' and attributes semantics and intended meaning and an ontological definition of their structural role in the document;

• the ontology should define a precise semantics of the elements having a clear characterization in the official TEI documentation (e.g., the element "<p>"), while it should relax the semantic constraints if the elements in consideration can be used with different connotations depending on the context (e.g., the element "<seg>"), allowing for further specification by users;

• it should be possible to extend the ontology, reuse it and define alternative characterizations of elements’ semantics without compromising the consistency of the ontology itself;

• where possible existing ontologies or meta-ontologies should be reused.

In accordance with these overall principles, the TEI ontology can be implemented as an OWL 2 ontology based on preexisting and ad hoc defined ontology modules. The specification of markup semantics for the various TEI simplePrint elements is done by means of EARMARK class and properties. The Extremely Annotational RDF Markup ( ; ) is at the same time a markup metalanguage, that can express both the syntax and the semantics of markup as OWL assertions, and an ontology of markup that makes explicit the implicit assumptions of markup languages (and, in particular, of the hierarchy of XML-based languages), providing a finer specification of the properties of markup, up to and including the possibility of toggling on and off the strict hierarchy of XML instantiations.

EARMARK is suitable for expressing markup semantics straightforwardly. However, we want to associate coherent semantics to markup items following precise and theoretically-founded principles. LA-EARMARK is an extension of EARMARK with the Linguistic Act ontology, a module of the Linguistic Meta-Model . LA attempts to provide a formal representation of the fundamental structure of a linguistic act according to the classical semiotic triangle model and providing the OWL 2 formalizations of the notions of:

• linguistic act: any communicative situation including information entities, agents, meanings, references, and a possible spatiotemporal context;

• information entity: any symbol that has a meaning, or denotes one or more references. They can be natural language terms, sentences or texts, symbols in formal languages, icons, or whatever device can be used as a vector for communication;

• meaning: any (meta-level) object that explains something, or is intended by something, such as linguistic definitions, topic descriptions, lexical entries, logical constraints, etc. They can be interpretants for information entities, and conceptualizations for individuals and facts;

• reference: any (set of) individual or fact from the world we are describing. They can have interpretations (creating meanings) and can be denoted by information entities.

In this context, a markup construct can be seen as a kind of information entity with its own expression, and it becomes possible to express and assess facts, constraints and rules about the markup structure as well as about the inherent semantics of the markup elements themselves.

In our ontology any TEI XML element is expressed as an Earmark class earmark:Element. For instance, the TEI <p> element is defined as follows:

            
Prefix earmark: <http://www.essepuntato.it/2008/12/earmark#>
Prefix co: <http://purl.org/co/>
Prefix tei: <http://www.tei-c.org/ns/1.0/>
Class: tei:p a
earmark:Element that
         earmark:hasGeneralIdentifier "p" and
         earmark:hasNamespace "http://www.tei-c.org/ns/1.0"

      
         

If and when we need to identify and characterize semantically some subsets of one element type defined by the schema we introduce appropriate restrictions of its EARMARK class by the way of the properties provided by the Collections Ontology (CO), which defines as OWL classes unordered and ordered collections . The need for this characterization is determined by the fact that in the TEI schema there are many elements that can appear in different regions of the document tree, with distinct functional and semantic roles. The most apparent example is the element <p>, that is used in its ‘proper’ role of designating a block of prose in the textual content of the XML document, as in every context where there is the need to include some free form textual description or metadata – be it inside the subcomponents of the TEI Header or not. In our ontological model we have differentiated those usages of the XML element. For instance, the class of all the elements <p> that occur inside the <text> element and not inside the <teiHeader> is expressed as follows:

            
Class: tei:pText
EquivalentTo:
   earmark:Element that 
   earmark:hasGeneralIdentifier "p" and
   earmark:hasNamespace "http://www.tei-c.org/ns/1.0" and
   co:elementOf some (
      earmark:Element that 
      earmark:hasGeneralIdentifier "text" and
      earmark:hasNamespace "http://www.tei-c.org/ns/1.0")
            
         

The assignment of semantic properties to the XML elements classes defined in EARMARK is expressed by the mean of punning meta-modeling facility introduced in OWL 2 . Punning is a mechanism introduced in order to assign properties to classes, retaining the decidability and tractability of the formalism . This is achieved introducing the possibility to use an Internationalized Resource Identifier (IRI) inside the ontology both as a class name and an individual name, on the base of the context. Adopting punning, the semantic role assigned to one element can be expressed by the way of classes defined in other external ontologies or ontological modules.

The TEI Semantics Ontology (TSO) is the ontological component that specifies the general intended semantics of the TEI elements (e.g., the fact that an element is a paragraph rather than a section, a personal name reference rather than a geographical reference). This component is the core of our modeling effort and its development is still underway. Its definition is based on a typological categorization of the TEI simplePrint elements set, based on their logical function and intended meaning and independently from their structural position in the tree data model underlying the markup language. For the moment, the role of XML attribute has not been taken into account for the definition of this ontological component. The possibility to use EARMARK facilities to specialize element classes partially fulfills the necessity to map specific element/attribute pairs to their intended meaning, but this issue surely needs a deeper analysis and exploration.

The main class of TSO is tso:documentEntity which defines the class of all TEI documents. All the remaining classes are defined as subclasses of this class and are concepts expressed by TEI elements, although there is not a one to one relationship between XML elements and OWL semantic classes.

As is shown in Fig. 3, the overall class hierarchy of this ontology component is divided into three main subclasses:

• tso:documentLevelElement: the class of the elements related to the material document structure. Its subclasses define the features and characteristic pertaining to the text carrier that can be expressed by the XML markup

• tso:metadataLevelElement: the class of the elements related to the metadata of the document

• tso:textLevelElement: the class of the elements related to the textual structure and features modeled by the XML markup. It is farther subdivided into macro textual divisions (peritextual sections, chapters, sections etc.), micro textual blocks (paragraphs, verse, stanzas, epigraphs, abstract, quotations, lists, etc.) and phrase level components (linguistic features, editorial features, emphasis and other kind of distinctive phrases, etc.).

The link between the EARMARK class that identifies a specific element and its related semantic characterization is expressed by applying the punning to that class (so that it becomes an Individual) and then adopting the LA property semiotics:expresses that is used to specify the intensional meaning attributed to a linguistic (and a markup, inter alia) construct. For instance, we can use it to say that the <p> class defined above expresses the structural semantics of being a paragraph in TSO, as follows:

            
Individual: tei:pText
  Facts:
    semiotics:expresses tso:paragraph
            
         

If necessary, the associations of semantics to markup elements can be contextualized according to a particular agent's point of view in order to provide provenance data pointing to the entity that was responsible for such specification. This is possible by means of the properties provided by the Linguistic Act Ontology included in LA-EARMARK that allow to assign agency and responsibility to all these markup-to-semantics relations, as proper linguistic acts done by someone. This feature of the meta-ontology framework provides the possibility of project or even user defined customizations and refinements of the ontology.

Conclusions and further steps

The proposal to adopt a formal ontology approach to define formally the TEI that we have presented here is admittedly a proof of concept. As we have clearly stated, it is probably not possible to provide a complete and sound formalization of the whole TEI, as is pragmatically used by the community. This objective can be attained for smaller or locally defined subsets, as is the TEI simplePrint. Even with this restriction in order to develop a semantic framework that can express all the constraints and conditions that, some substantial refinements and improvements are required, of which the most relevant are:

• introducing in our modeling a complete (as far as possible) definition of the XML attributes (this is a rather complex area, since most attribute in TEI have ambiguous, multiple or undetermined definitions);

• refining and factorizing the TEI Semantics Ontology component;

• extending the ontological modeling to some other subsets of the TEI that are suitable for formalization. Simple is not all, and with appropriate time and work force the ontology can be extended to some other area of the TEI;

• devising an elegant and easy to use formalism to allow for project specific modifications and specializations of the element ontology – to be expressed via ODD – and for document specific idiosyncratic uses of markup.

These improvements are actually out of the scope and even of the possibility of our small research team, and they need a larger and organized research program, that should involve a much larger part of the TEI community.

In the long term, the formalisms we have adopted in our ontological modeling could evolve to become the principal formalization of the Text Encoding Initiative, independent of any serialization. EARMARK allows for expressing structural constraints in an ontologically precise definition, and can even instantiates the markup of a text document as an independent OWL document outside of the text strings it annotates, permitting a native stand-off markup strategy. Through appropriate OWL restrictions it can define structures such as trees or graphs and can be used to generate validity constraints (including contextual constraints currently unavailable in most validation languages). The assessment of ontological properties in the semantic domain is in many ways comparable to validation in the XML domain. Moving from a syntactical perspective to a semantic one – as proposed by EARMARK – opens new perspectives for a general approach to assessment as well.

A key point of such approach is the translation of many markup properties from a syntactical to an ontological level. In the case of XML schema validation, for instance, this means expressing schema definitions as ontology classes and properties; and schema documents as ontology instances and assertions that expresses hierarchies as semantic relations. Starting from an ontological TBox representing the schema and an ABox representing the document, we can then conclude that the document is valid according to the schema if and only if the ABox is consistent with the Tbox .

At this moment, XML is still probably the better strategy to encode digital texts in real word projects for many practical reasons. However, there is no reason for the TEI to be strictly based on it, as it is de facto now. Technical or pragmatic issues should not determine the choice of a formalization. Elena Pierazzo, at the time chair of the TEI Board, in her paper at the TEI conference 2015 in Lyon entitled TEI: XML and Beyond said: The next few years will be crucial for the survival and expansion of the TEI: in order to survive and overcome the new challenges that come with the fast-evolving world of data representation it will have to part ways with XML as a sole technological implementation and while becoming more abstract offer concrete solutions for those problems that have accompanied its whole life. The proposal drawn in this article can represent a small contribution to the TEI to envision the shape of its own future.

References

1. Bauman, S. (2011). Interchange vs. Interoperability. Proceedings of Balisage: The Markup Conference 2011 doi:10.4242/BalisageVol7.Bauman01.

2. Bergman, M. K. (2009). The Fundamental Importance of Keeping an ABox and TBox Split AI ³ Adaptive Information http://www.mkbergman.com/489/ontology-best-practices-for-data-driven-applications-part-2/.

3. Bergman, M. K. (2010). Metamodeling in Domain Ontologies AI ³ Adaptive Information http://www.mkbergman.com/913/metamodeling-in-domain-ontologies/#mm1.

4. Buzzetti, D. (2002). Digital Representation and the Text Model. New Literary History, 33(1): 61–88.

5. Burnard, L. Mueller, M., Rahtz, S. Cummings, J., Turska, M. (2017). An Introduction to TEI simplePrint. http://www.tei-c.org/release/doc/tei-p5-exemplars/html/tei_simplePrint.doc.html.

6. Ciccarese, P. and Peroni, S. (2014). The Collections Ontology: creating and handling collections in OWL 2 DL frameworks. Semantic Web, 5(6): 515–29 doi:10.3233/SW-130121.

7. Ciotti, F., Daquino, M. and Tomasi, F. (2016). Text Encoding Initiative Semantic Modeling. A Conceptual Workflow Proposal. In Calvanese, D., De Nart, D. and Tasso, C. (eds), Digital Libraries on the Move: 11th Italian Research Conference on Digital Libraries, IRCDL 2015, Bolzano, Italy, January 29-30, 2015, Revised Selected Papers. Cham: Springer International Publishing, pp. 48–60 http://dx.doi.org/10.1007/978-3-319-41938-1_5.

8. Ciotti, F. and Tomasi, F. (2016). Formal Ontologies, Linked Data, and TEI Semantics. Journal of the Text Encoding Initiative,9 doi:10.4000/jtei.1480. http://jtei.revues.org/1480.

9. Ciula, A. and Eide, Ø. (2016). Modelling in digital humanities: Signs in context. Digital Scholarship in the Humanities doi:10.1093/llc/fqw045.

10. Ciula, A. and Marras, C. (2016). Circling around texts and language: towards‘ pragmatic modelling’ in Digital Humanities. Digital Humanities Quarterly, 10(3) http://www.digitalhumanities.org/dhq/vol/10/3/000258/000258.html.

11. Constantin, A., Peroni, S., Pettifer, S., Shotton, D. and Vitali, F. (2016). The Document Components Ontology (DoCO). Semantic Web, 7(2): 167–81.

12. Cover, R. (1998). XML and semantic transparency. Cover Pages http://xml.coverpages.org/xmlAndSemantics.html.

13. Davis, M. (2011). The Universal Computer. Natick: Taylor & Francis Inc.

14. Di Iorio, A., Peroni, S. and Vitali, F. (2010). Handling Markup Overlaps Using OWL. In Cimiano, P. and Pinto, H. S. (eds), Knowledge Engineering and Management by the Masses, 6317. (Lecture Notes in Computer Science). Springer Berlin Heidelberg, pp. 391–400 http://dx.doi.org/10.1007/978-3-642-16438-5_29.

15. Di Iorio, A., Peroni, S. and Vitali, F. (2011). A Semantic Web approach to everyday overlapping markup. J. Am. Soc. Inf. Sci. Journal of the American Society for Information Science and Technology, 62(9): 1696–716.

16. Doerr, M. (2003). The CIDOC conceptual reference module: an ontological approach to semantic interoperability of metadata. AI Magazine, 24(3): 75.

17. Dubin, D., Renear, A., Sperberg‐McQueen, C. and Huitfeldt, C. (2003). A logic programming environment for document semantics and inference. Literary and Linguistic Computing, 18(1): 39–47.

18. Eide, Ø. (2014). Ontologies, data modeling, and TEI. Journal of the Text Encoding Initiative doi:doi:10.4000/jtei.1191. https://jtei.revues.org/1191.

19. Golbreich, C., Wallace, E. K. and Patel-Schneider, P. (2009). OWL 2 Web Ontology Language new features and rationale. W3C Proposed Recommendation.

20. Gruber, T. R. (1993). A translation approach to portable ontology specifications. Knowledge Acquisition, 5(2): 199–220.

21. Guarino, N., Oberle, D. and Staab, S. (2009). What is an Ontology?. Handbook on Ontologies. Springer, pp. 1–17.

22. Hitzler, P., Krötzsch, M., Parsia, B., Patel-Schneider, P. F. and Rudolph, S. (2009). OWL 2 web ontology language primer. W3C Recommendation, 27(1): 123.

23. McCarty, W. (2005). Humanities Computing. London: Palgrave Macmillan.

24. Peroni, S., Gangemi, A. and Vitali, F. (2011). Dealing with markup semantics. Proceedings of the 7th International Conference on Semantic Systems. ACM, pp. 111–18 doi:10.1145/2063518.2063533.

25. Peroni, S. and Vitali, F. (2009). Annotations with EARMARK for arbitrary, overlapping and out-of order markup. Proceedings of the 9th ACM symposium on Document engineering. ACM, pp. 171–80 doi:10.1145/1600193.1600232.

26. Picca, D., Gliozzo, A. M. and Gangemi, A. (2008). LMM: an OWL-DL MetaModel to Represent Heterogeneous Lexical Knowledge. Proceedings of the 6th Language Resource and Evaluation Conference.

27. Rahtz, S., Mueller, M., M., Pytlik-Zillig, B., Turska, M. and Cummings, J. (2015). TEI Simple Processing Model Specification. http://htmlpreview.github.io/?https://github.com/TEIC/TEI-Simple/blob/master/tei-pm.html.

28. Renear, A., Dubin, D. and Sperberg-McQueen, C. M. (2002). Towards a semantics for XML markup. Proceedings of the 2002 ACM symposium on Document engineering. ACM, pp. 119–26.

29. Sperberg-McQueen, C. M., Marcoux, Y. and Huitfeldt, C. (2014). Transcriptional Implicature: A Contribution to Markup Semantics. Digital Humanities 2014. Book of abstracts. pp. 360–62 https://dh2014.files.wordpress.com/2014/07/dh2014_abstracts_proceedings_07-11.pdf.

30. Sperberg-McQueen, C., Marcoux, Y. and Huitfeldt, C. (2010). Two representations of the semantics of TEI Lite. Proceedings of Digital Humanities: 7–10.

31. Studer, R., Benjamins, V. R. and Fensel, D. (1998). Knowledge engineering: Principles and methods. Data & Knowledge Engineering, 25(1): 161–97 doi:10.1016/S0169-023X(97)00056-6.

32. TEI Consortium (2016a). TEI P5: Guidelines for Electronic Text Encoding and Interchange, Version 3.0.0, Last Updated on 29th March 2016. http://www.tei-c.org/Guidelines/P5.

33. Tummarello, G., Morbidoni, C. and Pierazzo, E. (2005). Toward Textual Encoding Based on RDF. From Author to Reader: Proceedings of the 9th ICCC International Conference on Electronic Publishing (ELPUB 2005). Leuven: Peeters, pp. 57–63 http://elpub.scix.net/data/works/att/206elpub2005.content.pdf.

34. Turska, M., Cummings, J. and Rahtz, S. (2016). Challenging the Myth of Presentation in Digital Editions. Journal of the Text Encoding Initiative, 9.

Last consultation URLs: 28/11/2018