Migrating towards Service Oriented Architecture SOA has become a major topic of interest during the recent years. Since emerging service technologies have forced non-service based software systems to become legacy, many efforts and researches have been carried out to enable these legacy systems to survive. In this context, several service identification solutions have been proposed. These approaches are either manual, thus considered expensive, or rely on ad-hoc criteria that fail to identify relevant services. In this paper, within the big picture of migrating object-oriented legacy systems towards SOA, we address automatic service identification from source code based on service quality characteristics. To achieve this, we propose a quality measurement model where characteristics of services are refined to measurable metrics.