Explanation:

In the context of modelling, the knowledge-based approach is not considered as one of the approaches. The rule-based approach and the learning-based approach are two common strategies used for modelling, while the knowledge-based approach is not typically recognized as a separate approach.

1. Rule-based approach:
The rule-based approach involves creating a set of predefined rules or conditions that are used to make decisions or predictions. These rules are usually developed based on expert knowledge or domain-specific knowledge. The advantage of this approach is that it allows for explicit control over the decision-making process. However, the main limitation is that it requires a large number of rules to cover all possible scenarios, which can be time-consuming and difficult to maintain.

2. Learning-based approach:
The learning-based approach, also known as the data-driven approach, involves training a model using a dataset that contains examples of input and corresponding output. The model learns from the data and generalizes patterns to make predictions or decisions on new, unseen data. This approach is widely used in various fields, such as machine learning and artificial intelligence, as it allows for automatic learning and adaptation to different scenarios. The main advantage is its ability to handle complex patterns and large amounts of data. However, it requires a sufficient amount of high-quality data for training and may not always produce interpretable results.

3. Knowledge-based approach:
The knowledge-based approach, although not considered as a separate approach for modelling, is often integrated into rule-based or learning-based approaches. It involves incorporating expert knowledge or domain-specific knowledge into the model. This can be done by formulating rules or constraints based on the available knowledge or by using ontologies or knowledge graphs to represent and reason with the knowledge. The knowledge-based approach enhances the interpretability and explainability of the model's decisions. However, it may also require significant effort in acquiring and formalizing the knowledge.

In summary, while the rule-based and learning-based approaches are commonly used for modelling, the knowledge-based approach is not considered a distinct approach but rather a component that can be integrated into the other approaches. Therefore, the correct answer is option 'C' - the knowledge-based approach is not an approach considered for modelling.