7. Frameworks#

Frameworks provide a collection of reusable building blocks that solve recurrent problems in specialized domains (e.g., control systems, distributed services, data processing, hardware interfaces) and facilitate developing observatory applications. At the same time, they provide an isolation mechanism from underlying software layers. The use of these component frameworks is key to building a cost effective system [Youn10] and provides the following benefits:

  • Improved internal reuse. The design of the component frameworks is based on set of recurrent design patterns [Gamm94] (e.g., Controller, Pipeline, Panel, Workflow, Sequence, Wrapper). A set of base classes implements these design patterns by means of composition/delegation or specialization.

  • Improved consistency of designs and compliance with standards.

  • Improved robustness. Components that are reused in multiple scenarios and different Subsystems are tested in more diverse conditions.

  • Reduced maintenance cost, since knowing about fewer types of Components is required.

  • Improved external reuse. Component frameworks implement wrappers for external software packages. Wrappers help reduce dependencies between subsystem implementation code and external software packages and minimize the propagation of changes through interfaces.

Frameworks have key distinguishing features compared to normal libraries:

  • Inversion of control. In a framework, unlike libraries or normal user applications, the overall program’s flow of control is not dictated by the caller, but by the framework.

  • Extensibility. A framework can be extended by the user usually by selective overriding or specialized by user code to provide specific functionality.

  • Non-modifiable framework code. The framework code, in general, should not be modified, except regarding extensibility. Users can extend the framework, but cannot change its code.

This section presents the design of the GMT common frameworks, from the domain engineering process to identify common building blocks, to the design and intended usage of each individual framework.