TABLE OF CONTENTS The messages exchanged between the system and its environment are about the subject domain. The descriptions of the system purpose and responsibilities, and of the desired system services, also refer to the subject domain. To understand the meaning of these descriptions, it is useful to describe the subject domain in more detail.
Chapter 8. I introduce entity-relationship diagrams (ERDs) as a notation to describe which types of entities can exist in the subject domain and how many of them can exist.
Chapter 9. I give guidelines for finding an ERD of the subject domain.
Chapter 10. I show how to write dictionary entries. The meaning of key terms in the mission statement and service descriptions should be understood by both the customer and designer. Many of the key terms in these descriptions refer to the subject domain; therefore, I include the chapter on writing dictionary entries in this part. Note, however, that the dictionary contains more terms than just subject domain terms and that not all subject domain terms need be included in the dictionary because they are already described elsewhere. For example, the technical documentation of devices may already define important terms. My second reason for including the chapter on writing dictionary entries in this part is that definition by genus and difference (treated in Chapter 10) corresponds closely to defining taxonomic subject domain structures (see Chapter 9).
We use an entity-relationship diagram (ERD) to represent...
