## 2 Background  
### Knowledge-Based Engineering and Knowledge-Based CAD  
The concept of knowledge-based engineering (KBE) involves a shift in computer-aided product modeling from documenting a single product variant to modeling solution spaces where a variant can be found to meet a set of requirements [6; 7]. Two fundamental questions must be answered when building a KBE system: how to model the solution space, and how to explore it to achieve a design task [5; 22].  
In algorithmic modeling, the focus is on automating the design process rather than pre-formulated solutions [4; 23]. Algorithms are used to extract product properties from requirements and build product design rules, also taking into account external data or numerical simulations [24; 25; 26]. Therefore, a parametric product master model is unnecessary, as this approach aims to generate an individual product for each set of customer requirements. This is particularly favorable for complex geometries and pure configuration designs but largely restricts subsequent parametric editing of the variant. Instead, requirements and design rules need to be altered to create the updated version [27; 28; 29].  
When using parametric design, editing a product model is made easier, allowing for geometry re-use and also embedding design intent with geometry [18; 30]. Defining logical and mathematical relations between parameters helps differentiate leading and driven parameters. The designer models geometry and plans configuration concepts and parameterization of the component [7; 31; 32]. Today's CAD system can create user-defined parameters not only for length or angular dimensions but also to support the computation and handling of other units such as for stresses, forces, or moments of inertia. This feature allows for the direct integration of comprehensive dimensioning formulas into the CAD model, making it more efficient and convenient for users to work with [33]. Furthermore, some CAD systems offer the option to specify design rules. These rules usually take the form of if-then-else statements, which link, e.g., the suppression of specific features to geometric or other parameters [34; 35].  
As components become more complex, the need for a well-structured configuration with parameters at various levels becomes increasingly imperative. Assemblies may contain a skeleton model that defines the positioning of components and their geometrical characteristics based on a structural design. The skeleton itself can have different features and relations to its child models, e.g., the skeletal geometry can be used as a reference model or its geometric parameters can be linked to the child models via equations or by design rules [18; 19].  
The control of parameters can also be externalized. Most CAD systems allow for linking or embedding spreadsheets, providing additional mathematical and statistical capabilities compared to the CAD system alone. Lookup tables can be integrated for selecting standard parts based on geometric or load information. With this, basic reasoning functions are available [33; 36]. Other ways of integrating reasoning are the use of script languages and macros within the CAD system and coupling external knowledge-based systems for parameter determination [18; 33].