The web explosion, both at internet and intranet level, has transformed the electronic information systemfrom single isolated node to an entry points into a worldwide network of information exchange and businesstransactions. Business and commerce has taken the opportunity of the new technologies to define the ecommerceactivity. Therefore one of the main challenges for the designers of the e-commerceinfrastructures is the information sharing, retrieving data located in different sources thus obtaining anintegrated view to overcome any contradiction or redundancy. Virtual Catalogs synthesize this approach asthey are conceived as instruments to dynamically retrieve information from multiple catalogs and presentproduct data in a unified manner, without directly storing product data from catalogs. Customers, instead ofhaving to interact with multiple heterogeneous catalogs, can interact in a uniform way with a virtual catalog.In this paper we propose a designer support tool, called SI-Designer, for information integration developedwithin the MOMIS project. The MOMIS project (Mediator environment for Multiple Information Sources)aims to integrate data from structured and semi-structured data sources.