## 4 Case Studies
### Sketch Exchange via STEP  
As the first example, we use the exchange of a rhombic-shaped sketch between the CAD systems Creo Parametric 6.0.5.0 (Parametric Technology Corporation, Bosten, MA,  
Figure 6: Key findings of the item adaption. USA) and Catia V5 2019 (Dassault Systemes, Velizy-Villacoublay, France), which Figure 7 illustrates below. Sketches are a commonly used design element. A significant feature is that they are colored after being transferred from a source to a target system. For example, automatic recognition uses coloring to determine specific geometries [56]. However, the import of a colored sketch, which is created in Creo and exported as a STEP-AP214 file and then imported into Catia with standard settings, results in a loss of color information, even though potentially all data for the coloring is available in the transfer file [15]. As a result, the sketch is blanket colored in white by the postprocessor of Catia. The analysis of a STEP-AP214 exchange file from Creo and Catia results in generally valid item structures in the first step. Each file stores a sketch, and Figures 8 and 9 illustrate the extracted assemblies. Attributes, such as the names and lengths of individual instances and the references used, are generalized to make the structures comparable, independent of the concrete use case. Figure 8 demonstrates that the preprocessor applies indirect coloring in the Creo case. More precisely, the DRAUGHTING_PRE_DEFINED_COLOUR (ref.8) instance, which contains the color information in attl.14, is linked to a single curve segment via the STYLED_ITEM (ref.14) instance. The curve segment is then connected to the initial instance, COMPOSITE_CURUVE (ref1.1), by references ref1.2 and ref1.3. An analysis of the TSI in Figure 9 shows that the postprocessor of Catia expects direct coloring of the initial instance COMPOSITE_CURVE (ref2.1). Accordingly, the entity SYLED_ITEM (ref2.2) directly refers to the initial instance. Figure 8: Source system (Creo) conforms to the item structure of the sketch coloring. Figure 7: Lossy data exchange of a sketch between the CAD systems Creo and Catia. Figure 9: Target system (Catia) conforms to the item structure of the sketch coloring. In both cases, the entities MECHANICAL_DESIGN_GEOMETRIC_PRESENTATION_REPRESENTATION (ref1.9 and ref2.7) provide a representation. The instances link to direct and indirect coloring, respectively. In the second step, defining the relationships between the item structures developed in the previous step is necessary to highlight the differences that cause incompatibility. Figures 8 and 9 show the conditions on the right side. The initial instances COMPOSITE_CURVE (ref1.1 and ref2.1) are identical in both setups, and the data are thus homogeneous. As the postprocessor of Catia expects immediate coloring, which the preprocessor in Creo does not provide, a direct coloring of the initial instance must be newly generated. Due to non-existence, we declare information ref2.2 to ref2.6 as positive. Catia does not require the original indirect coloring for an error-free import, but it does not interfere if it is retained. Thus, instances ref1.2 to ref1.8 are neutral. Both structures contain the entity MECHANICAL_DESIGN_GEOMETRIC_PRESENTATION_REPRESENTATION (ref1.9 and ref2.7). Furthermore, the exported instance misses a reference to the entity STYLED_ITEM, which we need to generate in the context of immediate coloring. Due to missing information, data ref1.9 and ref2.7 must be classified as heterogeneous. The third step is the actual adaptation of the item. Figure 10 shows a specific adapted item. In the case of the generalized, newly added attributes att2.4 and att2.5, standard-compliant values from ISO 10303-214 are inserted [50]. For att2.6, the attribute \"blue\" is inputted, which is already found in the extracted item from Creo. The heterogeneous entity MECHANICAL_DESIGN_GEOMETRIC_PRESENTATION_REPRESENTATION references the STYLED_ITEM (#196) instance of the newly added direct coloring with the references #196 to #200.