Textual entailment (TE) in

natural language processing Natural language processing (NLP) is an interdisciplinary subfield of linguistics, computer science, and artificial intelligence concerned with the interactions between computers and human language, in particular how to program computers to pro ...

is a directional relation between text fragments. The relation holds whenever the truth of one text fragment follows from another text. In the TE framework, the entailing and entailed texts are termed ''text'' (''t'') and ''hypothesis'' (''h''), respectively. Textual entailment is not the same as pure logical entailment – it has a more relaxed definition: "''t'' entails ''h''" (''t'' ⇒ ''h'') if, typically, a human reading ''t'' would infer that ''h'' is most likely true. (Alternatively: ''t'' ⇒ ''h'' if and only if, typically, a human reading ''t'' would be justified in inferring the proposition expressed by ''h'' from the proposition expressed by ''t''.) The relation is directional because even if "''t'' entails ''h''", the reverse "''h'' entails ''t''" is much less certain.Dagan, I. and O. Glickman. 'Probabilistic textual entailment: Generic applied modeling of language variability'
in: ''PASCAL Workshop on Learning Methods for Text Understanding and Mining'' (2004) Grenoble.Tătar, D. e.a. ''Textual Entailment as a Directional Relation''
/ref> Determining whether this relationship holds is an informal task, one which sometimes overlaps with the formal tasks of formal semantics (satisfying a strict condition will usually imply satisfaction of a less strict conditioned); additionally, textual entailment partially subsumes word entailment.

Examples

Textual entailment can be illustrated with examples of three different relations: An example of a positive TE (text entails hypothesis) is: *text: ''If you help the needy, God will reward you''. :hypothesis: ''Giving money to a poor man has good consequences''. An example of a negative TE (text contradicts hypothesis) is: *text: ''If you help the needy, God will reward you''. :hypothesis: ''Giving money to a poor man has no consequences''. An example of a non-TE (text does not entail nor contradict) is: *text: ''If you help the needy, God will reward you''. :hypothesis: ''Giving money to a poor man will make you a better person''.

Ambiguity of natural language

A characteristic of natural language is that there are many different ways to state what one wants to say: several meanings can be contained in a single text and that the same meaning can be expressed by different texts. This variability of semantic expression can be seen as the dual problem of language ambiguity. Together, they result in a

many-to-many Many-to-many communication occurs when information is shared between groups. Members of a group receive information from multiple senders. Wikis are a type of many-to-many communication, where multiple editors collaborate to create content that is ...

mapping between language expressions and meanings. The task of

paraphrasing A paraphrase () is a restatement of the meaning of a text or passage using other words. The term itself is derived via Latin ', . The act of paraphrasing is also called ''paraphrasis''. History Although paraphrases likely abounded in oral tra ...

involves recognizing when two texts have the same meaning and creating a similar or shorter text that conveys almost the same information. Textual entailment is similar but weakens the relationship to be unidirectional. Mathematical solutions to establish textual entailment can be based on the directional property of this relation, by making a comparison between some directional similarities of the texts involved.

Approaches

Textual entailment measures

natural language understanding Natural-language understanding (NLU) or natural-language interpretation (NLI) is a subtopic of natural-language processing in artificial intelligence that deals with machine reading comprehension. Natural-language understanding is considered an ...

as it asks for a semantic interpretation of the text, and due to its generality remains an active area of research. Many approaches and refinements of approaches have been considered, such as

word embedding In natural language processing (NLP), word embedding is a term used for the representation of words for text analysis, typically in the form of a real-valued vector that encodes the meaning of the word such that the words that are closer in the v ...

, logical models, graphical models, rule systems, contextual focusing, and machine learning. Practical or large-scale solutions avoid these complex methods and instead use only surface syntax or lexical relationships, but are correspondingly less accurate. However, even state-of-the-art systems are still far from human performance; a study found humans to be in agreement on the dataset 95.25% of the time, while algorithms from 2016 had not yet achieved 90%.

Applications

Many natural language processing applications, like

question answering Question answering (QA) is a computer science discipline within the fields of information retrieval and natural language processing (NLP), which is concerned with building systems that automatically answer questions posed by humans in a natural l ...

information extraction Information extraction (IE) is the task of automatically extracting structured information from unstructured and/or semi-structured machine-readable documents and other electronically represented sources. In most of the cases this activity concer ...

, summarization, multi-document summarization, and

evaluation of machine translation Various methods for the evaluation for machine translation have been employed. This article focuses on the evaluation of the output of machine translation, rather than on performance or usability evaluation. Round-trip translation A typical way ...

systems, need to recognize that a particular target meaning can be inferred from different text variants. Typically entailment is used as part of a larger system, for example in a prediction system to filter out trivial or obvious predictions.

References

External links