Assembling a coherent view of distributed heterogeneous information and information processing resources is a challenging and important process for inter-organizational collaboration and service provision. We refer to this process as information integration. However, traditional information integration approaches do not consider human intervention and exceptions, such as obtaining access approvals from service providers. Therefore, we propose a workflow-based approach to address this problem. This is particularly suitable in a loosely coupled and autonomous Web services environment. In this paper, we propose an implementation framework of workflow-based information integration (WII) comprise four layers, namely, application layer, workflow layer, service layer, and message layer. In particular, our paper focuses on the workflow layer from the aspects of control-flows, data-flows and exception-flows by using the business process execution language for Web services (BPEL4WS), extended with our proposed data-integration and exception-handling assertions. Each service provider provides Web services at the service layer and BPEL4WS orchestrates them together in order to achieve workflow-based information integration plans. The message layer comprises SOAP message specifications. We map information into SOAP messages and link the proposed exception-handling assertions in BPEL4WS to SOAP-fault implementations. Lastly, we demonstrate the feasibility of our approach with a practical health administrative information integration case study at the application layer and examine some typical use cases of exceptions.