Opaque Boxes

The idea is to create an opaque box. You can use it to do a few well-specified things, but you need to stay within its tolerances.

The box has some finite set of entry-points. One or more points may allow some dynamic behavior or statefulness as represented by a question and answer paradigm.

If the box can do X, there is a way of testing whether X has been done, or not. 

If the box provides optimized methods, any and all of the information needed for those optimizations is entirely constrained to being in the box and is not available on the outside. If there is a means of toggling the optimization, then there is a way to see that it is set or not.

If the box stores data for later use, the outside format is RAW and it is converted to something else once inside the box. There is a means of getting the RAW data back as it was specified. If there is some other useful internal format, there might be a way of returning that directly, but only if that format itself does not explicitly depend on any of the ‘code’ in the box. So, its more likely that if the box doesn’t implement an external standard, then to get back FORMATTED data requires the box to format it on the way out. 

A simple box equates to the computational model of a Turing Machine (TM). That is, it is just 1 computational engine, from the outside perspective. It takes some input, runs a computation, and produces some output. It is deterministic and will always produce the same output with the same input. 

The communication between the calling program and the box may or may not be asynchronous, but if it is the latter, then there is a means of binding together different entry-points into the same operation (they all happen or they all fail, there is no in-between). 

A non-deterministic box is a simple box where the output can or is guaranteed to change, even though the inputs are consistent. 

A composite box is one that encapsulates the interaction between many TMs. So a request, whether it is read-only or a write, is bound to the behavior of a set of different computational engines, that should be assumed to be asynchronous. If there are multiple TMs, but they are sitting on a synchronous bus, we still shouldn’t consider them as just a single TM. 

A composite box may or may not preserve order. It may or may not protect interdependencies. The onus then is on the user to ensure that a composite box is only used under reasonable circumstances, where independence is either easily provable or where each and every dependence is guaranteed by known properties of the specific box.

A simple box, subject to underlying resource partitioning, will usually return results within a fixed range of time. There is a potential for the halting problem to kick in, so it could possibly never return. On top of this, a composite box may also wait forever on the results of an underlying asynchronous communication, so some of its properties may require it to pause operations and eventually run out of any queuing, so there is a flow problem on top as well. The caller of either box needs to set a bound for the operation and to react appropriately when the box is indisposed. This is different from being unavailable.

A composite box can be built around a collection of other simple and composite boxes. If any of those boxes is asynchronous or non-deterministic, the outer box picks up those properties, unless something has been explicitly done to negate them.

It is possible to frame any one-time or continuous computations in terms of boxes. It is complete. In decomposing the problem this way, the attributes of the boxes have to be explicit and understood so that anything built on top needs to handle the communications with care. While this perspective is somewhat abstract, it is also formal enough that it can be used as the structural guidelines for a larger architecture. That is, we could decompose a very large system into a great number of boxes that could cover 100% of the code. If the boxes work properly and all of the attributes are explicitly handled, then the system works properly.