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"
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.
DeRemor and Kron have this to say about programming in the large vs in the small (taken from the abstract of their paper - see the references section, below):
"By large programs we mean systems consisting of many small programs (modules), possibly written by different people. We need languages for programming-in-the-small, i.e. languages not unlike the common programming languages of today, for writing modules. We also need a “module interconnection language” for knitting those modules together into an integrated whole and for providing an overview that formally records the intent of the programmer(s) and that can be checked for consistency by a compiler. We explore the software reliability aspects of such an interconnection language. Emphasis is placed on facilities for information hiding and for defining layers of virtual machines."
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