The new paradigm for distributed computing over the Internet is that of Web services (WSs). One of the key ideas of this new paradigm is the ability to create value-added Service-Based Applications (SBAs) by composing pre-existing services. Building SBAs necessitates the discovery and the selection of the most appropriate WSs that fit closely users' functional and non-functional requirements. Due to the large number of WSs that are advertised over public and private registries and the various functional and non-functional capabilities that are required by users, discovery and selection of WSs have become a real challenge nowadays. In this paper, we present a WS composition approach that is built upon both perspectives: intentional and operational. In the intentional perspective, we propose to model users' requirements for SBAs using the MAP formalism and specify the required WSs using an Intentional Service Model (ISM). In the operational perspective, we propose to discover the required WSs by querying the service search engine Service-Finder and select the most appropriate WSs by using many-valued concept lattices. To validate our approach, we use an analytical technique that is the monitoring to verify that the selected WSs assure the required users' non-functional capabilities.