Programming in the large and programming in the small

In software engineering, programming in the large and programming in the small describe two different approaches to writing software. The terms were coined by Frank DeRemer and Hans Kron in their 1975 paper "Programming-in-the-large versus programming-in-the-small" A similar, later distinction is Ousterhout's dichotomy between system programming languages (for components) and scripting languages for glue code, connecting components.

Fred Brooks identifies that the way an individual program is created is different from how a programming systems product is created. The former likely does one relatively simple task well. It is probably coded by a single engineer, is complete in itself, and is ready to run on the system on which it was developed. The programming activity was probably fairly short-lived as simple tasks are quick and easy to complete. This is the endeavor that DeRemer and Kron describe as programming in the small.

Compare with the activities associated with a programming systems project, again as identified by Brooks. Such a project is typified by medium-sized or large industrial teams working on the project for many months to several years. The project is likely to be split up into several or hundreds of separate modules which individually are of a similar complexity to the individual programs described above. However, each module will define an interface to its surrounding modules.

Brooks describes how programming systems projects are typically run as formal projects that follow industry best practices and will comprise testing, documentation and ongoing maintenance activities as well as activities to ensure that the product is generalized to work in different scenarios including on systems other than the development systems on which it was created.

In software development, programming in the large can involve programming by larger groups of people or by smaller groups over longer time periods. Either of these conditions will result in large, and hence complicated, programs that can be challenging for maintainers to understand.

With programming in the large, coding managers place emphasis on partitioning work into modules with precisely-specified interactions. This requires careful planning and careful documentation.

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