DBMS-Weak Entity Types
Entity types that do not have key attributes of their own are called weak entity types. In contrast, regular entity types that do have a key attribute are sometimes called strong entity types. Entities belonging to a weak entity type are identified by being related to specific entities from another entity type in combination with some of their attribute values. We call this other entity type the identifying or owner entity type, and we call the relationship type that relates a weak entity type to its owner the identifying relationship of the weak entity type . A weak entity type always has a total participation constraint (existence dependency) with respect to its identifying relationship, because a weak entity cannot be identified without an owner entity. However, not every existence dependency results in a weak entity type. For example, a DRIVER_LICENSE entity cannot exist unless it is related to a PERSON entity, even though it has its own key (LicenseNumber) and hence is not a weak entity.
Calling Built-In Applications Using Intents Until this point, you have seen how to call activities within your own application. One of th...