The ProductSpecification represents a product specification as perceived by the business user and specifies what the marketing operator wants to sell at a functional level (i.e. what are the capacities, which usages are available…).<br/>It can represent:<br/>        • material goods (Terminal, phone, mobile, fax, modem)<br/>        • or intangible goods (like an Anti-Spam service for email – that will be deployed on a traditional network or in a cloud)<br/>When the ProductSpecification represents tangible goods, it is associated with a ResourceSpecification. Corresponding Resources are stored in warehouses or bought to a supplier on demand.<br/>When the ProductSpecification is intangible goods, it is either realized as a CustomerFacingService (when the Service Provider is able to realize it) or bought as a ProductSpecification proposed by a Supplier (when the Service Provider is not able to realize it). For example, a Broadband know-how might be built or bought depending on the location of it.<br/><br/>Since a CustomerFacingServiceSpec defines which ResourceFacingServiceSpecs (i.e. technical solution) can answer the CFSSpec requirements, the ResourceFacingServiceSpec can be used to determine which ResourceSpecifications might be required for a given Product. <br/>A CompoundResourceSpec can of course be used as “shorthand” to refer to the appropriate set of PhysicalResourceSpecs and / or LogicalResourceSpecs, if desired.<br/><br/>For now, the basic relationship between ResourceFacingServiceSpec and ResourceSpec as defined previously is sufficient. <br/><i>Note that the SID QoS defines further detail on the relationships defined in the following figures.</i><br/>