Overview

Teaching: 0 min
Exercises: 0 min

Questions

• How do design principles differ for research software

Objectives

• To understand design constraints for research software

Research Software Specific Challenges

For most of research software we have a positive feedback loop. When we start exploring some phenomenon we devise a mathematical model for it. In the initial stages one typically focuses on one or two most accessible aspects of the problem. So one makes simplifying assumptions. As understanding grows one starts to relax the simplifying assumptions and the model grows more complex. A more complex problem will usually need more complex software and more hardware resources. The more complex problem will in turn lead to greater understanding … and thus the positive feedback loop persists.

This process leads to several challenges that are unique to RS

• Many parts of the model and software system can be under research
• Requirements change throughout the lifecycle as knowledge grows
• Real world is messy, it does not always yield to easy componentization
• Connectivity may become very complex
• Access to hardware resources may demand efficiency in computation that can be at odds with modularization

An addition challenge is faced by scientific software in that verification is complicated by floating point representation

SOLID Principles Pose Some Difficulties

As shown in the figure, some of the SOLID principles do not work too well with RS. For example the Single Responsibility princple can become difficult to follow when there is a lot of lateral interaction become components and computational efficiency demands fusion of operations. In general greater understanding tends to lead to tighter coupling among components. Open/closed principle run into problem when new insights need invasive alteration of either the numerical method or specific implementation details. To avoid unnecessary code duplication it may be best to allow modification in the existing code. Lateral interactions and tight coupling among interfaces can often make it difficult to segregate interfaces, or to avoid dependency inversion.

We will see examples of some of these challengs that we work through in the next section

Additional Considerations for Research Software

Some additional considerations come into play for designing RS that may not be needed for enterprise software. These are:

• Many RS projects have interdisciplinary teams, and many different types of expertise are needed to put together the whole software. It is not possible for all the team members to know all aspects of software development. Some understanding of everything is necessary for needed interactions, but in-depth knowledge of everything is simply not possible. Therefore, the design should permit separation of concerns. For example, in a multiphysics simulation software the design should be such that the domain scientists can focus on their specific physics model and its descretization, applied mathematicians can focus on details of numerical methods and the performance engineers can work on optimization.

• In an earlier section about phases of design we had mentioned “types” of components and binning them. A base framework that acts as the substrate on which capabilities can grow is important for most RS. Therefore, one should differentiate between components that need to provide that stability, such as the discretization models, I/O, book-keeping, and other infrastructural support, and those that provide the needed capabilities such as physics models. The number of initial interations of the three design phases differ for the different component types. The former should be near final in design before the latter begin to be embedded in the code. The physics components should follow agile methodology much more diligently, and be nimble to be able to incorporate new discoveries in the code rapidly.

• During design thought should be given to extensibility build into the framework and in other components.

Key Points

• Design principles need to be adapted for research software