A MODAF Architecture Description Only Applies to a ‘System of Systems’?

In the MODAF metamodel (M3) v 1.2.004 we have:

ArchitecturalDescription : public <<stereotype>> class

A specification of a system of systems at a technical level which also provides the business context for the system of systems.

This definition of an architecture description has been unchanged since at least v 1.1 (May 2007).

This defines an AD as a specification. This is too restrictive and doesn’t fit current usage within the MoD since MODAF ADs are more often used to discover and analyse the architecture that exists in order to assess the impact of decisions or proposed design changes.

The real problem is the ‘system of systems’ bit because it looks to be misusing the term. In restricting an AD to a ‘system of systems’ and not ‘system’:

 
• Are they then saying it is only an AD when it describes a ‘system of systems’? Since a ‘system of systems’ is formed from systems that have an independent existance this definition means that you can’t have a MODAF AD of a submarine where the systems are tightly coupled and have no meaningful existence away from the submarine.
 
• Are they saying MODAF cannot be used to describe a vanilla system? This states that a description of the architecture of a system (formed from essential parts that aren’t themselves systems) isn’t an AD.
 
• Are they saying that ‘system of systems’ is a new type (in which case how do they know it can be described using MODAF)? This would be technically incorrect since a ‘system of systems’ is of the type ‘system’ with the emergence et al that this brings.

I don’t for one minute believe that any of this is the intent nor that this represents how MODAF ADs are intended to be used. It doesn’t therefore reflect the real use of an AD and needs to be changed to make it a valid definition.

The good thing is that the MODAF M3 recognises the distinction between the architecture (of the system) and the thing that describes it (the AD). Far too many others confuse the 2 concepts

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External Links

• MODAF Metamodel (M3)

Representing ‘The Needy’ in MODAF - The Needline

I’m spending a lot of time playing ‘spot the difference’ to capture the changes in the Canadian DNDAF (at v1.7 from 1.6), MODAF (at 1.2.004 from 1.2.003) and NATO AF (at 3.1 from 3 - or at least will be when the documentation is properly accessible). This is harder than it needs be owing to the patchy nature in which changes are identified and recorded in the various architecture frameworks - or not. In this respect MODAF is definitely one of the better frameworks.

One of the significant changes with the release of the MODAF 1.2.004 (May 2010) is that all resources are now equal in that not only can interactions (Resource Interactions) be identified between them but can also be characterised and flows of information, energy, materiel and people captured. Prior to this MODAF could only characterise interactions for artefacts, systems but not for human resources. 1.2.004 also  adds the ability to show materiel, energy and people flows to various systems and operational views.

All of this is good and much needed for describing the real world. It does now highlight the Needline as a throwback to the earlier information-only days. In the solution-free operational views the node (the nearest we get to ‘thing’ or ‘stuff’ ) is connected to another node by a needline. In 1.2.004 it is defined as:

A relationship between Nodes representing a bundle of InformationExchanges.

i.e. a collection of information exchanges.

In the old days (MODAF 1.1 - May 2007) it was defined as:

A relationship specifying the need to exchange information between nodes…

which has a more explicit (=better) link to it being a line identifying a need and hence the name of the stereotype.

The current definition is a poor one since it defines Needline only in terms of the MODAF metamodel itself. Stereotypes are supposed to represent something in the real world and therefore the ones that can be selected by an architect should be defined in terms of the parts of the real world that they are supposed to represent. The new definition contains nothing in terms of representation or the real world equivalent. It’s almost as if the purpose or point of having it have been lost as there’s no sense of a Needline being used to represent a need for an exchange (of some type) any more - this has been thrown away.

It still doesn’t seem right to only being able to express a need for information. Why not a need for energy, people or materiel? It would make much more sense to unify any need under needline and define it as A relationship identifying the need to exchange energy, information, materiel or people. At least then it would be consistent with the rationalisation / equal treatment of resources (Resource Type). The resulting representation of exchanges is therefore inconsistent and it feels like the new exchange types have been tacked onto rather than incorporated within the metamodel.

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External Links

• MODAF Metamodel v1.2.004
• MODAF 1.2.004 Change Record
• MODAF Metamodel Version 1.1 Final 18th May 2007.