Conceptual modelling involves the formalisation of domain knowledge in a high-level, application-independent, yet authoritative and rigorous way. The conceptual modelling aims the development of a knowledge base for product support.The knowledge base contains two models: architectural and functional. The objective of the first phase is to organise data in a way that ensures homogeneity and validity of the resulting information. The use of ontological principles is deemed appropriate because of the formality and richness of ontological knowledge modelling. This approach takes advantage of some widely accepted notions in KE, such as concept, instance, and relation. Concept is a class of objects from the real world. Instance is something that specifies a concept by illustrating a real world object that belongs to that concept, such as Peugeot 206 (A) for the notion of cars. Relation is an attribute shared by objects in the subject domain that links and/or constrains them. One of the main ontological relations is generalisation. For example “car is-a vehicle” (C) is a generalisation type of relation. In addition to these main ontological elements, this approach suggests the use of new structures, such as domain and connector. These are employed to enrich the representation ability of the system. Domain is a hierarchy of concepts (i.e. concepts linked with “is-a” relation), which describes a part of the real world and is a concept itself. For example a domain “Product” (D) includes the hierarchy “car is-a vehicle is-a Product”. Relations that associate different domains are called connectors.The structural components described above, except for instances and their associations, enable the composition of the architectural model. The aim of the second phase is to put the structured information into productive use, within the context of product support. During this phase the architectural model is enriched by employing two new notions, knowledge-specifier and arc, which are further used in defining predicates and cases. Knowledge-specifier is a property that is considered so significant within the application domain that it is represented as a different concept. For example, it may be useful to know whether a product is viewed as complex or not, since that can define the way in which the support provided is adapted. Therefore, a knowledge-specifier called “ProductType” (G), which defines product’s complexity, is introduced. The level of the product support will be determined using mechanisms that include “ProductType”. Arc is a relation that links the knowledge-specifiers with other concepts and/or domains. Connectors can be characterised as active or inactive depending on whether the real world components they describe exist or not. The possibility of having such cases is represented by the connector-dependence (CD) measure. CD can take two values and be either true or false depending on whether the connector is always active or not. The notions introduced enable the creation of the system’s functional model. The combination of the architectural and functional models results in the development of the system’s knowledge model.