Everybody’s talking about data-centric programming. Well, I mean you won’t hear people talking about it in a bar or anywhere fun, but whatever. But this isn’t a bar, is it? No, more’s the pity. So, since there’s nothing else to do, let’s talk.
Written by David Shirey
A few months ago, I wrote an article about data-centric programming. And it was very nice and all, but I want to get specific and cover a fair amount of detail about how to actually go about it.
What Is Data-Centric Programming?
I think the first thing we should do is remind ourselves just what data-centric programming is. In short, it means using a database-based language to do your work instead of a more standard procedural language like RPG.
In order to be useful, this data-centric language must consist of not only the data access and update procedures that we are used to with embedded SQL, but also conditional, looping, and other control-type statements required by a “real” language. If it does, then it can really and truly compete with RPG.
Many data-centric languages are out there, but for the i world, that would be the Programming Language (PL) that is part of DB2.
I guess the first question we need to answer, or at least review from the previous article, is why you want to bother.
After all, we have RPG, and we can do everything we need in there. And if you want to use DB2 instead of the DDS files, you can do that with embedded SQL in your RPG program.
I suppose there are a bunch of reasons, but the only one that really stands out to me is you would do this because you want to free yourself (and your applications) from a language that struggles mightily not to look archaic. By abandoning RPG in favor of a data-centric language, you are eliminating the need to find RPG programmers and removing the specter of languages past from your system. DB2/SQL is a “modern” language the way everyone views things, and it is something that almost all new programmers understand. I have to admit, I have problems with this because I am an RPG guy and especially an RPG free-format guy, but SQL is everywhere, and if I need new talent, I don’t have to look for someone who knows RPG, just someone who knows SQL.
What Is PL?
As I said above, the language we will look at is the DB2 Programming Language (PL), and it comes standard on your i as part of DB2. Yeah, something you don’t have to buy!
It is based in the same SQL that we could embed in RPG, but it goes further and special functions have been added that allow it to do decision-making, iterations, and other activities that separate a fully functional language from the mere data access and update capabilities of SQL.
The one caveat is that PL has no capability to display data the way RPG does, although most people aren’t interested in showing data the way RPG does anymore. In both cases, you would involve some other language to do the web display of the data accessed and manipulated.
Bottom line: DB2 PL is a viable alternative to traditional RPG and may be something you want to investigate more. To do so, we are going to spend some time figuring out how it works and how to get it off the ground.
What Does It Look Like?
I know that, when I am looking at a new language, the first thing I want to know is what it “looks like.” Not what it can do or even how finicky it is, but what it looks like. With languages, as with people, we draw certain conclusions right off the bat based on looks. Is it structured in any way, can it be read like English, does its syntax look “normal” to me?
Since it’s origins are DB2, it looks a lot like SQL. That is, we have the standard SQL-type commands: Insert, Fetch, etc. But there are also other commands too because, for it to be a functioning language, we need to be able to do control statements (IF-THEN, WHEN), loops (LOOP, FOR, WHILE, REPEAT), and basic set-equal-to logic (SET). But all that shall be revealed in its proper time.
Where to Store Them
So how do you get started with PL? Well, the first element is to figure out how you are going to set up the scripts. We are used to a world where all programs belong to some source file (QRPGLESRC, QCLSRC, etc.) in the i.
There is no preset source file where your PL scripts will reside, so you have to create one with the CRTSRCF command.
What you name it is up to you. I set mine up as QPLSRC. That bothers me in a way because I like to have three characters after the Q and before the SRC, but sometimes you have to just deal with things. At least I can tell that these are PL scripts. Of course, you could just dump them into any existing source file, but that is way too untidy for me.
What is important is that, when you create the scripts, you create them with a source type of SQL. And don’t think you can use RPGSQL or RPGSQLLE as the type. Those are for RPG programs with embedded SQL, and that is not what we are doing.
That’s All, Folks
And I am afraid that is all for this month. In our next tip, we will actually create a working PL script, compile it, and run the dang thing. Can’t wait. See you then.