Schema integration is the process by which schemata from heterogeneous databases are conceptually integrated into a single cohesive schema. In this work we propose a modeling framework for schema integration, capturing the inherent uncertainty accompanying the integration process. The model utilizes a fuzzy framework to express a confidence measure, associated with the outcome of a schema integration process. In this paper we provide a systematic analysis of the process properties and establish a criterion for evaluating the quality of matching algorithms, which map attributes among heterogeneous schemata.