The Web is a distributed environment rich with Web services going through continual metamorphosis. thus, sustaining semantic stability of service composition has become a major challenge. Automatic service composition enabled both by the use of ontologies that describe service domains and by user-specified constraints bound to the ontologies provides us candidate service pipelines at composition design time. The ontology-based languages for semantically describing web services, such as OWL-S, have been widely used. Though rich and comprehensive in their expressiveness, the use of these languages still leaves much of composition process manual. In this work, we present an ontology-based semantic web service composition system called OntoPipeliner. It employs a novel way of utilizing characteristics of Web services that reflect the classes and properties of domain ontologies and provides the ontology-guided constraints for automatic composition of services, in order to guide the user toward the best pipeline that meets the user requirements.