## 2 Materials and Methods
### The BWMD Ontology  
The first step in generating semantically structured data is establishing a common vocabulary to be formalized in the form of an ontology and a data model, both of which are to be determined by the use case.  
An ontology consists of a collection of classes (hierarchically organized following the class-subclass relation), properties, and constraints. It aims to describe domain knowledge at a reasonable granularity for better reuse and understanding of the digitalized domain data. Hereafter, it is important to clarify that the classes of an ontology encapsulate a range of categories of objects or concepts that share similar attributes and behaviors. Meanwhile, the instances of a class represent a particular individual inside a given class.  
Within the framework of the project MaterialDigital [30], a domain ontology managing class hierarchy, object properties, and data properties was designed and implemented. This domain ontology was the product of the united efforts and extensive communication between different MSE domain experts. The developed domain module was directly merged with the BFO 2.0 top-level ontology [32] and received the name of 'BWMD Ontology' [33; 34]. The BWMD Ontology contains two layers: a mid-level ontology layer to model material-intensive process chains and a domain layer to model all process details related to the permanent mold casting process for AlSi10 Mg, manufacturing, and characterization processes (mechanical and analytical). The process chains modeled by the mid-level ontology concepts (classes and properties) include the processed objects and corresponding process-related data (raw data and analyzed properties), the involved process parameters, the involved machines, the necessary research equipment, infrastructure, and software. The BWMD Ontology also enables a simple description of the material structure, which can be specified for the chemical composition, the material volume, and the material surface. The BWMD Ontology does not include axioms beyond subclassing, and domains and range restrictions for object and data properties.  
Figure 1 schematically represents the connections between BWMD ontology classes and BFO classes. It exemplifies how the ow:class _engineering material_ from the BWMD Ontology is modeled as a subclass of (_is_a_) the BFO ow:class _object_. The BFO classes are shown in black and the classes specific to the BWMD Ontology are displayed in green. Details about how instances of these classes are related are expressed by the object properties, depicted in red. This straightforward representation illustrates how an _object_ can interact with a process as an 'input' or 'output' instance. A _chemical composition_ could be associated with a particular _object_ through the object property _hasStructuralInfo_, and each _object_ is associated with a specific object identifier through the object property _hasIdentifier_, which points to an instance of the class _identifier_, that could be more precisely represented  
by one of its subclasses, e.g., _object ID_ (to identify an object) or _material name_ (to identify a material). On the other hand, the concept of _dataset_ (e.g., a _chemical composition_) is modeled as a subclass of the IAO (Information Artifact Ontology [35]) owl:class _information content entity_, where an instance of _information content entity_ can be directly connected to a process, both as input and as output instance.