Querying Conflicting Web Data Sources

Over the last twenty years, information integration has received considerable efforts from both industry and academia. Approaches to information integration developed so far can be categorized as follows: (1) first-generation approaches, that require the definition of a global schema and a semantic integration which should be performed upfront (before query execution); (2) second-generation approaches, well illustrated by the

dataspace management

concept, which promote a

pay-asyou-go

data integration. The first category has led to well known mediation approaches such as GAV (Global as View), LAV (Local as View), GLAV (Generalized Local As View), BAV (Both As View), and BGLAV (BYU Global-Local-as-View). Approaches pertaining to the second category are geared towards the development of dataspace management systems and are currently gaining a lot of attention. In this chapter we are interested in exploiting both types of approaches in querying conflicting data spread over multiple web sources. To this aim, first we show how an XML-based BGLAV approach can handle these conflicting data sources, then we describe how the same problem can be addressed by using the Multi Fusion Approach (MFA), an approach pertaining to second-generation techniques. Both BGLAV and MFA are illustrated in using genomic data sources accessible through the Web.