As discussed in the section of the Watson Explorer Engine Users Manual entitled Watson Explorer Engine Applications and Services, Watson Explorer Engine applications typically require that certain services are running on any host that can deliver search results in response to a query.
In traditional end-user Watson Explorer Engine installations, an application known as query-meta typically receives queries from Watson Explorer Engine search applications and forwards them to the Watson Explorer Engine Search Service. The Search Service (also known as the Query Service) then uses the Watson Explorer Engine sources that are referenced in the query to identify the search collection(s) that should be queried, their location, and submits the queries to them.
API-based Watson Explorer Engine applications work slightly differently. Watson Explorer Engine applications interact with a core application known simply as velocity. Queries made through the Watson Explorer Engine API are forwarded to the Search Service if the query-search API call is used, or to the Collection Broker if the query-search API call is being used. In the latter case, the Collection Broker then contacts the Search Service.
The Watson Explorer Engine Search Service is typically started at boot time by the velocity-startup command, which is documented in the Watson Explorer Installation Guide, or in the System Administration section of the Watson Explorer Engine Users Manual. The Search Service can also be started programmatically, by executing the Starting the Search Service function.
The Watson Explorer Engine Search Service must be running in order for it to be contacted by the query-meta application, the velocity application, or the Collection Broker. The Collection Broker starts automatically when any Collection Broker-related function is called (with the exception of the collection-broker-status function), but can also be started explicitly, as discussed in the next section, Working with the Collection Broker. Later in this document, Working with the Search Service discusses how to start, work with, and stop the Search Service.