Throwback: Today's Empire of Invent3K
Sharing the Source of SLEEPER for MPE

Manual and Automatic Masters, Detailed

A few days ago we included a Hidden Value question about how manual and automatic masters work in TurboIMAGE. Our ally and friend Vladimir Volokh called to note that in part of the question, the system manager had found "one detail data set that has thousands of entries which do not appear to be connected to any master.

It wasn't exactly a question, but in a reply on the 3000-L mailing list and newsgroup, Roy Brown gave a fine tutorial on how these features do their jobs for MPE and the 3000 -- as well as how a detail dataset might have zero key fields.

Manual masters can contain data which you define, like Detail sets can, along with a single Key field. Automatic masters contain only the Key field.

In both cases, there can be only one record for a given key value in a Master dataset.

A Detail dataset contains data fields plus zero, one, or many key fields. There can be as many records as you like for a given key value, and these form a chain accessible from the Master record key value. This chain may be sorted, or it may just be in chronological order of adding the records.

Zero key fields in a Detail dataset would be unusual, but is permissible.

Brown explained that "Where there are keys, referential integrity demands that there are no Detail record entries with a key field that is not found in either a Manual or Automatic master, both Key name and Key value. So a Detail data set with Key fields that are not present in a Master record would be a sign of a seriously corrupted database."

However, I doubt this is the case, and when you do a QUERY FORM command, you will see which fields in Detail datasets are Keys, which fields are used to establish Sort orders, and which fields are data pure and simple.

From the Key name, you can determine which Master set links the keys.

As I said above, it is possible to have a Detail dataset with no keys, but these usually contain only a very few records, since direct access to them without keys is cumbersome, and you would otherwise have to trawl right through one to find any given entry.

So a Detail dataset with thousands of unconnected entries would be very unlikely.

The FORM output will allow you to check how the Detail dataset that you think might have unconnected entries is actually linked in.