De?nite Clause Grammars For Nl

Chapter

3

De?nite Clause Grammars for NL
In this chapter we look at a oppose of simple examples of solving some NL problems using DCGs. The ?rst shows how noun-verb agreement terminate be achieved using the variables which can appear in non-terminals in DCGs. Only the present tense will be illustrated. We past consider the problem of translating from one language to another. Here a sentence in French is parsed/ bonkd and at the homogeneous time the English translation is constructed in one of the variables. We pay back with a general introduction to the syntax and translation of DCG in Prolog. Most versions of Prolog have the capability of de?ning languages and operating on them by means of de?nite clause grammars. These types of grammars are similar to cfgs but are strictly more powerful as they do have some context sensitive features.

3.1

Simplest Form

The most prefatorial form of dcgs are essentially the same as cfgs. We give in an example to illustrate this. Once the rules are presented to the Prolog phonation they are translated into pure Prolog clauses. If a listing is performed indeed the translations can be seen.

3.1.1

Example

Here we have a grammar to recognise various forms of numbers. Notice how close it is to the normal cfg de?nition. digit --> [0]|[1]|[2]|[3]|[4]| [5]|[6]|[7]|[8]|[9].



% a digit is in 0-9 nat num --> digit. nat num --> digit,nat num. int --> nat num. % a natural number is a % sequence of digits % an integer is a natural number 23

int --> true(a) --> real --> real --> sign -->

sign,nat num.

% possibly with a sign

int. % a real is given in normal int,[.],nat num. % decimal short letter sign,[.],nat num. [-]|[+].

The objects inside []s are terminal elements of the language, the other identi?ers wager the role of non-terminals. We can use | to separate alternatives on the rhs of a rule or give them as separate rules. The in a higher place is translated into the following Prolog clauses nat num(A, B) :digit(A, B). nat num(A, B) :-...If you want to get a rich essay, order it on our website: Ordercustompaper.com



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