A Dual-Mode Retrieval-Augmented Generation System for Interactive Question Answering of Public Tender Documents

This paper presents a Retrieval-Augmented Generation (RAG) system for question answering over the set of documents of a public tender. The proof-of-concept chatbot is intended to provide support to officers participating in the evaluation process of a tender whose documents are indexed. The system implements a dual-mode retrieval strategy —supporting both semantic and lexical search— to extract relevant context and uses an instruction-following language model to generate grounded responses based strictly on the retrieved information. The system is designed to assist officers in exploring tenders, evaluation reports, and award justifications through natural language queries. In order to assess the system, the documents of a tender have been generated symtheticly. Qualitative testing demonstrated that the system provided accurate, verifiable answers, avoiding unsupported inferences. The architecture emphasizes document fidelity, interpretability, and usability for non-technical users involved in procurement oversight. Future work may extend the framework to support the identification of fraud-related patterns.