2.2. Ontology-related literature
Given its closely related focus (despite not overlapping with ours, content-wise), we relied on ExtruOnt, an
ontology for the description of an extruder components proposed by Ramírez-Durán et al. [61], as a gold
standard for the development of our knowledge base, adhering to the authors’ methodological, design, and
presentation choices.
With a broader scope, other upper or domain ontologies for AM have been proposed in the literature. The
Manufacturing’s Semantics Ontology (MASON) [49] is an upper ontology for the conceptualisation of core
additive manufacturing domain notions. The US National Institute of Standards and Technology (NIST)
propose an ontology for AM, that we label NIST AM [80, 81], to support the development of laser and
thermal metamodels. Towards interoperable knowledge and data management in applications, Sanfilippo
et al. [66] introduce another ontology for AM (Onto4Additive), based on the upper Descriptive Ontology
for Linguistic and Cognitive Engineering (DOLCE) [13].
Other related AM ontologies include the following (cf. also literature reviews in Sanfilippo et al. [66]
and Ramírez-Durán et al. [61]): the Additive Manufacturing Ontology (AMO) [1], based on the upper Basic
Formal Ontology (BFO) [3]; the Innovative Capabilities of Additive Manufacturing (ICAM) ontology [34];
a Smart Applications Reference (SAREF) [23] extension for semantic interoperability in the industry and
manufacturing domain (SAREF4INMA) [18]; the Semantically Integrated Manufacturing Planning Model
(SIMPM) [73]; the Manufacturing Resource Capability Ontology (MaRCO) [37]; the Manufacturing Service
Description Language (MSDL) ontology [2]; the Politecnico di Milano–Production Systems Ontology (P-
PSO) [28]; the Ontology of Standard for the Exchange of Product model data (OntoSTEP) [8]; the ontologies
proposed by Dinar and Rosen [21], Liang [52], Roh et al. [64], and Li et al. [50]. Finally, within the EU-funded
project EMMC, the recently proposed European Materials Modelling Ontology (EMMO) [36] provides a
standard representational upper (nominalistic) ontology framework based on state-of-the-art knowledge on
material modelling and engineering.
3. Ontology design and development
To develop our ontology, we followed the approach proposed by Ramírez-Durán et al. [61], with the adoption
of the NeOn Methodology [77] and in particular of the Six-Phase + Merging Phase Waterfall Ontology
Network Life Cycle Model. This model, allowing for a flexible interplay between pre-existing ontological
and non-ontological resources, consists of the following phases, which will be detailed in the remainder of
this section: initiation, reuse, merging, re-engineering, design, implementation, and maintenance.
3.1. Initiation phase
As by the methodological framework of Suárez-Figueroa et al. [76], we initially developed an Ontology
Requirements Specification Document (ORSD), summarised in Table 1, with the following goals: defining
the purpose and the scope of our ontology; selecting the implementation languages; identifying intended
users and uses of the ontology; formulating in natural language groups of competency questions (CQs), to
be expressed and answered by our ontology; providing a pre-glossary of terms appearing in the CQs.
To better illustrate the purpose and the intended uses of our ontology, we present the following simplified
scenario, involving a MAM production service monitored and regulated by a control system relying, for
instance, on a machine learning architecture. Suppose that, during a 3D printing process, the monitoring
system detects a feature that is classified (by means of, e.g., a pre-trained convolutional neural network) as
a porosity defect, consisting of a void encapsulated within bulk material. Moreover, assume that the system
controller (based on, e.g., a reinforcement learning mechanism), in an attempt to mitigate the propagation
of the feature, sequentially modifies relevant build chamber parameters, powder handling and deposition
system parameters, and the laser scanning speed, observing that only the latter has an impact on limiting
the defect. The purpose of our ontology is to formalise the domain knowledge required to infer that the
detected porosity is an instance of a process-induced defect, rather than of an equipment-induced one (given
that all other possible equipment-related parameters have been ruled out as influences on the feature).
3