Web Services (WS) technology is failing in providing service-discovering techniques considering non-functional properties. Semantic search is based on functionality, regardless of non-functional requirements. Quality properties of services are considered marginally; definitions and metrics are not provided, making difficult common understanding and retrieval of concepts. Using quality standards is made difficult due to conceptual inconsistencies among different standards. This work proposes an ontological WS discovery approach based on semantic matching process of functional and non-functional requirements. A WS is considered a software component providing functionality accomplishing specific quality goals. Our WS discovery process matches functional and non-functional requirements, ranks according to preferences, considering three related ontologies: 1. An ontology to integrate quality standards and retrieve properties and metrics, 2. An ontology to model relations between these standards and preferences to rank functionality and/or qualities, 3. An ontology relating quality models to WS functionality. A prototype tool supports this approach.