Intent

The Time Inversion pattern is used to model dynamic collaborative behaviour between model components. To choose which responsibilities should be endowed upon a component, the modeller considers a goal that should be reached by one or more key components. This goal should be the end-goal. Reasoning backward from this end-goal the modellers searches for other components to delegate behaviour to, but in an inverted time frame: the first modelled object implements the last step in reaching the goal, the second the last step before that, and so on. The choice of candidate objects is from a list of active objects obtained from the  Active/Passive pattern.

Also Known As

• Demand-chain
• Pull model (Toyota)
• Just-In-Time

This article attempts to describe a possible implementation of an architecture process in organisations that strive towards greater agility.

The RACI matrix

Before diving into the architecture process itself, we think about roles and responsibilities in organisations. For this we often employ a matrix that we find helpful: the RACI matrix.

The matrix as shown above shows a possible situation for a specific project or organisational unit. We see that Smith is Responsible, Jackson is Accountable, and some others who are Consulted or Informed.

Various variations on this basic model exist, for more information see the links below this article.

What is the meaning of these terms?

• Responsible - means a person or role with the skills and or expertise to understand and explain, and to peers (other Responsible persons or roles) defend a specific policy or action
• Accountable - means a person or role with the assigned final right to decide, with the mandate and usually the funding to start or stop a certain organisational activity such as a project. Equivalent to an executive responsibility.
• Consulted - means a person or role that is consulted for the activity, because their input is necessary or desirable. The input is in the area of knowledge, skills or expertise, rarely on the executive level.
• Informed - means a person or role who should be informed of the proceedings or decisions taken, but is not directly involved in the process.

We focus in this article on the first two roles, because they are the most interesting with respect to the architecture process. Also we try to give a deeper meaning to the Responsible role, since we think that role has been undervalued in the literature, and we link this role to that of the architect.

xM

Exploratory Modelling is acronym-ed as xM, and the parallel with xP (eXtreme Programming) is not accidental: in a highly interactive development environment this modelling approach does for modelling what xP does for programming: it does away with procedures, documentation, or any activity that does not directly and visibly contribute to the end result. Moreover it cannot properly be categorised as modelling since the end result or deliverable of the xM effort is a running, executable software program. However, for the purpose of categorisation, but especially regarding the place of xM in the solution-realisation cycle, it can best be categorised as a modelling activity.

Abstract

This article describes an approach to modelling that is relatively unknown^[i] . It capitalises on capabilities of modern programming tools and languages, especially dynamic qualities, as well as advances in object-oriented modelling.

It empowers the development of DSL's, using what might be called a meta-DSL approach.

For the examples in this chapter (as in most of our projects) we have used a Smalltalk development environment, VisualWorks^[ii]  in particular, but the approach is in no way exclusive to the Smalltalk language or environment. The author and his colleagues at Sogyo have also applied the approach in a Microsoft VisualStudio environment with C# with comparable success. The approach is called eXploratory Modelling. Its aim is to significantly improve the modelling and requirements effort.

We will start by describing the overall xM process and an example xM session. This will hopefully convey the “feel” of xM. After this we will introduce several relevant theoretical issues intended as a first attempt at laying a foundation for xM practices.