This research concerns the definition of a service-oriented approach for business processes modeling. Business services are reusable process units that contain one or several process fragments for satisfying business goals. Business services may be composed in various manners to satisfy business process designer's needs. A goal-oriented business service model supports business knowledge representation for specifying and composing business services. Ontologies for business systems domain provide a common vocabulary for matching business process designer's request and available business services. A service composition process organizes the discovery, the selection and the assembly of business services to dynamically build business processes tailored to business designer's requirements.