The skeletal dysplasia domain is characterised by highly complex, heterogeneous and sparse data.In this domain, the analysis and interpretation of new patient cases relies on comparisons to past case studies due to the absence of defined guidelines and the lack of mature domain knowledge for this group of genetic disorders. In order to carry out the analysis and interpretation of new patient cases, practitioners currently query many heterogeneous data sources and aggregate diverse types of data. This integration represents a significant challenge due to the extreme heterogeneity of the data models, metadata schemas, vocabularies and data formats and inconsistencies in naming and identification conventions. Therefore, there is an urgent need to investigate the development of medical decision support systems which can assist clinicians and researchers to improve their understanding of the causes, behaviours, symptoms and attributes of the diseases and assist them in the decision-making process (e.g., diagnosis).In the skeletal dysplasia domain, the absence of mature domain knowledge and the lack of documented and well-structured past cases, in addition to the general sparseness of skeletal dysplasia data, hinder the development of reliable decision support methods. In this thesis, the first step is taken towards developing a decision support framework in order to assist clinicians, doctors and researchers in this domain.The developed framework is a phenotype-disorder lifecycle to assist practitioners in finalising patient cases by going from phenotypes to disorders and vice versa. The framework was developed in four phases and combines ontological techniques with inductive and statistical reasoning techniques. In the initial phase, the underlying data characteristics were analyzed and a novel machine learning approach was developed to produce probabilistic candidate rankings, which can serve as support for medical decision-making (e.g., diagnosis). In the second phase, the semantics encoded in the domain were exploited in order to find possible disorders for a new patient case by developing a semantic similarity-based approach. In the third phase, to discover the implicit relationships between different ontological concepts (e.g., phenotypes and disorders), semantic similarity methods, formulated using the intrinsic structure of a given ontology, were combined with traditional interestingness measures in the process of discovering association rules. The final phase proposes a data mining approach for discovering characteristic features in the context of a set of disorders.From the data and domain knowledge perspective, the developed approaches and evaluation strategies led to a number of significant findings towards building a fully-fledged decision support framework; (i) the properties of data in the domain are rareness, sparseness, and high dimensionality; (ii) the domain knowledge introduced more noise compared to the noise produced ii by patient cases; and (iii) semantic similarity improves the overall...