Top-level architecture is a high-level, system-wide, all-encompassing architecture that describes the top-level components in the system. Depending on the requirements, this architecture might detail certain things such as communications methods, distribution of components, platform types, technology types, and so on.
Low-level architecture is a high-level description of a subsystem or a part of a larger system. Low-level architecture should describe external interfaces, internal components, and other aspects that describe how certain requirements are fulfilled.
Impedance Mismatch came out of the Object-Relational Mapping (ORM) movement, and attempts to describe the inherent disparity between what a relational database can model and what an OO language can model. This type of mismatch occurs outside the relational databases and can rear its head anywhere two different types of systems integrate.
Decoupling is the process of reducing dependencies, or changing the type of dependencies...