Define a data model

A data model is defined using one or more properties files in an Oracle Policy Modeling project. These properties files contain the attributes, entities and relationships for the project. Having this information contained in a properties file for the project, rather than in individual Word and Excel documents, eliminates the need to re-add the same attributes, entities and relationships in each rule file.

Entities

An entity can represent a thing such as a person, a child or a corporation, about which attributes can be collected. An entity can have multiple instances. For example, data can be collected and inferred about more than one child in the same session.

Relationships

Relationships are the connectors between instances of an entity. By specifying the relationship you are specifying whether an instance of an entity is related to one or more of the instances of another (or even the same) entity group.

Attributes

An attribute is a single unit of data or fact. An attribute is of a particular data type: boolean, text, number, currency, date, time of day or date and time, and the value of an attribute can be 'known' or 'unknown'. An attribute always belongs to a particular entity even if it is the global entity.

An example of a data model

Let's say we want to capture the entity relationships for a family who may have children. There may be twins amongst the children. The children may go to school and the siblings may go to the same school or different schools. Each child has friends which may be the same friends as their siblings but they each have a single best friend who they do not share with other siblings.

Choose entities

We can capture this example using three entities:

the child
the friend
the school

We do not need to create a separate entity for the twin, as we know the twin is one of the children. Similarly, we do not need to create a separate entity for the best friend as we know that the best friend will be one of the child's friends. We do not need to create an entity for the family as we do not need to enter multiple families, so information about the family can be represented in the global entity.

Choose relationships

Containment relationships must be defined for each entity. Additional reference relationships are also defined where required for the data model logic. In our case, we know that:

a family (represented in the global entity) has children, so there must be a relationship between the global entity and the child
each child has a friend so there must be a relationship between the child and the friend
each child has a best friend, so there must be a more specific relationship between the child and the friend
some children may be a twin so there must be a relationship between the child and itself
children go to school, so there must be a relationship between the child and the school

We don't know:

whether it is important to know, for a particular school, which children go to that school
whether it is important to know, for a particular friend, which children they are friends with

We can either model these last two relationships 'just in case' or not capture these relationships. We have left these relationships out of this example for simplicity.

Choose relationship types

Now we need to decide what type of relationship there is between each of the entities. There are two questions you can ask yourself to help identify the type of relationship. (NOTE: The text in parentheses is the relationship text.) This will also help you see which relationships can be containment relationships (which must be "to-one" relationships to the containing entity).

Global entity and Child (the children):
Can more than one family have the same child? No.
Can there be multiple children in the family? Yes.
Therefore it must be a one-to-many relationship.
This will be the containment relationship for the child entity.
Child and Friend (the child's friends):

Can the children share friends? Yes.

Can a child have more than one friend? Yes.

Therefore it must be a many-to-many relationship.
Child and Friend (the child's best friend):

Can children share best friends? No.

Can a child have more than one best friend? No.

Therefore it must be a one-to-one relationship.
Child and Child (the child's twin):

Can more than one child share the same twin? No (otherwise it would be a triplet).

Can a child have more than one twin? No.

Therefore it must be a one-to-one self-referential relationship.
Child and School (the child's school):
Can the children share a school? Yes.
Can a child go to more than one school? No.
Therefore it must be a many-to-one relationship.
Containment relationships are also required for the Friend and School entities, since the above relationships for these entities are not suitable "to-one" relationships. We would define:
- Global entity and Friend (the friends): this is a one-to-many containment relationship.
- Global entity and School (the schools): this is a one-to-many containment relationship.

The relationships about which we wish to reason therefore look like: