In this paper we investigate the problem of XML Schema evolution. We first discuss the different kinds of changes that may be needed on an XML Schema. Then, we investigate how to minimize document revalidation, that is, detecting the document parts potentially invalidated by the schema changes that should be revalidated.

An XML-to-relational mapping scheme consists of a procedure for shredding XML documents into relational databases, a procedure for publishing databases back as documents, and a set of constraints the databases must satisfy. In previous work, we discussed two notions of information preservation for mapping schemes: losslessness, which guarantees the complete reconstruction of a document from a database; and validation, which guarantees that every update to a database corresponding to a valid document results in a database corresponding to another valid document. Also, we described one information preserving mapping scheme, called Edge ++, and showed that, under reasonable assumptions, lossless and validation are both undecidable. This leads to the question we study in this paper: how to design information-preserving mapping schemes. We propose to do it by starting with a scheme known to be information preserving (such as Edge ++) and applying to it equivalencepreserving transformations written in weakly recursive ILOG. We study a particular incarnation of this framework, the LILO algorithm, and show that it provides significant performance improvements over Edge ++ and that the constraints it introduces are efficiently enforced in practice. 1

The use of word operations has led to fast algorithms for classic problems such as shortest paths and sorting. Many classic problems in stringology, notably regular expression matching and its variants, as well as edit distance computation, also have transdichotomous algorithms. Some of these algorithms have alphabet restrictions or require a large amount of space. In this paper, we improve on several of the keys results by providing algorithms that improve on known time/space bounds, or algorithms that remove restrictions on the alphabet size. 1

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 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. Key words: PACS:

Abstract. As XML schemas evolve over time or as applications are integrated, it is sometimes necessary to validate an XML document known to conform to one schema with respect to another schema. More generally, XML documents known to conform to a schema may be modified, and then, require validation with respect to another schema. Recently, solutions have been proposed for incremental validation of XML documents. These solutions assume that the initial schema to which a document conforms and the final schema with which it must be validated after modifications are the same. Moreover, they assume that the input document may be preprocessed, which in certain situations, may be computationally and memory intensive. In this paper, we describe how knowledge of conformance to an XML Schema (or DTD) may be used to determine conformance to another XML Schema (or DTD) efficiently. We examine both the situation where an XML document is modified before it is to be revalidated and the situation where it is unmodified. 1

We study the problem of storing XML documents using relational mappings. We propose a formalization of classes of mapping schemes based on the languages used for defining functions that assign relational databases to XML documents and vice-versa. We also discuss notions of information preservation for mapping schemes; we define lossless mapping schemes as those that preserve the structure and content of the documents, and validating mapping schemes as those in which valid documents can be mapped into legal databases, and all legal databases are (equivalent to) mappings of valid documents. We define one natural class of mapping schemes that captures all mappings in the literature, and show negative results for testing whether such mappings are lossless or validating. Finally, we propose a lossless and validating mapping scheme, and show that it performs well in the presence of updates. 1 1

Applications in pervasive computing are typically required to interact seamlessly with their changing environments. To provide users with smart computational services, these applications must be aware of incessant context changes in their environments and adjust their behaviors accordingly. As these environments are highly dynamic and noisy, context changes thus acquired could be obsolete, corrupted or inaccurate. This gives rise to the problem of context inconsistency, which must be timely detected in order to prevent applications from behaving anomalously. In this paper, we propose a formal model of incremental consistency checking for pervasive contexts. Based on this model, we further propose an efficient checking algorithm to detect inconsistent contexts. The performance of the algorithm and its advantages over conventional checking techniques are evaluated experimentally using Cabot middleware.

Abstract. The W3C XML Schema recommendation defines the structure and data types for XML documents. XML Schema lacks explicit support for timevarying XML documents. Users have to resort to ad hoc, non-standard mechanisms to create schemas for time-varying XML documents. This paper presents a data model and architecture, called τXSchema, for creating a temporal schema from a non-temporal (snapshot) schema, a temporal annotation, and a physical annotation. The annotations specify which portion(s) of an XML document can vary over time, how the document can change, and where timestamps should be placed. The advantage of using annotations to denote the time-varying aspects is that logical and physical data independence for temporal schemas can be achieved while remaining fully compatible with both existing XML Schema documents and the XML Schema recommendation. 1

The inclusion of Regular Expressions (REs) is the kernel of any type-checking algorithm for XML manipulation languages. XML applications would benefit from the extension of REs with interleaving and counting, but this is not feasible in general, since inclusion is EXPSPACE-complete for such extended REs. In [9] we introduced a notion of “conflict-free REs”, which are extended REs with excellent complexity behaviour, including a cubic inclusion algorithm [9] and linear membership [10]. Conflict-free REs have interleaving and counting, but the complexity is tamed by the “conflict-free” limitations, which have been found to be satisfied by the vast majority of the content models published on the Web. However, a type-checking algorithm needs to compare ma chine-generated subtypes against human-defined supertypes.

The process of creation of document-centric XML documents often starts with a prepared textual content, into which the editor introduces markup. In such situations, intermediate XML is almost never valid with respect to the DTD/Schema used for the encoding. At the same time, it is important to ensure that at each moment of time, the editor is working with an XML document that can enriched with further markup to become valid. In this paper we introduce the notion of potential validity of XML documents, which allows us to distinguish between XML documents that are invalid because the encoding is simply incomplete and XML documents that are invalid because some of the DTD rules guiding the structure of the encoding were violated during the markup process. We give a linear-time algorithm for checking potential validity for documents. 1.