Bulder.com 020923 MEASURE THE QUALITY OF WEB SERVICES As a developer of Web services, you should understand what quality indicators customers look for. Even if you are not developing commercial Web services, you may still have internal users that depend on the quality of your applications. For many organizations, the metrics expressed by quality of service (QoS) statements is a major factor in choosing Web services vendors. MEASUREMENT The basic element of QoS in any organization is measurement. Based on measurement histories, QoS metrics inform customers about the quality of your Web services. Here's a short list of metrics that you might use to describe your Web services: * Accessibility: How reliable is access to the service? * Accuracy: How many errors does the service produce over a period of time? * Availability: How often is the service unavailable? * Capacity: How many concurrent connections does the service support? * Completeness: How many of the specified features are currently available? * Fault tolerance: What kinds of failures can the service tolerate? * Integrity: How does the service respond to transactional failures? * Latency: What kind of response time is expected on a single request? * Performance: What kind of response time is expected on volume requests? * Regulatory: How aligned is the service with appropriate regulations? * Reliability: In aggregate, how reliable is the service's access and availability? * Security: How does the service authenticate and authorize users, and encrypt data? * Standards: How much does the service adhere to applicable standards? * Usability: Considering an aggregate of all metrics, how usable is the service? QoS METRICS FOR WEB SERVICES Web service providers should also be particularly concerned with QoS metrics. Measuring various aspects of your services and publishing statistical summaries will provide metrics to your customers. Depending on the service, you may focus on different metrics. Understanding the competitions' QoS metrics can also help in developing a competitive advantage. Because Web services are built on new technologies and often use public Internet infrastructure, they're prone to failures. By measuring various facets of your application quality, not only can you provide valuable metrics to your customers, but you can also keep your services running at peak performance. SERVICE LEVEL AGREEMENTS QoS metrics aren't very useful without a service level agreement (SLA). SLAs provide a negotiated agreement and contract between service providers and users. In general, the SLA guarantees metrics within a certain range and includes compensation provisions for when the metrics fall out of that range. The important thing to remember is that without an SLA, QoS metrics are almost meaningless to your customers. If you're using your metrics to not only keep yourself in check, but also to gain a competitive advantage, then having an agreement with your customers to meet specific QoS criteria can go a long way toward bringing in business. As a Web service provider, you're constantly changing--you're adding new hardware, switching network providers, building new services, replacing old services, and so on. Each change can dramatically affect your published metrics. It's important to keep your customer SLAs up to date and make addendums to them as your services evolve. Brian Schaffner is a senior consultant for Fujitsu Consulting. He provides architecture, design, and development support for Fujitsu's Telcom360 group.