Benjamin Mörzinger, Thomas Trautner, Iman Ayatollahi, Thomas Weiler
This ontology heavily relies on the SSN/SOSA ontology which are ontologies developed to describe observations made by sensors in a general (domain independent) way. It is divided into two parts, SSN which represents a detailed view and SOSA, which is a subset, containing only the most important concepts. The goal of this ontology is to facilitate interaction of data generating devices from a wide range of application areas.
Furthermore, it does not only cover the process of sensing (observation), but also actuation and sampling. For the scope of this thesis, however, only the part that is concerned with sensing is relevant. The respective concepts and their relations are depicted in the following Figure.
Not all of the depicted concepts are directly relevant for the scope of this thesis. Those that are however, are Sensors, Observations, Features of Interest and Properties. Furthermore, the concepts system and Platform will be reused by the domain specific production systems ontology.
In the context of SSN, Features of Interest can be anything physical (a tree, a car, a group of people) which is is of interest for some application. Features have properties, which can be observed to directly or indirectly (through calculation) arrive at results. For example, a property of a car might be its fuel consumption.
Observations are generated by Sensors and are associated with properties of Features of Interest. For example, a given Sensor can repeatedly measure the temperature within a room. Each measurement would in this case be an Observation of the Property "Temperature" of the Feature of Interest "Room". The result of such an Observation would simply be a single value. Such Results, however, can also be more complicated in nature. Other forms of Results might be images or structured data.
Finally, there is a distinction between Systems and Platforms. Systems represent pieces of infrastructure which can be organised hierarchically (systems can themselves be part of systems). Systems can furthermore be distinguished into Sensors, Actuators and Samplers. This is useful to describe, for example, that a sensor is part of a larger system or that parts of a system are also sensors. In contrast, the Platform concept covers any entity that hosts other entities.
Based on the previously described SSN ontology, another ontology with domain specific terms for the manufacturing domain was developed. The scope of this ontology was, to be able to talk and reason about concepts that are concerned with manufacturing processes and their outcomes. In the form of MASON, a similar, but slightly different ontology exists. The difference, however, is the emphasis on the process nature and the necessity to associate sensor readings (observations) with those processes as well as their outcomes.
The result of the development process is depicted in Figure.
In the center of the ontology stand Manufacturing Processes. Such processes can, in accordance with DIN 8550 be further distinguished into one of the six main process groups Change Properties, Coating, Joining, Cutting, Forming and Primary Forming \hl{CITE}. Furthermore, processes can themselves have subprocesses which makes it possible to describe more sophisticated manufacturing processes which often cover several different process steps. Potentially, this can also be used to distinguish phases within manufacturing processes. In the case of drilling, one might for example want to describe that a given drilling process is the combination of two process steps (tapping before drilling). The potential to use this to describe temporal dependencies of processes is obvious and will be further discussed below.
The result of any Manufacturing Process is a Geometric Feature, which is associated with a particular Workpiece. Geometric Features are particular kinds of shapes that workpieces might have such as holes, corners and pockets.
Manufacturing Processe are executed by Machining Rigs. Those are Platforms in the sense of the SOSA ontology and are (potentially) complex combination of Systems such as Production Machines, Fixtures, Tools. Some of these systems can also be considered to be Sensors (i.e. they generate data). An example for an entity that would be considered both a Tool and a Sensor is a sensoric tool holder.
Each Machining Rig has at least one assigned Operator, which is a natural person in charge of carrying out processes on the specific rig. Furthermore, the concept of Project is used to describe entities that motivate the manufacturing of a set of workpieces and potentially define the required Machining Rigs.
Finally, as can be seen, almost all of the defined concepts are also considered to be Features of Interest, which makes it possible to define Properties which might be subject Observations. For example, a Workpiece "Test Speciment" might have several Geometric Features "Boreholes", which in turn have Properties such as "Surface Roughness" or "Roundness" which might be observed through an Observation "Quality Measurement".