Contextualization via Qualifiers - Leitura de Artigo

Peter F. Patel-Schneider:
Contextualization via Qualifiers. CKGSemStats@ISWC 2018

Sarven Capadisli, Franck Cotton, José M. Giménez-García, Armin Haller, Evangelos Kalampokis, Vinh Nguyen, Amit P. Sheth, Raphaël Troncy:
Joint Proceedings of the International Workshops on Contextualized Knowledge Graphs, and Semantic Statistics co-located with 17th International Semantic Web Conference (ISWC 2018). CEUR Workshop Proceedings 2317, CEUR-WS.org 2018

Abstract. 

A common method for contextualizing facts in knowledge graph formalisms is by adding property-value pairs, qualifiers, to the facts in the knowledge graph. 

[Afirmações contextualizadas e não fatos]

Qualifiers work well for information that is additional to the base fact but pose an unwarranted burden on consumers of the information in knowledge graphs when the qualifier instead contextualizes the base fact, as in limiting the applicability of the fact to some time period or providing a confidence level for the fact. 

[Pq seria um fardo injustificável? Economia cognitiva?]

Contextualization should instead by done in a more principled manner and accompanied by tools that lessen the burden on consumers of knowledge graphs.

[Haveriam dois tipos de qualificadores: os aditivos e os contextuais. Os aditivos se aplicam a relações n-arias e especificam um papel]

Additive Qualifiers

In Wikidata there are qualifiers, adding extra information directly to the statements that represent facts. In schema.org there are roles, which interpose an extra item between the subject and object to which additional information about the relationship can then be added. Singleton properties is an extension to RDF that adds special property nodes that can then hold additional information about the relationship they represent. RDF itself has reification, where a statement node represents a triple and can be used as the subject of additional information about that triple.

[Várias abordagens para incluir qualificadores aos statements]

In each case the additional information can be considered to qualify the base fact. In each of these methods the qualifying information is, in principle, unrestrained, representing anything from additional arguments to the relationship (such as the role played by a cast member or the administrative district of a government position) to location information (such as the location in which a fact holds) to temporal information (particularly the temporal period in which the fact holds).

[Argumentos ou entidades adicionais da relação n-ária não seriam qualificadores e nem contexto. Como diferenciar?]

It is important to note that the reification of a triple in RDF does not entail the triple, i.e., it is possible to have the reification of a triple in RDF without implying that the triple itself is true so there is no implication from the above that Gone with the Wind has Clark Gable as a cast member, nor that he plays Rhett Butler in the movie.

[Além do número de triplas adicionais, esse também é um problema da reificação]

Wikidata is built around items and property-value statements about them, thus forming in essence subject-predicate-object facts. Each statement can have associated qualifiers, which are predicate-object pairs. ... Here the underlying “triple” is indeed a fact, as opposed to the situation with RDF reification, but, as Wikidata does not have a formal semantics, there is no formal statement of this intended meaning.

[Falta de uma semântica formal no modelo WD]

This extra information does not interfere in any way with the cast membership, so tools (and queries) that are interested in cast membership can safely ignore the qualifier so long as they handle the modifications to the underlying data structure to handle qualifiers.

[Essa informação adicional não interfere na avaliação se afirmação é falsa ou verdadeira assim como ser útil, ou seja, não contextualiza a afirmação e sim complementa]

Contextual Qualifiers

However, many, perhaps most, uses of qualifiers in Wikidata and schema.org contextualize the underlying fact, i.e., they limit the contexts in which the underlying fact is true. One of the most important contextualizations is temporal contextualization, which is generally handled in these schemes via a start and end qualifier.

[No caso de qualificadores contextuais, os mesmos permitem delimitar o escopo no qual as afirmações são verdadeiras]

3 The Problem with Contextual Qualifiers

The underlying problem is that contextual information does not add to the base information but instead modifies the it, stating in which context (temporal or otherwise) the information is true or providing information as to how likely the base information is to be true. Consumers of the information need to always be aware of whether the context that they are (perhaps implicitly) working in is not one to which the qualifiers attached to a particular piece of information apply.

[A melhor resposta possível é sempre contextualizada, ou seja, as afirmações são recuperadas junto com os qualificadores e contextos associados]

This might not be so hard if the only contextual information is temporal and that information is carried only by start and end dates. Tools (and queries against the underlying data) working in a particular time point can explicitly exclude facts with temporal qualifiers that do not cover that time point. Tools (and queries) working in an implicit now can exclude any fact with an end time qualifier (assuming of course that no end date is in the future, which could be a requirement for temporal qualifiers).

[Contexto explícito na consulta ou contexto implícito e default da aplicação]

However, each and every contextual qualifier has to be considered by every tool (and query against the underlying data). So there can be multiple exclusions, such as for contextual location, confidence, and certainty, and tools (and queries) will have to be updated whenever new such qualifiers are added. Wikidata has over one hundred and fifty qualifiers so to determine whether a fact is true in a context in Wikidata each and every one has to be examined to see if it is a contextual qualifier and for those which are their interaction with the current context or the implicit context has to be determined. This is a high bar indeed, made even worse as new qualifiers are added on an ongoing basis.

[O modelo de KG Contextualizado tem o mapeamento dos qualificadores que representam dimensões contextuais e esse modelo pode ser "lido" pela aplicação]

4 Solutions for Contextual Qualifiers

The right solution is to not show contextual qualifiers to consumers. Ideally, instead replace contextual qualifiers with a formal theory of the contexts so that basic tools (contextualizers, reasoners) can be written that correctly take context into account. Alternatively, create low-level tools that remove facts that are not valid in the contexts that a consumer wants to use.

[Exibir ou não os qualificadores durante a busca exploratória pode ser uma decisão / configuração da interface mas a melhor resposta sempre recupera os mesmos]

........

Context semantics: Relating contexts

Context is distinguished from data by semantics: by expressing some meaning that cannot be captured in the data semantics.

We should worry less about representation and more about semantics and applications.

[Operações entre contextos como por exemplo hierarquia de assuntos em contexto temático, se a afirmação está associada ao tema A1 que é filho de A então também está associada ao contexto do tema A. Ou em um contexto de Localização se uma afirmação (sobre legislação) é válida em um estado então é válida para todos os municípios do estado mas não funciona no vice-versa. ]