In the context of large-scale distributed component-based systems, this article motivates the need for and defines a general open query service. This query service allows for retrieving and selecting components from both repositories and deployed running systems. The problem of retrieving components from repositories has already been tackled by many research works whose purpose is to construct systems by assembling reusable components, typically in the context of COTS components. However, the proposed query services allows for an uniform efficient associative access to both repositories and running systems, while beeing based on distributed database techniques, which is the main contribution in this paper.