Servers, Groups, And Items
There are three key concepts to understand when attempting to grasp the OPC Data Access Specification. OPC servers, groups of items (tags), and the items themselves. An item can be thought of as the actual point being measured such as a thermocouple, pressure transducer, or an amplitude measurement. A group is a logical container for a set of items where items can be organized based on methods devised by the user. In many cases, only a single group is created and contains all of the measured items. But in many other cases, the user may wish to logically group items based on criteria such as location, transducer type or measurement type, and will create a group for each of these locations, transducer types, or measurement types etc.