> 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. * To join/leave the list, search archives, change list settings, * * etc., please visit http://raven.utc.edu/archives/hp3000-l.html *