# What is Syntactic and Semantic Analysis

January 8, 2018

Computers are very fast and powerful machines; however, they process texts written by humans in an entirely mindless way, treating them merely as sequences of meaningless symbols. The main goal of Syntactic and Semantic analysis is to obtain a suitable representation of text structure and thus make it possible to process texts based on their content. This is necessary in various applications, such as spell- and grammar-checkers, intelligent search engines, text summarization, or dialogue systems. Natural language text can be analyzed on various levels, depending on the actual application setting.

### Overview of Syntactic and Semantic Analysis

People have complex thoughts, and they often express their thoughts with complex sentences using natural languages. This complexity may facilitate efficient communications among the audience with the same knowledge base. But on the other hand, for a different or new audience this composition becomes cumbersome to understand and analyze. Analysis of such compositions using syntactic or semantic measures is a challenging job and defines the base step for natural language processing.

Computer and internet has become a part of our daily life for every other need. A huge amount of information is available in the internet in the form of natural language based compositions. Analyzing natural languages would be the greatest help in this regard. Therefore this field carries a great amount of potential, but it has lot to achieve. For example if we need any information on a topic we throw some keywords from that topic in the search engines. As a result we expect to get the most appropriately related information on that topic. Today’s search engines are very efficient but still they only understand everything in terms of keywords based match.

### Definition of Syntactic Analysis

Linguistics is a domain in which language or languages are studied. The notion of language or languages is a common sense notion. In general, it is not sufficient or very informative to define a field of inquiry by naming the common sense entities it studies.

The goal of Syntactic Analysis is to determine whether the text string on input is a sentence in the given (natural) language. If it is, the result of the analysis contains a description of the syntactic structure of the sentence, for example in the form of a derivation tree. Such formalizations are aimed at making computers “understand” relationships between words (and indirectly between corresponding people, things, and actions). Syntactic analysis can be utilized for instance when developing a punctuation corrector, dialogue systems with a natural language interface, or as a building block in a machine translation system.

Syntactic Analysis of a sentence is the task of recognizing a sentence and assigning a syntactic structure to it. These syntactic structures are assigned by the Context Free Grammar using parsing algorithms like Cocke-Kasami-Younger (CKY), Earley algorithm, Chart Parse. They are represented in a tree structure. These parse trees serve an important intermediate stage of representation for semantic analysis.

### Syntactic Parsing

Syntax: provides rules to put together words to form components of sentence and to put together these components to form sentences.

Knowledge of syntax is useful for:

• Parsing
• QA
• IE
• Generation
• Translation, etc.

Grammar is the formal specification of rules of a language. Parsing is a method to perform syntactic analysis of a sentence.

Parsing (Syntactic Structure)

INPUT: Boeing is located in Seattle

OUTPUT:

Figure 1: Syntactic Tree Structure

### Semantic Analysis

Semantic analysis describes the process of understanding natural language–the way that humans communicate–based on meaning and context. Semantics is defined as the study of meaning expressed by elements of a language or combinations thereof. As like syntactic, there are numerous different approaches in semantic exploration of natural language. Intermediate meaning representations are composed for linguistic expressions. Mostly meaning representations are assigned to sentences solely on the basis of knowledge gained from the lexicon and the grammar, this approach is referred as syntax-driven semantic analysis. First Order Logic can also be used to represent a sentence in a language.

Semantic and pragmatic analysis make up the most complex phase of language processing as they build up on results of all the above mentioned disciplines. Based on the knowledge about the structure of words and sentences, the meaning of words, phrases, sentences and texts is stipulated, and subsequently also their purpose and consequences. From the computational point of view, no general solutions that would be adequate have been proposed for this area. There are many open theoretical problems, and in practice, great problems are caused by errors on lower processing levels.

References

[1] “Syntactic and Semantic Analysis and Knowledge Representation”, Faculty of Informatics, available online at: https://www.fi.muni.cz/research/nlp/analysis.html.en

[2] Roxana Girju, “Introduction to Syntactic Parsing”, November 18, 2004, available online at: http://l2r.cs.uiuc.edu/~danr/Teaching/CS598-05/Lectures/Roxana.pdf

[3] Koopman, Hilda, Dominique Sportiche, and Edward Stabler, “An introduction to syntactic analysis and theory”, Unpublished manuscript (2003).

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