already been a valuable tool for ease of integration is another factor to be looked into for reducing operational costs. When the business and technical requirements change, the infrastructure should be flexible enough to adopt the changes. The faster the resources can adopt a change in requirements the more rapid will be the time to market. This means significant reduction in the service development and delivery time. The adoption of lean prac- tices should be done without compromise in service quality. The OSS architecture has migrated over the years from legacy to loosely coupled and finally to a distributed model (see Figure 21.1). Legacy systems were inflexible to change and were poorly integrated. There was minimal or no distribution of data. This changed in a loosely coupled system where service did interoperate but there existed multiple databases and user interfaces. The NGOSS approach is for a distributed environment as advocated in SOA, where interfaces are published and there is a seamless flow of information between modules, which are policy enabled. 21.3 NGOSS Lifecycle There are a number of techniques for developing and managing software projects. Most of them deal with either the management of software development projects or methods for developing specific software implementations including testing and maintenance. Some of the most popular frameworks currently used are the Zachman Framework, Reference Model for Open Distributed Programming (RM-ODP), Model Driven Architecture (MDA), and Unified Software Development Process (USDP). Most of these techniques look into a complete life cycle of software Fundamentals of EMS, NMS and OSS/BSS development from specification of business requirements to deployment of the software. NGOSS tries to incorporate best practices from these techniques and tries to streamline the life cycle to telecom industry. Some of the important concepts from the existing techniques that were incor- porated in NGOSS lifecycle and methodology are: Model based development as in MDA