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Left Corner
In formal language theory, the left corner of a production rule in a context-free grammar is the left-most symbol on the right side of the rule. Patrick Blackburn and Kristina Striegnitz, Natural Language Processing Techniques in Prolog For example, in the rule ''A→Xα'', ''X'' is the left corner. The left corner table associates to a symbol all possible left corners for that symbol, and the left corners of those symbols, etc. Given the grammar :S → VP :S → NP VP :VP → V NP :NP → DET N the left corner table is as follows. Left corners are used to add bottom-up filtering to a , or top-down filtering to a |
Formal Language Theory
In logic, mathematics, computer science, and linguistics, a formal language consists of words whose letters are taken from an alphabet and are well-formed according to a specific set of rules. The alphabet of a formal language consists of symbols, letters, or tokens that concatenate into strings of the language. Each string concatenated from symbols of this alphabet is called a word, and the words that belong to a particular formal language are sometimes called ''well-formed words'' or ''well-formed formulas''. A formal language is often defined by means of a formal grammar such as a regular grammar or context-free grammar, which consists of its formation rules. In computer science, formal languages are used among others as the basis for defining the grammar of programming languages and formalized versions of subsets of natural languages in which the words of the language represent concepts that are associated with particular meanings or semantics. In computational complexity ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Production (computer Science)
A production or production rule in computer science is a '' rewrite rule'' specifying a symbol substitution that can be recursively performed to generate new symbol sequences. A finite set of productions P is the main component in the specification of a formal grammar (specifically a generative grammar). The other components are a finite set N of nonterminal symbols, a finite set (known as an alphabet) \Sigma of terminal symbols that is disjoint from N and a distinguished symbol S \in N that is the ''start symbol''. In an unrestricted grammar, a production is of the form u \to v, where u and v are arbitrary strings of terminals and nonterminals, and u may not be the empty string. If v is the empty string, this is denoted by the symbol \epsilon, or \lambda (rather than leave the right-hand side blank). So productions are members of the cartesian product :V^*NV^* \times V^* = (V^*\setminus\Sigma^*) \times V^*, where V := N \cup \Sigma is the ''vocabulary'', ^ is the Kleene star o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Context-free Grammar
In formal language theory, a context-free grammar (CFG) is a formal grammar whose production rules are of the form :A\ \to\ \alpha with A a ''single'' nonterminal symbol, and \alpha a string of terminals and/or nonterminals (\alpha can be empty). A formal grammar is "context-free" if its production rules can be applied regardless of the context of a nonterminal. No matter which symbols surround it, the single nonterminal on the left hand side can always be replaced by the right hand side. This is what distinguishes it from a context-sensitive grammar. A formal grammar is essentially a set of production rules that describe all possible strings in a given formal language. Production rules are simple replacements. For example, the first rule in the picture, :\langle\text\rangle \to \langle\text\rangle = \langle\text\rangle ; replaces \langle\text\rangle with \langle\text\rangle = \langle\text\rangle ;. There can be multiple replacement rules for a given nonterminal symbol. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Top-down Parser
Top-down parsing in computer science is a parsing strategy where one first looks at the highest level of the parse tree and works down the parse tree by using the rewriting rules of a formal grammar. LL parsers are a type of parser that uses a top-down parsing strategy. Top-down parsing is a strategy of analyzing unknown data relationships by hypothesizing general parse tree structures and then considering whether the known fundamental structures are compatible with the hypothesis. It occurs in the analysis of both natural languages and computer languages. Top-down parsing can be viewed as an attempt to find left-most derivations of an input-stream by searching for parse-trees using a top-down expansion of the given formal grammar rules. Inclusive choice is used to accommodate ambiguity by expanding all alternative right-hand-sides of grammar rules. Simple implementations of top-down parsing do not terminate for left-recursive grammars, and top-down parsing with backtracking may ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bottom-up Parser
Bottom-up may refer to: * Bottom-up analysis, a fundamental analysis technique in accounting and finance * Bottom-up parsing, a computer science strategy * Bottom-up processing, in Pattern recognition (psychology) * Bottom-up theories of galaxy formation and evolution * Bottom-up tree automaton, in data structures * Bottom-up integration testing, in software testing * Top-down and bottom-up design, strategies of information processing and knowledge ordering * Bottom-up proteomics, a laboratory technique involving proteins * Bottom Up Records, a record label founded by Shyheim * Bottom-up approach of the Holocaust, a viewpoint on the causes of the Holocaust See also * Bottoms Up (other) * Top-down (other) * Capsizing, when a boat is turned upside down * Mundanity, an precursor of social movements * Social movements, bottom-up societal reform * Turtling (sailing) In dinghy sailing, a boat is said to be turtling or to turn turtle when the boat is fully invert ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
