> A relational database is a collection of data items organized as a set
> of tables from which data can be accessed or reassembled in many
> different ways without having to reorganize the database tables.

The term relational comes from relational mathematics, i.e. set theory. This
is why there are union and intersection (join) functions.

> Eloquence from my understanding is built upon B-tree structures.  To
> access the data, the engine has to navigate the tree structure of key
> values.

I was corrected by Fred White once: There are no such things as relational,
network or hierarchical databases. There is only relational, network and
hierarchical access.

> This is what is known as a hierarchical database structure, which is
> what IMAGE is.

In a hierarchical database, a child set can only have one parent. In a network
database, the children can have multiple parents.

Image is a "simple network" database. Its children can have multiple parents
but can't be parents to other children which is possible in a full network
database like IDMS.

> RDBMS have become more prevalent due to several facts, one big one
> already mentioned is SQL.  The other is flexibility.

ImageSQL *is* an SQL interface for Image, so Adam's point stands that having
an SQL interface does not a relational database make.

> Doing something like adding a field in a hierarchical database can force
> changes across the entire application.  Which is typically not the case
> with a relational database.

I assume you mean that one can cascade updates/deletes? This is not built into
Image but it certainly could have been, especially with the advent of Critical
Item Update.

> Some shops are willing to live with the limitations because Retrieving
> data from Hierarchical databases is historically faster due to the same
> organizational structure that limits the flexibility.

True.

Mark W.

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