Manufacturing supplier discovery in virtual environments is a computationally intensive task. Existing electronic marketplaces for manufacturing services, due to their syntactic and human-oriented approach in search, fail to build accurate connection between seller and buyers. Automation and intelligence are the two key requirements of web-based solution for efficient deployment of virtual supply chains. It was previously shown that an ontological approach, because of its semantic nature, yields more precise results compared to traditional techniques such as keyword search. While the proposed ontology, known as Manufacturing Service Description Language (MSDL), can sufficiently encode structural knowledge in the manufacturing domain, it doesn’t have the required level of expressivity for representing constraint knowledge. This paper introduces an extension to MSDL for formal representation of constraints and rules based on Semantic Web Rule Language (SWRL). To identify the rules and to evaluate the performance of the rule-based technique, an experimental approach is followed in this research.