A typical data model report delivered to clients by ESI consists of a series of drawings of parts of the client's model, accompanied by explanatory text. The purpose of this report is not simply to document the model, but to do so in a way that can be understood by anyone with an interest in the subject--whether or not the person has any data modeling experience.
    Here follows an example of a segment of an enterprise model, plus the narrative that accompanies it. Note that the explanation is not just of the model itself, but also of
    why it is modeled that way.

    Employment
    It is common to specify EMPLOYEE as a sub-type of PERSON . After all, a large number of the people you want to keep track of are employees. This is wrong, however.
    A person is not inherently an employee. He or she only becomes an employee by entering into a relationship with a company. The quality of being an employee, then, is an aspect of a relationship, not of an entity. This is an example of a common problem in converting common English into a data model: many of the nouns we use combine the essence of a thing with its relationships to other things.
    What we want to say instead is that each PERSON may be employed by one or more ORGANIZATIONS and that each ORGANIZATION may be the employer of one or more people. This implies the creation of another entity, EMPLOYMENT, each occurrence of which is the fact that a PERSON is employed by an ORGANIZATION. This is shown in Figure 13.
    Each EMPLOYMENT, then, must be of one PERSON with one ORGANIZATION. Attributes of employment include "Employment date", "Termination date", "Social security number", and so forth.




    Figure 13: EMPLOYMENT

    The nature of that EMPLOYMENT is defined by the POSITIONS held during its course. A POSITION is a job in the company, as defined by a particular ORGANIZATION (either the company as a whole or a particular department).
    Figure 14 shows how each EMPLOYMENT may be the basis for one or more POSITION ASSIGNMENTS, where each POSITION ASSIGNMENT must be to a particular POSITION. As just described, the POSITION is defined by an ORGANIZATION.
    Note, by the way, that it is possible for a PERSON to be employed by (an employee in an EMPLOYMENT relationship with) one ORGANIZATION, but be assigned to a POSITION that is defined by a different ORGANIZATION. There is nothing wrong with this people are often temporarily assigned to departments other than the ones they officially work for but it is important to understand that this may happen.
    When a manager queries a data warehouse to ask "How many people work for my department?", if the answer is "42", that manager must understand whether that is 42 people who are each an employee in an EMPLOYMENT with the department, or 42 people who each hold a POSITION ASSIGNMENT to a POSITION defined by the department. The difference could be substantial--and important.




    Figure 14: POSITION