The links defined by the rules below connect entities in particular, structured ways (see Figure 1). In database terms, each record in the entity tables can connect to 0, 1, or many records in the link table.

The entity tables are on the outside of the diagram (Name, Intervention, Vocab, Event, and Diary). The LINK table is in the center. Note that each of the lines connecting an entity table to the link table ends at the link table with a zero and a "crow's foot" branch. The line defines a 1:m relationship between the ENTITY tables and the LINK table.

The Name, Event, and Intervention tables are called BASIC tables because they will give meaning and context to the rule-instance records the user builds. Vocab contains the controlled vocabulary items and the category structure which organizes the items.

The Diary-Link structure may be implemented slightly differently in different versions. In a standard relational model (see Section 8.1), Diary and Link may be embedded in the same tables. In abstract or more highly relational models (Sections 8.2, 9), the Diary table contains the master records for the rule-instances; the actual data for the rule-instances is kept in the Link table.

As stated earlier, the Data Model proposed by this working group does not specify exactly how the link works in any given implementation of these standards. The link structure might be a collection of standard relational tables, or it might use a more sophisticated, more highly normalized technique. At a minimum, for a given implementation to be compatible with this standard, we specify that it must be able to represent information in the form of the three rule-types, and be able to manage all of the rules proposed in the following section. It should be emphasized that these are minimum standards -- much greater detail and analytical power are possible.