Today, the deployment of Web services in many enterprise applications has gained much attention. Service network inhibits certain common properties as they arise spontaneously and are subject to high fluctuation. The objective of consumer is to compose services for stable business processes in coherence with their legacy system capabilities and with better quality of services. For this purpose we have proposed a dynamic decision model that integrates several performance metrics and attributes to monitor the performance of service oriented systems in order to ensure their sustainability. Based on the available metrics, we have identified performance metrics criteria and classified into categories like time based QoS, size based QoS, combined QoS and estimated attributes. Then we have designed service network monitoring ontology (SNM). Our decision model will take user query and SNM as input, measures the performance capabilities and suggests some new performance configurations like selected service is not available, physical resource is not available and no maintenance will be available for the selected service for composition.