Final answer:
Service mapping tools identify applications and define the discovery source with alphanumeric values, which allow for descriptive and identifiable source names.
Step-by-step explanation:
Applications discovered by service mapping typically have alphanumeric values defined for the discovery source field. Service mapping tools are designed to automatically discover services on a network and create a map of the relationships and dependencies between application components. The discovery source field is used to indicate the method or process that identified the application, and since it is a descriptor of a process or tool, having alphanumeric characters allows for a more descriptive and identifiable source name than purely numeric or boolean values. It should be noted that a specific ITSM platform, like ServiceNow, would have its own set of definitions for the discovery source field within its service mapping process.