## 3 Proposed Method
### Description of the Individual Steps of the Compatibility Improvement Approach
#### 3.2.3 Third Step--Adaptation of Items  
Before the actual adaptation, we extract the items under consideration. Since the file originates from the source system, the SSI is the basis for the extraction process. Regular expressions (regex) are particularly suitable for the search. A regex describes an abstract pattern that matches a string of characters [55]. In particular, a regex is ideal for improved tracking. Furthermore, wildcards offer the opportunity to reach special operations. Search patterns can directly include standard operations since they represent the basic structure of an item and do not differ across items.  
If items are available, the applicant should first check whether they are already compatible. Conformity is present if only homogeneous or neutral conditions exist. Heterogeneous, positive, or negative conditions imply that individual instances of the item structures between the source and target systems differ. These then serve as the cause of the compatibility problem.  
If incompatibility can be determined, all defined conditions must be processed iteratively to consider all relationships and progressively create the compatible item. It is advantageous to start with the conditions on the SSI since newly generated information of the TSI may refer to already existing instances. Conditions involving SSI are either  
Figure 5: General structure of the item coordinate system for the CAD system Creo Parametric 6.0.5.0.  
homogeneous, heterogeneous, negative, or neutral. We keep information with a homogeneous condition unchanged since they do not differ. We need to remove the error-causing negative instances and adapt differing heterogeneous instances. Neutral conditions are a particular case. We can either keep or remove them since they are neither needed for a correct interpretation nor interfere with it. However, as retention ensures compatibility with the source system, this option is preferred.  
Subsequently, iteration of the instances of the TSI takes place. Here, we only consider positive ones since the pairwise homogeneous and heterogeneous conditions are already handled during the SSI iteration. Moreover, negative and neutral conditions occur only in connection with instances of SSI. We need to generate information with a positive condition since it does not exist in the transfer file so far. The values for the special operations result from references within the item and permissible values from the context or standards on which the format is based.  
At this point, we note a dilemma related to negative, positive, and heterogeneous conditions. More precisely, removing an instance with a negative condition, generating new information with a positive condition, and modifying data with a heterogeneous condition can all lead to misinterpretations in the source system. This circumstance is difficult to avoid. Consequently, creating a functional transfer file for both the source and target systems is challenging. We recommend a repeated inverse source system conform adjustment of the transfer file to reimport it error-free into the originating system.  
In summary, the results of the iterations of the third step are conform and insertable items. Figure 6 represents an overview of the conditions with their respective consequences on the right side and a summary of the first two steps described in the previous two subsections, outlined in dashed lines.