Showing papers on "Chomsky hierarchy published in 1990"

The hierarchy of LR-Attributed Grammars

Abstract: The problem of attribute evaluation during LR parsing is considered. Several definitions of LR-attributed grammars are presented. Relations of corresponding attribute grammar classes are analysed. Also the relations between LR-attributed grammars and LL-attributed grammars and between LR-attributed grammars and a class of one-pass attributed grammars based on left-corner grammars are considered.

Implementing the generalized word order grammars of Chomsky and Diderichsen

Abstract: Many of the insights of Transformational Grammar (TG) concern the movability of const i tuents . But in recent versions (Government & Binding, GB; cf. Chomsky, 1982, Sells,1985) the sentence representations (trees) include both the site of the moved constituent and the site from where it has been moved; the original site of the moved constituent is marked as a trace (t) or empty (e, []). In the sentence schema (Field or Position Grammar) developed by the Danish linguist Paul Diderichsen (1946), there are also positions both for the new and the old site of moved constituents. Thus Diderichsen observes that an adverb could introduce or be the fundament of a sentence, in which case the subject np "remains" in its "normal" position after the finite verb (Swedish example: ldag kom pojken; literally: Today came the boy). If the subject np introduces the sentence (Pojken kom idag) its "original" place after the finite verb must be empty (For comparisons between Transformational Grammar and Diderichsen's grammar, cf. Teleman, 1972, Platzack,1986). Under lying both Chomskyan GB grammar and Diderichsen's Field Grammar is a grammatical system which consists of a general word or constituent order schema supplemented with co-occurrence restrictions. This type of system may be called Generalized Word Order Grammar (GWOG), and this paper deals with ways of implementing such a system on the computer using Definite Clause Grammar (DCG;Clocksin & Mellish, 1981), a formalism available in most Prolog versions. Defini te Clause Grammar is a convenient rewriting system with an arrow (-->) familiar to generative linguists. It allows one to state the maximum sequence of constituents (the order schema) to the right of the arrow. A setup of constraining conditions can then be used to prohibit overgeneration. Such restrictions are stated within curly brackets in the Definite Clause Grammar formalism. Constraining conditions may require that certain slots be filled or empty, that a certain variable have a certain value, that certain constituents cannot occur at the same time (co-occurrence restrictions), etc. In addition one may have further conditions which state that a certain constituent is to have a certain functional role, e.g. be the subject or the object of the sentence. Such conditions may be called functional role conditions (f-conditions) as they build a functional structure (f-representation). This structure may be built in a certain slot (as an additional argument) to the left of the arrow. Further conditions may concern the topic (focus), mode, clause type, lacking constituent, etc. of the sentence, and this information may also be gathered as arguments in slots to the left of the arrow. The system to be presented in this paper also incorporates many of the ideas of Referent Grammar (RG; Sigurd, 1987), a :functional generalized phrase structure grammar used in the automatic translation project Swetra (Sigurd & Gawronska-Werngren, 1988). I hereby acknowledge the help of Mats Eeg-Olofsson,

Formal Language and Power Series.

Abstract: Publisher Summary This chapter discusses formal language theory and focuses on a specific tool called formal power series. Formal language theory, together with automata theory, is the oldest branch of theoretical computer science. The chapter discusses the fundamental notions about formal power series and languages. It also various normal forms for grammars. The chapter describes a class of generating devices that are somewhat different from grammars but still equivalent to grammars in the sense that the family of languages generated by the new devices equals the family of recursively enumerable languages. The new devices, called Post canonical systems or Post systems, very closely resemble formal systems in logic. The productions have the shape of inference rules. The family of languages generated by Post systems equals the family of recursively enumerable languages. The chapter discusses Markov algorithms, which resemble the intuitive notion of an algorithm. Viewed as language-defining devices, Markov algorithms are equivalent to grammars and Post systems.