The User and Message Database Relationship

It might be helpful at this point to illustrate the way the user and message databases work together. Figure 4.6 shows the relationship between user and message databases.

Figure 4.6. The connection between user and message databases

In the example shown in Figure 4.6, the user assigned to USER123.DB has sent a message to another user. USER123.DB is assigned to send through MSG17.DB, and has sent to USERABC.DB. The following numbered items correspond to the numbered arrows in Figure 4.6:

1. In the USER123.DB file, there is a record for a sent item. This record has a pointer to the message item record in MSG17.DB.

2. In MSG17.DB, there is an item record that was created by USER123. This item contains an attachment that is larger than 2048 bytes, so that attachment data is written to a BLOB file. The item record contains a pointer to this BLOB file in the OFFILES directory structure.

3. In USERABC.DB, there is a record for the item received from USER123. This record contains a pointer to the message item record in MSG17.

From this simplified illustration, you can see that even if a dozen users on a post office have a copy of a message in their inbox, that message record exists only once in the appropriate message database. An attachment sent to several people is written to only one BLOB file.