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Hi Dieter

I must admit that I've never understood when people say that DB2 on IBM i is not relational. Then they will say it is ISAM, as if that is not relational.

I do not say that this is exactly what you are saying. But I do hear you say that ISAM is to be used only for small tables.

So I went looking for more about ISAM - there is a Wikipedia article on this at

Here is one use of the term ISAM as this article puts it - the article lists 4 ways people use the term these days, which might not be the strict, original meaning, I suppose.

"An indexing algorithm that allows both sequential and keyed access to data.^[3] <https://en.wikipedia.org/wiki/ISAM#cite_note-3> Most databases use some variation of the B-Tree <https://en.wikipedia.org/wiki/B-Tree> for this purpose, although the original IBM ISAM and VSAM <https://en.wikipedia.org/wiki/VSAM> implementations did not do so."

I believe that IBM Rochester say that B-Tree (or some variation) is the indexing methodology used for indexing on IBM i - the above statement feels familiar and also relates to RLA in RPG and COBOL and the like. I saw also that there are ISAM APIs that provide ways to get to data in an ISAM setup. Do we mean like CHAIN, READ, READE, etc.? And C/C++ on IBM i has equivalents to those, and an even more complete set of functions to provide record-level access.

The same article makes this assertion - "Relational databases <https://en.wikipedia.org/wiki/Relational_database_management_system> can easily be built on an ISAM framework with the addition of logic to maintain the validity of the links between the tables. "

That statement suggests something I've felt all along - that the terms "relational database" and "ISAM" are at different levels - an RDBMS can be built over any of several database frameworks, with, I suspect, varying levels of difficulty in that implementation. ISAM is one of those several frameworks.

So I suggest that statements that seem to say that an underlying framework that is ISAM does not mean we don't have an RDBMS there. PC Magazine, for example, has this as the definition of "System/38" - "A minicomputer from IBM that included an operating system with an integrated relational database management system."

I don't know that my thoughts here are an answer to a question that wasn't asked, or if it rebuts anything said - I just present the thoughts for consideration.

I do believe that we do have an ISAM framework and an RDBMS over it. Any distinctions of those 2 concepts, these 2 different levels of abstraction, are not very important, to my way of thinking.

Cheers
Vern

On 1/13/2017 2:02 AM, D*B wrote:
RPG would be my preference on IBM i. But what if your DBMS is Oracle or MS
SQL Server? Developers might use SQL stored procedures, which do run in the
same address space as the DBMS although my point about "direct access" is
debatable. I'm not sure if Oracle and MS SQL Server provide RLA in addition
to SQL.

.. what you are naming direct access is ISAM and was developed in the 1960s, before relational DBMS came up. DB2/400 is the only DB2 dialect providing ISAM, IBM Host (/360, /370, z-series) has ISAM and VSAM for this, DB2 is only accessable by SQL. Unix has Informix and C-ISAM. Good practice is to use ISAM only for small Tables for large Tables and high transaction throughput RDBMS and SQL is faster and scales better.

@business logic - business rules: maybe my knowledge of enhlish language is not good enough, in my understanding business logic implements the business rules (what else should it do?)

D*B


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