The amount of data of all kinds available electronically has increased dramatically in recent years. The data resides in different forms, ranging from unstructured data in file systems to highly structured in relational database systems. Data is accessible through a variety of interfaces including Web browsers, database query languages, application-specific interfaces, or data exchange formats. Some of this data is raw data, e.g. images or sound. Some of it has structure even if the structure is often implicit, and not as rigid or regular as that found in standard database systems. Sometimes the structure exists but has to be extracted from the data. Sometimes also it exists but we prefer to ignore it for certain purposes such as browsing. We call here semi-structured data this data that is (from a particular viewpoint) neither raw data nor strictly typed, i.e., not table-oriented as in a relational model or sorted-graph as in object databases...

Semistructured data is not strictly typed like relational or object-oriented data and may be irregular or incomplete. It often arises in practice, e.g., when heterogeneous data sources are integrated or data is taken from the World Wide Web. Views over semistructured data can be used to filter the data and to restructure (or provide structure to) it. To achieve fast query response time, these views are often materialized. This paper studies incremental maintenance techniques for materialized views over semistructured data. We use the graph-based data model OEM and the query language Lorel, developed at Stanford, as the framework for our work. We propose a new algorithm that produces a set of queries that compute the changes to the view based upon a change to the source. We develop an analytic cost model and compare the cost of executing our incremental maintenance algorithm to that of recomputing the view. We show that for nearly all types of database updates, it is more efficient to a...

When a database is shared by many users, updates to the database schema are almost always prohibited because there is a risk of making existing application programs obsolete when they run against the modified schema. This paper addresses the problem by integrating schema evolution with view facilities. Each user is assigned his or her own database view, and develops application programs against the view. When new requirements necessitate schema updates for a particular user, then the user specifies schema changes to his personal view rather than to the shared base schema. Our view schema evolution approach then computes a new view schema that reflects the semantics of the desired schema change, and replaces the old view with the new one. This approach provides the means for schema change without affecting other views (and thus without affecting existing application programs). The persistent data is shared by different views of the schema, i.e. by both old as well as newly developed app...

We study the problem of maintaining materialized views of graph structured data. The base data consists of records containing identifiers of other records. The data could represent traditional objects (with methods, attributes, and a class hierarchy), but it could also represent a lower level data structure. We define simple views and materialized views for such graph structured data, analyzing options for representing record identity and references in the view. We develop incremental maintenance algorithms for these views, and discuss how to realize these algorithms when only a data warehouse (and not the data sources) knows the view definition. 1 Introduction Relational views are useful for controlling data access, specifying contents of caches (or remote copies), and other data management tasks. In this paper we study how to extend this view concept and the associated maintenance algorithms to what we call a graph structured database (GSDB). Informally, a GSDB is a collection of "o...

In this paper, we overview the Object-Protocol Model (OPM) and a suite of data management tools based on OPM. OPM is a data model that allows specifying database structures and queries in terms of objects and protocols specific to scientific (e.g., molecular biology laboratory) applications. Thus, scientific experiments and their resources can be described using OPM in a unified way. OPM data management tools provide facilities for specifying and querying relational databases in terms of OPM constructs, and automatically generate database specifications and queries for implementing OPM on top of commercial relational database management systems (DBMSs). OPM tools increase the efficiency of developing scientific databases using relational DBMSs, while insulating scientists from the underlying DBMSs. Key words: data management tools, object data model, scientific database 1. INTRODUCTION Keeping track and querying data generated by scientific experiments, simulations, and measurements re...

Personalized access and content syndication involving diverse conceptual representations of information resources are two of the key challenges of real-scale Semantic Web (SW) applications, such as eCommerce, e-Learning or e-Science portals. RDF/S represents nowadays the core SW language for creating and exchanging resource descriptions worldwide. Unfortunately, full-fledged view definition languages for the RDF/S data model are still missing. We propose RVL, a view definition language capable of creating not only virtual resource descriptions, but also virtual RDF/S schemas from (meta)classes, properties, as well as, resource descriptions available on the Semantic Web. RVL exploits the functional nature and type system of the RQL query language in order to navigate, filter and restructure complex RDF/S schema and resource description graphs.

The Semantic Web aims at easy integration and usage of content by building on a semi-structured data model where data semantics are explicitly specified through ontologies. However, ontologies and thereby ontology-based applications themselves suffer from heterogeneity. Therefore a new level of data independence is required to allow the customization of information, e.g. towards the needs of other agents, which can be achieved by exploiting database view principles. This paper addresses this issue and presents a new view mechanism for the data models underlying the Semantic Web, RDF and RDFS.

The construction and maintenance of data warehouses (views) in large-scale environments composed of numerous distributed information sources (ISs) such as the WWW has received great attention recently. Such environments are plagued with continuously changing information because ISs tend to continuously evolve by modifying not only their content but also their query capabilities and interface and by joining or leaving the environment at any time. In this paper, we outline our position on issues related to the challenging new problem of how to adapt views in such evolving environments. We first present a taxonomy of view adaptation problems by describing the dimensions along which view adaptation problems can be classified. Based on this taxonomy, we identify a new view adaptation problem for view evolution in the context of ISs capability changes, which we call View Synchronization. We also outline the Evolvable View Environment (EVE) that we propose as framework for solving the view sy...

View materialization is known to be a valuable technique for performance optimization in relational databases, and much work has been done addressing the problem of consistently maintaining relational views under update operations. However, little progress has been made thus far regarding the topic of view materialization in objectoriented databases (OODBs). In this paper, we demonstrate that there are several significant differences between the relational and object-oriented paradigms that can be exploited when addressing the object-oriented view materialization problem. We use the subsumption relationships between classes to identify branches of classes to which we do not need to propagate updates. Similarly, we use encapsulated interfaces combined with the fact that any unique database property is inherited from a single location to provide a "registration/notification" service for optimizing incremental view updates. We also report results from the experimental studies we have run ...

Object-oriented view mechanisms have received much attention in the literature in recent years, since they provide powerful mechanisms for addressing tasks such as customized tool interfacing to object-oriented databases (OODBs) and interoperability of heterogeneous databases. However, little progress has been made thus far on addressing the topic of view materialization in object-oriented databases. In the context of the MultiView project, we have developed an object model and an accompanying set of algorithms for the support of updatable materialized views in OODBs. We take advantage of unique features of the MultiView model, including its support for object-preserving queries, the integration of base and virtual classes into a unified and consistent global class hierarchy, and an object-slicing approach. In this paper, we present the MultiView model of materialized views, supporting updates on both base and virtual classes. We also describe a set of efficient algorithms for increm...