A [i]group[/i] is a named set of attribute keys. An attribute key can belong to many groups or none at all. An [i]attribute key[/i] describes named values attached to a particular type of object. Each instance of this entity contains the attribute's description and its name. An attribute key name must consist of letters, numbers, periods, underscores, and hyphens. Text describing the attribute. This should explain what the attribute means and what kinds of values are appropriate. ERDB data type for the attribute. This serves as documentation only, but that may change at some future point. An [i]object[/i] represents a keyed thing to which an attribute can be assigned. In order to improve performance, this table has no data in it. It is simply required by the semantics of the database. This relationship connects an attribute key to the groups of which it is a member. This relationship connects an attribute key to its objects. It contains the attribute values, and is therefore the primary data repository for the database. This is the actual attribute value. Note that a single key/object pair may in fact have many values, and therefore many entries in this table.