This page describes the proposal to restructure the data modeling activities within COVESA. First, the current state is presented to provide the necessary context. Then, the proposal is introduced.

Current setup (description)

So far, the data modeling activities in COVESA have been primarily centered on the continuous development and maintenance of the Vehicle Signal Specification (VSS) and the tools that parse VSS into different formats. In the current setup, there is no clear description of what requirements (i.e., functional and non-functional) are driving the design of the data model. It seems that the primary purpose of VSS is to serve as a naming convention for the properties of the vehicle. Nevertheless, there is little attention given to the separation of concerns:

• On the one hand, there is the "conceptual area," where the controlled vocabulary has to be described and adequately documented. Data models belong to this area because they define the entities of interest in a particular domain and the possible relationships between them.
• On the other hand, we have the "application area," where a data model is used in specific implementations (e.g., databases, applications, etc.).

The figure above shows how VSS modeling belongs to the conceptual area. To use the specification described in VSS (i.e., a "vspec" file), one has to parse it into a specific format (e.g., JSON) by using the VSS tools. The tools are the mechanism that makes the VSS data model usable in the application area. From the practical point of view, the application area needs a specific schema that determines the structure in which the data is to be stored. In this context, we mean long-term storage (e.g., a database) or short-term storage (RAM and variables' allocation during application execution).

In the current setup, the whole data model is taken one-to-one and parsed as the schema for the application area. Then, it is up to the specific implementation to use custom mechanisms to ignore the overhead when only some concepts defined in the data model are required or used. Although this aspect has shown no significant limitation until now, it becomes relevant when multiple domains are involved. Therefore, with the increasing interest in adding other domains apart from vehicle-specific data, it is crucial to define a data modeling strategy that can scale beyond tree hierarchies and vehicle-specific data.

Proposal overview (description)

The idea is to define the data modelling workflow for COVESA in terms of the conceptual area (i.e., development and maintenance of the controlled vocabulary) and the application area (i.e., tools that construct a usable schema out of the data models for a particular use case).

• In the conceptual area, there should be a clear step-by-step guide on how to work with two different levels of expressiveness. This consideration is needed because a tree hierarchical model (what VSS has been so far) is not the best model type to handle some upcoming needs, such as data integration. Hence, the model might be selected depending on the user needs.
  • (less expressive) Tree hierarchical model, good for:
    • Information classification according to a given criteria (e.g., taxonomy, meronymy, custom tree.)
    • Naming convention following a dotted notation (i.e., concatenation of the branches)
  • (more expressive) Ontology, good for:
    • Data integration
    • Concepts re usability
    • Reasoning
    • Multiple hierarchies
    • Knowledge representation
• In the application area, the tools have to provide a mechanism to arbitrary select concepts of interest from one or multiple domains, including the context and pointers to the uniquely identified definition of the concepts.

In other words, the proposal is not to enforce the use of ontologies. It is rather providing a common agreement on how and when to use what data model. The idea is better explained with the following diagram:

•  
  • will be responsible for the standard definition of the controlled vocabulary. Here 

• The specific aspects of the proposal are illustrated in the following figure, and explained below:

1a - Generic domain tree modelling approach

The simplicity of VSS has proven to be a successful approach for the continuous contribution of Subject Matter Experts (SMEs); just by modifying a text file, discussing the changes, and creating a pull request. The approach itself should be generalized to serve as a guideline to describe and maintain one hierarchy. The idea here is to abstract the modelling approach used in VSS and describe it with generic terms that might be re used with other domains.

1b - Tree model suitability rule-set

Having an stablished approach to model a tree hierarchy does not mean that COVESA should motivate the arbitrary creation of multiple trees. Therefore, it is essential to define a simple set of rules that are to be satisfied before starting a new data tree that is to be developed and maintained by COVESA. Such a rule set can include, for example:

• There must exist the proven need for at least 3 branches.
• Each branch must have at least 2 leaves.
• The implicit relationship between consecutive branches must be documented.
• There must be no cross references to other existing data models.
• Branch names must use this XYZ format

2 - Tree-to-ontology sync mechanism

3a - Domain ontology modeling approach 

3b - Covesa core ontology

3c - Other data model(s)

4 - Custom data schema construction mechanism