Software development project size and methodology

Here is a short description of software development characteristics for projects of different size and its impact for methodology.

Very simple application (single programmer, tester - one man for all)

Requirements are simple and all known. If you are writing very simple application, using good architecture plan and code writing practices, as a result you should have clean ready to change application. Adding automated tests makes changes easier without software quality drop. You know all details without looking into documentation, and testing new changes and features during implementation. All changes go to the code repository with comments and TODO file.

Simple/medium, application (team of 1+ programmers and other stakeholders)

The requirements should be gathered and agreed before development. You are using some kind of Issue Management System, tracing all change requests. Application is divided into main modules referred in task details. Programmers know what to change and what are dependencies between modules and side effects of implemented changes. Testers know main modules, and are going through test procedures of modules and functionalities. Procedures are short and clean and there is a natural place for agile methodologies.

Large application, (team of 10+ programmers and stakeholders)

Application is quite huge. Preparing requirements is often separate project. Every change request is thoroughly reviewed then approved. Application have many interdependencies caused by re-usability and connection points. Some changes have strictly local effects for given feature, those are less harmful. Other change some lower level service, probably unit tested, but still having impact on bigger process. Automated tests are not covering every possible use of code, manual top level functional tests are last line of defense in quality assurance. In real life every module has many connections with other modules. Testers have very limited knowledge about those dependencies. Everyone needs more plans, documents, procedures and artifacts that is slowing down the whole process. Practical solution is to divide the large project into smaller, less complex sub-projects.

At this level of complexity there are many "process complete" management methodologies. The winning one is the best suitable for given project, reducing risks and allowing to finish project at planned costs and time.