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Software Fortresses: Modeling Enterprise Architectures Review by Charles Ashbacher
An analogy that is understandable in practice and transference
A software fortress is a model for a conglomerate of software systems serving a common purpose. The systems work together very closely in a trust relationship to provide functionality to a world generally considered hostile. An enterprise system is then built from a collection of different fortresses where each one performs a different function. This model makes sense, in that there are those you trust and those you don't. Since a trust relationship requires more effort to maintain than one without trust, extraneous trust relationships are inefficient. Communication between fortresses can then be done using secure channels and trust relationships can be established by appropriate verifications between parties or by a trusted third party fortress.
The ways in which two fortresses will work together are defined by formal agreements between them known as treaties. Channels through which fortresses communicate are known as drawbridges, using the castle, moat and drawbridge analogy. This is also a good one, as it is much easier to monitor communication when there are few channels that are easily controlled.
I found the models to be very understandable, managers trying to get a handle on the general aspects of security in an enterprise will have no difficulty in applying the fortress analogies to their software enterprises. At first it would seem that the fortress model leads to a decrease in security, but that is a false supposition. By isolating and restricting the security to where it really needs to be, it is easier to make it sound.
To be effective, an analogy must be understandable by itself and be transferable to the situation it describes in a way where the transference is also understandable. The software fortress analogies satisfy both conditions, everyone understands the concept of a castle with walls, a moat and drawbridges for access. Everyone inside trusts the other, and those outside the walls are generally considered dangerous. It is also transferable in an understandable way, which makes it suitable for the creation of an architectural view of a large software system.