Theoretical considerations

The theoretical part describes abstractly the method with its steps that is used to iden-tify the frame structure. The practical application of these considerations take place in section 3.2.4. Like previously stated the method both for the theoretical and practical part will consist of two parts, a Top Down (3.2.3.1) and Bottom Up Approach (3.2.3.2).

3.2.3.1. Top Down Approach

Focus of the Top Down part is a literature analysis. Its goal is to identify a suitable the-oretical architecture model that can be used to cover both thelevelsandlayersaspect as it was previously described (3.2.1). Therefore, in a selection process suitable theoretical architecture models are identified. (A schematic graphical sketch of the process and its individual steps is provided in Figure 3.3.) The selection is twofold – first architecture models that cover full system descriptions (enterprise architectures) and provide a meth-odology to describe an overall architecture are extracted (Selection Process I in Figure 3.3).

In a second step it is evaluated how much those architecture models already cover C-ITS specific characteristics (Selection Process II in Figure 3.3). For both selection steps suitable criteria are identified in the theoretical part.

Figure 3.3.: Graphical representation of Top Down architecture model selection process.

In detail, the following steps will be executed:

Step 1: Identify theoretical architecture models

Step 2: Identify the requirements to select for criteria ’enterprise’ and ’method(ology)’, define selection process and criteria, undertake the selection

Result: selected architecture model(s)

Step 3: Identify the requirements to select for ’C-ITS’, define selection process and criteria, undertake the selection

Result: selected architecture model(s),

Step 4: Derive levels and layers from selected architecture models and denominate mis-sing parts based on C-ITS selection process

3.2.3.1.1. Step 1 – Identify theoretical architecture models

Searching for Enterprise Architecture models leads to a large number of potential can-didates. Numerous experts published books with descriptions about existing enterprise architecture models and their view on what are the best ones. This already shows the importance of the following step that focuses on the selection of suitable models and the need to clearly define strict selection criteria to significantly reduce the number of discus-sed models. Step 1 compiles an overview of existing architecture models.

3.2.3.1.2. Step 2 – Evaluation and selection process I

The first selection process is supposed to identify those candidates that actually provide an enterprise architecture methodology. For the evaluation, the two terms (’enterprise’ and

’methodology’) and their scope are defined. The selected definitions are used to derive the evaluation criteria and requirements for the subsequent selection process, details are described in Appendix A.1. For each candidate the strengths and weaknesses with respect to the identified evaluation criteria are fleshed out. The candidates, which are in line with the scope of the definitions, are selected for the second part of the selection process.

3.2.3.1.3. Step 3 – Selection process II

The candidates selected in the previous step are taken and are now analyzed with focus on C-ITS. Therefore, first C-ITS is characterized and the requirements and criteria are derived like in the previous step, details are described in Appendix A.2.

The Selection Process II then takes the characteristics of C-ITS and the criteria without a specific reference to C-ITS or enterprise architecture models and analyses how the single candidates selected in the previous step fulfill those criteria and characteristics. Again, this evaluation is done through an analysis of strengths and weaknesses for these specific characteristics. The candidate that best fulfills the requirements is finally selected.

3.2.3.1.4. Step 4 – Derive levels and layers from selected architecture models

The finally selected candidate(s) is (are) used to identify which levels and layers are used – these results will serve as input for the description of the frame structure. It is assumed that none of the available candidates is able to completely implement all the characteristics and criteria. Therefore, this step additionally identifies missing parts based on the C-ITS selection process. These aspects are detailed in the second part of the approach (section 3.3) and are required for a complete description of the abstract architecture.

3.2.3.2. Bottom Up Approach

Focus of the bottom up part is an analysis of already existing ITS and C-ITS architectures.

The goal is to identify the requirements from existing architectures in terms oflevelsand layersthat need to be covered in a future frame structure. This is done in a multi-stage process.

In detail, the following steps will be executed:

Step 1: Identify existing definitions of levels and layers

Step 2: Identify candidates of existing ITS and if available C-ITS architectures Step 3 Analyze candidates with regard to their frame structure

Step 4: Derive levels and layers from existing ITS and C-ITS architectures 3.2.3.2.1. Step 1 – Identify existing definitions of levels and layers

There are already papers available that analyzed and / or summarize the frame structures used in existing ITS architectures. Partially, they include abstract and general definitions as well as frame structure descriptions. This step collects the existing definitions and de-scriptions and checks whether they can be used as a basis for the definition of levels and layers in the present document.

3.2.3.2.2. Step 2 – Identify candidates of existing (C-)ITS architectures

This step identifies existing (C-)ITS architectures that are potential candidates for the fol-lowing steps of the bottom up approach. Partially this analysis superimposes on existing documents analyzing the current situation.

3.2.3.2.3. Step 3 – Analyze candidates with regard to their frame structure

The candidates identified in the previous step are thoroughly analyzed. Basis for this analysis are the following aspects which in parts are derived from those already addressed in the report ’Recommendations for the Development and Maintenance of National ITS Architectures’ [Kr ¨uger et al., 2013]:

• what level is addressed

• what layers are addressed

– specific details beyond organizational, functional, technical

• where is it applied (reference implementation, real-life example)

• special requirements that need to be considered in the overall architecture

The first two aspects from the list will allow to classify the respective architecture and sort it into the general architecture structures from the first thoughts in section 3.2.1. The crite-rion of where it is applied helps to integrate it in the diverse structure of ITS architectures.

The aspects of being in use and location of implementation support considerations on both the temporal and spatial applicability.

The results of this analysis finally are consolidated, so that a conclusion is possible on how to deal with the candidates when drafting the overall architecture and decide which requirements a candidate brings in need to be considered (and where).

3.2.3.2.4. Step 4 – Derive levels and layers from existing ITS and C-ITS architectures Finally, a consolidated view on thelevelsandlayersused in existing ITS and C-ITS archi-tectures can be derived. Later this is taken into account when combining the results of the Top Down and Bottom Up Approach.