- Most real world problems have LOTS and LOTS of entities, so the second step is to:
figure out which ones matter.
- You might eliminate ITEMS for any one of FOUR MAJOR REASONS:
a. They’re already covered
b. They’re too specific
c. They’re just attributes of another entity.
d. They’re not important enough to track.
- After thinking about each ENTITY on the list, you can:
REMOVE AND POSSIBLY add some new ones. When you’re through with this step, you have a pretty GOOD LIST OF ENTITIES-and TABLES- in your database.
- What do Relationships tell FM?
RELATIONSHIPS TELL FILEMAKER WHICH RECORDS IN TWO TABLES GO TOGETHER.
- Conceptually, RELATIONSHIPS come in three flavors:
a. ONE TO MANY
b. MANY TO MANY
c. ONE TO ONE
- In a ONE TO MANY RELATIONSHIP, one record in one table relates to:
SEVERAL records in the second. One INVOICE RECORD has SEVERAL LINE ITEMS, so it is a ONE TO MANY.
- Similarly, SEVERAL LINE ITEMS BELONG TO ONE INVOICE, so it s a MANY TO ONE RELATIONSHIP. Since RELATIONSHIPS WORK BOTH WAYS:
a ONE TO MANY IS ALWAYS A MANY TO ONE.
- Explain a MANY TO MANY RELATIONSHIP
You have a PRODUCTS TABLE and an ORDERS TABLE. They have a MANY TO MANY RELATIONSHIP: a PERSON ORDERS MULTIPLE PRODUCTS, AND EACH PRODUCT CAN BE ORDERED MANY TIMES (by different people?)
- Explain a ONE TO ONE RELATIONSHIP
If your database holds pictures of each item you sell, you could create a PICTURES TABLE, and each PRODUCT RECORD on the PRODUCT TABLE is related to exactly ONE PICTURE RECORD in the PICTURE TABLE.
