Игорь Волков – Hardware and software of the brain (страница 10)

In the first 2 cases, the first element of the relation expressed by the preposition is the subject. In the third, the whole construct is ellipsis of some relative clause as explained for this particular example.

Long sentences using complicated structures of modern English syntax may usually be dissected into a set of short simple sentences. After that transformation, it becomes clear how humans process such constructs. For the last example, if there are 2 or more tables in the room, we need clarification. Which one? The sentence may be rewritten. 'A table stands in the corner. He moved to this table.'

How do we use this knowledge? There are 2 typical applications: question answering and problem solving. In the first case, the system will retrieve existing data or derive the answer using its inference engine.

In the second, knowledge is used to find an algorithm of solution. Suppose a service robot has got the order: "Bring a bottle of Cola to me." The machine needs to know where it is. The knowledge base contains records which tell that Cola is in the refrigerator which stands in the kitchen. This is enough to calculate the destination for the navigation system.

Words on the sub-sentence level group according to syntax, but also have semantic roles. The same principle works on higher levels. When we read a text sentence by sentence, they produce some ideas in our mind. They may be remembered for later use or exist temporarily just for the process of reading. These ideas may belong to a few different semantic categories.

Facts

If the sentence has a predicate, it denotes some action. 'The corporation A purchased the startup B.' Although, actions may be static. In this case, they denote a state of some object. 'A pear hangs on the tree.' Such sentences immediately add details to the existing picture of the world. Before we remember them, they usually pass the filter of validity. Some facts may be just impossible so should be rejected. Some – negligible. Don't pay attention.

Explanation

If the fact is improbable but still valid, it needs explanation which opens the filter. Oftentimes such facts become especially valuable. Explanation usually reveals the reasons of why it became possible and, as a rule, is intended for temporary use. Although, in thorough reading the person may analyze and remember something from the explanation so as to use it later in similar cases.

Proof

This is a more formalized variant of explanation. Usually it employs logical inference and derives the result from known facts and rules.

Conclusion

Human logics uses rules. They have various facts as conditions in their body. These facts may be either present explicitly in the knowledge base or derived from other rules. Sometimes the needed logical inference may be lengthy so a text may formulate the conclusion for remembering. After that, it becomes a new fact which does not require proof.

Detailing

The first sentence of a paragraph or the heading of a chapter usually creates a new image in perception. The next sentences add details to this image. The next paragraph of the chapter adds the whole of a new image inside the larger image.

Nucleus Language

The nucleus language is a minimally sufficient set of elements for general-purpose communication.

Being explicitly formulated, it has wide variety of applications: human-computer communication, normalization of human texts, language teaching …

A real language consists of this nucleus + general-purpose extension (lexical and syntax synonymy, rare processing functions, etc.) + professional (special) languages.

The elements included are quite different. The most known component is lexicon – some minimal dictionary of the most used words. At the syntax level, these elements are represented by non-terminal nodes of the parse tree which reside between 'Sentence' and 'Word'. Syntax is about word grouping, but this process goes through a few intermediate levels. For English, the hierarchy is: Word -> Phrase -> Clause -> Sentence. The categories may be related to separate words or to sentences. Accordingly, grammar may use parts of speech (noun, verb …) or members of the sentence (subject, predicate …). These categories are not synonyms. Just substantially overlap, but there are differences too. A noun phrase may serve as a subject phrase or direct object. The prepositional phrase requires a separate discussion.

Syntax is not completely detached from semantics. Indeed, parsing using just parts of speech, not words themselves, is preferable, but even parts of speech still have some generalized semantic load. Both prepositions and conjunctions represent some relations. Prepositions – between nouns (or equivalent words). Conjunctions link homogeneous members of the sentence or clauses in compound and complex sentences. Prepositions represent physical while conjunctions – logical relations. Formal logic turned conjunctions of human language into logical functions.

Accordingly, using 'prepositional phrases' is not semantically correct. Each preposition usually requires 2 nouns like in 'a cat with the long tail' -> with(cat, long tail). This draws far-reaching consequences for the whole structure of the sentence. The predicate phrase can contain a prepositional object. 'He took the bread with butter.' -> with(bread, butter) What if there is no direct object? 'He came with his friend.' -> with(he, his friend) In this case, the preposition links its object with the subject. This is not a well formed solution because objects are parts of the predicate phrase and the link goes over the predicate. We can resolve this issue if we abandon the traditional structure sentence(subject phrase, predicate phrase) and replace it with more logicist

predicate(subject, indirect object, direct object, prepositional object, adverbials)

Semantics of such a format is clear. Each sentence represents some action. If nothing changes like in: 'The box stands on the table.', this is just a static action. In any case, the picture is a function of time. The subject is different from objects only by attracting more attention. It is even not required that it should be the actor. 'The apple was taken by his friend.' In passive voice, the subject is the word with the semantic role of the direct object. This is because attention is directed at this object.

Such generalized semantics independent of particular words may be implemented directly in the program while semantical properties of different words require some dictionary. All in all, the following semantically significant elements may be distinguished in the simple sentence. 1. The predicate (verb). 2. Various noun phrases. 3. Adverbs which are not a part of some noun phrase where they modify an adjective. Such adverbs modify the verb. 4. Prepositions and conjunctions. The former represent relations between noun phrases. The latter – between clauses. They also may link homogeneous members of the sentence. Conjunctions work like logical functions in a list.

predicate(subject phrases, prepositional phrases, adverbs) conjunction predicate() …

Besides these basic elements, there are many derivatives. 1. The gerund is a noun-type word created from a verb. 2. The verb also can produce forms which function as an adjective or an adverb. These are participles.

The first noun phrase is the subject. This category should be retained if we want to answer standard human questions. The indirect object is redundant. It may be replaced by the corresponding prepositional object. 'I gave him an apple.' -> 'I gave an apple to him.' The second variant is more reliable for parsing. Only it should be present in the nucleus language. Adverbials may be represented either by a prepositional phrase or by an adverb. The first is often difficult to distinguish from the prepositional object. 'I came with my friend.' 'With' in the prepositional object. 'I lifted it with my hands.' The same in the adverbial of manner. This can be cleared only from low-level semantics. That is, regarding particular words involved. In some cases, it is impossible to distinguish the roles at all. Both are applicable so leaving prepositional phrase in the representation is justified. Then, its semantics should be computed when it is used in inference or question answering. Finally, conjunctions represent relations between simple sentences as clauses.

You see, there are quite a few basic elements. One difference of natural language from programming languages is its universality. It is used both for abstract computations and machine-level programming. Probably these elements represent some very basic operations performed by neural nets. For example, a noun phrase may stand for an image which is a part of a larger construct while prepositions and conjunctions define how these constructs are built of such images. Details of the procedure are defined by the verb in question. Say, if it is intransitive, there won't be any direct object at all. If the verb is transitive and the object is present, the details of object's handling are defined by this verb.