A Mapper is a class which has to be written by developers of application searches for each Search Service. Its function is to transform data from the application into a format which can be written onto the staging database and imported into a Index. The transformation involves identifying relevant Entity properties of interest to the Search Service, constructing a list of these values and mapping them to a single consolidated text value. This value, stored in the staging database, is used later in the construction of a single search index Document. Every Search Service that is written must provide its own Mapper implementation.