Privacy, Continuity and Performance...

Of the "big four" non-functional aspects of a system: security, privacy, continuity and performance, typically privacy and security are viewed together; there is no doubt about their relationship.

The relationship between privacy (more generally information management) and continuity and performance is much more subtle. Certain decisions in these areas have an effect upon the information management aspects. Consider a piece of middleware that for both continuity and performance reasons

1. batches incoming data (for later processing or sending to some other system)
2. caches authentication data (for "fast(er)" login)

Both require data to be held for a certain period of time and data to be removed. There are also implications for the storage of that data in terms of whether it is secured through some means (eg: encrypted file system, database, fields...) and the internal processing and communication mechanisms.

We are primarily concerned with minimising the amount of data held and avoiding a single point of failure which would allow access to all the data. We have three basic options:

The monolithic system has potentially greater performance characteristics, but less so with regards to continuity and privacy - these latter two having a single point of failure. The facade while providing a single API decreases the performance but potentially facilitates better continuity through decoupling internally the authentication and data-handling and the decoupled system places much more responsibility onto the client for handling the correct calling sequences but better deals with privacy by reducing the amount of available data via any one API and component.

However as we decouple the system we increase the amount of inter-component communication and introduce a different set of information management and continuity issues, such as securing these data-flows and the leaky abstraction of network/communication failures.

The point here is not to provide a definitive answer of whether one solution is better than another but to emphasise the subtle interaction between privacy, continuity and performance in differing architectural solutions.