Carlo Sartiani

XPeer: a self-organizing XML P2P database system

This paper describes XPeer , a zero-administration system for sharing and querying XML data The system allows users to share XML data without significant human intervention, and to pose XQuery FLWR queries against them The proposed system can be used in any application field, being a general purpose XML p2p DBMS, even though its main application is the management of resource descriptions in GRID environments.

Yet another query algebra for XML data

XML has reached a widespread diffusion as a language for representing nearly any kind of data source, from relational databases to digital movies. Due to the growing interest toward XML, many tools for storing, processing, and querying XML data have appeared in the last two years. Three main problems affect XML query processing: path expression evaluation, nested query resolution, and preservation of document order. These issues, which are related to the hierarchical structure of XML and to the features of current XML query languages, require compile-time as well as run-time solutions. This paper describes a query algebra for XML data. The main purpose of this algebra, which forms the basis for the Xtasy database management system, is to combine good optimization properties with a good expressive power that allows it to model significant fragments of current XML query languages; in particular explicit support is given to efficient path expression evaluation, nested query resolution, and order preservation.

Static analysis for path correctness of XML queries

A part of a query that will never contribute data to the query answer should be regarded as an error. This principle has been recently accepted into mainstream XML query languages, but was still waiting for a complete treatment. We provide here a precise definition for this class of errors, and define a type system that is sound and complete, in its search for such errors, for a core language, under mild restrictions on the use of recursion in type definitions. In the process, we describe a dichotomy among existential and universal type systems, which is essential to understand some specific features of our type system.

Types for path correctness of XML queries

If a subexpression in a query will never contribute data to the query answer, this should be regarded as an error. This principle has been recently accepted into mainstream XML query languages, but was still waiting for a complete treatment. We provide here a precise definition for this class of errors, and define a type system that is sound and complete, in its search for such errors, for a core language, under mild restrictions on the use of recursion in type definitions. In the process, we describe a dichotomy among existential and universal type systems, which is useful to understand some unusual features of our type system.

Efficient inclusion for a class of XML types with interleaving and counting

Inclusion between XML types is important but expensive, and is much more expensive when unordered types are considered. We prove here that inclusion for XML types with interleaving and counting can be decided in polynomial time in the presence of two important restrictions: no element appears twice in the same content model, and Kleene star is only applied to disjunctions of single elements. Our approach is based on the transformation of each such content model into a set of constraints that completely characterizes the generated language. We then reduce inclusion checking to constraint implication. We exhibit a quadratic algorithm to perform inclusion checking on a RAM machine.

Linear time membership in a class of regular expressions with interleaving and counting

The extension of Regular Expressions (REs) with an interleaving (shuffle) operator has been proposed in many occasions, since it would be crucial to deal with unordered data. However, interleaving badly affects the complexity of basic operations, and, expecially, makes membership NP-hard [13], which is unacceptable for most uses of REs. REs form the basis of most XML type languages, such as DTDs and XML Schema types, and XDuce types [16, 11]. In this context, the interleaving operator would be a natural addition to the language of REs, as witnessed by the presence of limited forms of interleaving in XSD (the all group), Relax-NG, and SGML, provided that the NP-hardness of membership could be avoided. We present here a restricted class of REs with interleaving and counting which admits a linear membership algorithm, and which is expressive enough to cover the vast majority of real-world XML types. We first present an algorithm for membership of a list of words into a RE with interleaving and counting, based on the translation of the RE into a set of constraints. We generalize the approach in order to check membership of XML trees into a class of EDTDs with interleaving and counting, which models the crucial aspects of DTDs and XSD schemas.

Mapping maintenance in XML p2p databases

Unstructured p2p database systems are usually characterized by the presence of schema mappings among peers. In these systems, the detection of corrupted mappings is a key problem. A corrupted mapping fails in matching the target or the source schema, hence it is not able to transform data conforming to a schema

Processing XML queries and updates on map/reduce clusters

\mathcal{S}_i

Partitioning XML documents for iterative queries

into data conforming to a schema

Linear inclusion for XML regular expression types

\mathcal{S}_j