We consider the structural descriptions produced by various grammatical formalisms in terms of the complexity of the paths and the relationship between paths in the sets of structural descriptions that each system can generate. In considering the relationship between formalisms, we show that it is useful to abstract away from the details of the formalism, and examln the nature of their derivation process as reflected by properties of their derivation trees. We find that several of the formalisms considered can be seen as being closely related since they have derivation ee sets with the same structure as those produced by Context-Free Grammars. On the basis of this observation, we describe a class of formalisms which we call Linear Context- Free Rewritin Systems, and show they are recognizable in polynomial time and generate only semilinear languages.

Introduction This note shows preliminaries of the hedge automaton theory. In the XML community, this theory has been recently recognized as a simple but powerful model for XML schemata. In particular, the design of two schema languages for XML, namely RSL(Regular Schema Language) and DSD (Document Structure Description) , is directly based on this theory. 2 Hedges First, we introduce hedges. Informally, a hedge is a sequence of trees. In the XML terminology, a hedge is a sequence of elements possibly interevened by character data (or types of character data); in particular, an XML document is a hedge. A hedge over a finite set E (of symbols) and a finite set X (of variables) is: (1) e (the null hedge), (2) x, where x is a variable in X, (3) a(u), where a is a symbol in E and u is a hedge (the addition of a symbol as the root node), or (4) uv, where u and v are hedges (the concatenation of two hedges). Figure 1 depicts three hedges: a{e), a{x), and a{e)b{b{e)x). Observe that el

We describe the SVP data model. The goal of SVP is to model both set and stream data, and to model parallelism in bulk data processing. SVP also shows promise for other parallel processing applications. SVP models collections, which include sets and streams as special cases. Collections are represented as ordered tree structures, and divide-and-conquer mappings are easily defined on these structures. We show that many useful database mappings (queries) have a divide-and-conquer format when specified using collections, and that this specification exposes parallelism. We formalize a class of divide-and-conquer mappings on collections called SVP-transducers. SVP-transducers generalize aggregates, set mappings, stream transductions, and scan computations. At the same time, they have a rigorous semantics based on continuity with respect to collection orderings, and permit implicit specification of both independent and pipeline parallelism. 1 Introduction Achieving parallelism in bulk data...

We address the problem of tight XML schemas and propose regular tree automata to model XML data. We show that the tree automata model is more powerful that the XML DTDs and is closed under main algebraic operations. We introduce the XML query algebra based the tree automata model, and discuss the query optimization and query pruning techniques. Finally, we show the conversion of tree automata schema into XML DTDs.

. The finiteness of ranges of tree transductions is shown to be decidable for TBY + , the composition closure of macro tree transductions. Furthermore, TBY + definable sets and TBY + computable relations are considered, which are obtained by viewing a tree as an expression that denotes an element of a given algebra. A sufficient condition on the considered algebra is formulated under which the finiteness problem is decidable for TBY + definable sets and for the ranges of TBY + computable relations. The obtained result applies in particular to the class of string languages that can be defined by TBY + transductions via the yield mapping. This is a large class which is proved to form a substitution-closed full AFL. 1 Introduction The finiteness problem is one of the classical decidability problems in formal language theory. For a given language of interest, one usually does not wish to know whether that language is finite (because it usually is not), but rather whether the l...

In this paper we propose a type-based framework for using logic programming for XML processing. We transform XML documents into terms and DTDs into regular types. We implemented a standard type inference algorithm for logic programs and use the types corresponding to the DTDs as additional type declarations for logic programs for XML processing. Due to the correctness of the type inference this makes it possible to use logic programs as an implicitly typed processing language for XML with static type (in this case DTDs) validation. As far as we know this is the first work adding type validation at compile time to the use of logic programming for XML processing.

Unfortunately, the class of transformations computed by linear extended top-down tree transducers with regular look-ahead is not closed under composition. It is shown that the class of transformations computed by certain linear bimorphisms coincides with the previously mentioned class. Moreover, it is demonstrated that every linear epsilon-free extended top-down tree transducer with regular look-ahead can be implemented by a linear multi bottom-up tree transducer. The class of transformations computed by the latter device is shown to be closed under composition, and to be included in the composition of the class of transformations computed by top-down tree transducers with itself. More precisely, it constitutes the composition closure of the class of transformations computed by nite-copying top-down tree transducers.

Structure definitions of documents have been used successfully for inputting and formatting in text processing systems. This report considers transformations between different representations of structured documents and studies possibilities to extend the use of structure definitions to document transformations and to discover algorithmic methods for carrying out transformations. Documents are presented as parse trees for context-free grammars and transformations are made from parse tree to parse tree. First, the report describes differences of manuscript styles required by various scientific journals and presents a declarative classification for structure differences between two parse trees. Second, a set of tree transformation methods are described and their suitability for transformations between documents having a structure difference in each defined class is analyzed. For each class several methods may or must be used and only certain kinds of differences can be managed automatica...

Explanation-based learning (EBL) systems have established their applicability to a wide variety of tasks. However, in despite intensive research, several problems relating to explanation-based learning have remained by and large open. This paper describes an approach to the problems of generalizing number and learning efficiently from multiple examples. The basic insight upon which the technique is based is that EBL can be thought of as learning control knowledge for a theorem-prover. By providing a richer representation for such control knowledge, more general rules can be learned: in particular, by providing looping constructs, rules which generalize number can be expressed; and by providing conditional branches, rules learned from different training examples can be combined. The technique described has been fully implemented, is domain-independent, and has been applied to a number of examples from the domain of VLSI circuit design.

. A software system called Treebag---Tree-Based Generator---is presented. The aim behind Treebag is to allow for the generation and visualization of objects of all kinds: pictures, trees, graphs, strings, numbers, etc. The basic principle is that tree generators like, for instance, regular tree grammars, generate terms over symbols that are interpreted by appropriate algebras as operations on the domain of objects under consideration. Thus, every term is viewed as an expression that denotes one of the objects of interest. These objects can be visualized using appropriate displays. 1 Introduction In mathematics and computer science, one of the most natural and universal ways to denote elements of a given data space is to use expressions over a suitable set of operations, like p 3=7 + 5. The usefulness of this concept is even strengthened by the fact that such an expression may contain variables---in which case it does not denote a particular, single object, but a set of objects or a ...