A computer-implemented method for designing a health management system for monitoring the condition of a platform, the platform comprising a plurality of primary sub-systems, the health management system being represented as a hierarchical structure of information layers including a stakeholder layer, an information requirements layer adjacent to the stakeholder layer, a data requirements layer adjacent to the information requirements layer, a data transformation layer adjacent to the data requirements layer, a sensors layer adjacent to the data transformation layer, a sub-systems layer adjacent to the data transformation layer, and connectors (214, 226) representing data or information transfer paths between said layers, and the method comprising, in order: prompting a user to populate the stakeholder layer with information identifying a plurality of stakeholders of the platform; prompting a user to populate the information requirements layer with information requirements of each of said stakeholders, wherein each information requirement defines information required by one or more of said stakeholders from said health management system; prompting a user to populate the data requirements layer with data requirements corresponding to said information requirements, wherein said data requirements define data required to fulfil said information requirements; prompting a user to identify the primary sub-systems by populating the sub-systems layer with the platform sub-systems that are capable of providing the raw data necessary to fulfil the data requirements; defining a sensor array comprising sensors suitable for providing output signals relating to condition characteristics of the primary sub-systems by: identifying existing sensors of the identified primary sub-systems having output signals suitable for conversion to fulfil the data requirements; identifying unfulfilled data requirements that cannot be fulfilled by the existing sensors; and prompting the user to identify new sensors for inclusion in the sensor array so as to provide output signals suitable for fulfilling said unfulfilled data requirements; prompting a user to populate the data transformation layer with procedures for converting the output signals from the sensor array to the data requirements, thereby to fulfil the information requirements of the stakeholders; and prompting a user to provide the connectors between: each stakeholder in said stakeholder layer and their respective information requirements in the information requirements layer; each information requirement and its respective data requirements in the data requirements layer; and the sub-systems layer and the sensors layer. prompting a user to populate the stakeholder layer with information identifying a plurality of stakeholders of the platform; prompting a user to populate the information requirements layer with information requirements of each of said stakeholders, wherein each information requirement defines information required by one or more of said stakeholders from said health management system; prompting a user to populate the data requirements layer with data requirements corresponding to said information requirements, wherein said data requirements define data required to fulfil said information requirements; prompting a user to identify the primary sub-systems by populating the sub-systems layer with the platform sub-systems that are capable of providing the raw data necessary to fulfil the data requirements; defining a sensor array comprising sensors suitable for providing output signals relating to condition characteristics of the primary sub-systems by: identifying existing sensors of the identified primary sub-systems having output signals suitable for conversion to fulfil the data requirements; identifying unfulfilled data requirements that cannot be fulfilled by the existing sensors; and prompting the user to identify new sensors for inclusion in the sensor array so as to provide output signals suitable for fulfilling said unfulfilled data requirements; identifying existing sensors of the identified primary sub-systems having output signals suitable for conversion to fulfil the data requirements; identifying unfulfilled data requirements that cannot be fulfilled by the existing sensors; and prompting the user to identify new sensors for inclusion in the sensor array so as to provide output signals suitable for fulfilling said unfulfilled data requirements; prompting a user to populate the data transformation layer with procedures for converting the output signals from the sensor array to the data requirements, thereby to fulfil the information requirements of the stakeholders; and prompting a user to provide the connectors between: each stakeholder in said stakeholder layer and their respective information requirements in the information requirements layer; each information requirement and its respective data requirements in the data requirements layer; and the sub-systems layer and the sensors layer. each stakeholder in said stakeholder layer and their respective information requirements in the information requirements layer; each information requirement and its respective data requirements in the data requirements layer; and the sub-systems layer and the sensors layer.