The Direct Approach goes on the assumption that every Address must have a Street Address, and that the location of that Street Address is known in advance. These are probably untenable assumptions, but it is useful to follow them through.
To describe the calculated fields requires the invention of a SQL-like language that, in its entirety, is beyond the scope of this book. The stripped down version, however, includes two very important functions, first encountered in a very clever database management system that is now unknown, but which your author first encountered in 1981.[(] The functions address two very important navigation activities:
· INFER-THROUGH(<role name>, <parent entity class name>