Software Architect's Handbook

Scope of modifications

Not all changes to software are equal, and the scope of a particular modification is a factor in how difficult the change will be to implement. The larger and the more complex the modification, the greater the effort to complete it.

In addition to size, if the changes require architecture level changes, that will increase the level and scale of effort involved. Some components and their interactions may need to be refactored extensively for large changes.