1 Meditech2011_L1801 Medical Services Optimization using Differential Evolution F.-C. Pop 1 , M. Cremene 1 , M.-F. Vaida 1 and A. Șerbănescu 2 1 Faculty of Electronics, Telecommunications and IT, The Technical University of Cluj-Napoca, Romania 2 The Faculty of Dental Medicine, "Iuliu Hațieganu" University of Medicine and Pharmacy, Cluj-Napoca, Romania Abstract—This paper proposes a method to compose and optimize medical services as business workflows. Such a work- flow consists in a set of abstract services, and for each abstract service there are several concrete services. Since each medical service has different QoS (Quality of Service) parameters such as response time, rating, distance and cost, determining the optimal combination of concrete services that realize the ab- stract services of the business workflow is an NP hard prob- lem. Recent proposals for solving NP optimization problems indicate the Genetic Algorithms (GA) as the best approach for complex workflows. But this problem usually needs to be solved at runtime, a task for which GA may be too slow. We propose a new approach, based on Differential Evolution (DE), that converges faster and it is more scalable and robust than the existing solutions based on Genetic Algorithms. Keywords— Services, Composition, QoS, Optimization, Se- lection, Genetic Algorithms, Differential Evolution I. INTRODUCTION A. Background The Service Oriented Architecture (SOA) model has be- come very popular in enterprise environments, where the complicated business logic is implemented by combining the functionality of various services. First, the business functions are defined. These functions represent the set of activities used to manage the assets of the organization in their various states. Then, the business functions are further decomposed into services, which implement the logic re- quired to realize defined functions. In software engineering, SOA defines how to discover and integrate disparate applications from different platforms into web-based applications. For example, one image pro- cessing application can be composed of several independent software components, each of them realizing a different function: enhancements, rotation, segmentation etc. and each of these components can be offered by a different service provider. Such a process that combines the func- tionality of multiple services is called service composition, and the resulted application is called a composite service. In medicine, a service provider could be, for instance, a dental office, which offers various dental treatment services. A composite medical service can then be defined as any medical activity that requires the patient to benefit from two or more different medical services. The patient (or the user of a service) is called a service consumer. A contract (formal or informal) is defined be- tween the service provider and the service consumer to specify the level of service. This contract is called the Ser- vice Level Agreement (SLA). For example, the SLA be- tween the dentist and the patient for a dental implant service may include the amount of time the implant is guaranteed to last, the cost of the medical procedure or the average rate of success. Such attributes represent the Quality of Service (QoS) properties of a service. Two services that provide the same functionality often have different QoS properties. For example, many clinics offer a similar range of medical tests, but promote different prices and require different amounts of time to deliver the results. One may be cheaper, but require longer time to provide the results than a more expensive service. B. Motivating example A composite service can be described as a process that involves the execution of several activities according to a workflow. An example workflow for a series of clinical tests is depicted in Fig. 1. This workflow consists of the following activities: S1. Assisted General Diagnosis for reading the pa- tient’s symptoms and classifying them in one of the 3 (example) categories: Heart Disease Symptoms, Digestive System Symptoms or Other Symptoms. According to the assigned category, the patient is then scheduled for specific medical tests. S2. Cholesterol Test for measuring the cholesterol lev- el, S3. Cardiac Exam for investigating signs of any cardi- ovascular pathology, S4. Endoscopy, where the digestive tract is investigat- ed, S5. Physician Consultation for having a physician ex- amine the patient’s symptoms and the results of the scheduled investigations, S6. Send Test Results that ensures the delivery of the patient’s investigations result to his home and/or the location of his medical records.