Most quality management systems (QMS) which integrate software development are based on a single software development method. This particular method is enforced on all projects. The resulting QMS has to fulfil the ISO 9000 standards  and enables the control of the projects and the improvement of the development process, supporting it with all necessary guidelines and providing one terminology for the whole company. However, using only one specific method is not necessarily the best solution for a company with very heterogeneous projects and products. Requirements of customers, existing experience and training in the teams, projects still using structured methods and newer ones using object-oriented methods, adaptation of methods for special circumstances, and evolving modelling techniques, all of these factors call for the coexistence of different modelling methods within one company. If a QMS is based on only a single method, many projects might run outside the quality management regulations, unless the QMS excludes the details of the software development process.
This problem can be overcome by the use of model architectures and model architecture frames. A model architecture describes the models that are developed within one specific method or project. All the different model architectures are derived from the generic model architecture frame. Such a frame, and not just one specific method, becomes the basis for the company wide regulations.
This paper describes reasons for having multiple methods and life cycle models within one QMS, explains the basic concepts of defining a QMS using model architectures and model architecture frames, and shows how this approach may be applied in a project.