Re: The wisdom of the object mentors (Was: Searching OO Associations with RDBMS Persistence Models)

From: Sasa <sasa555_at_gmail.com>
Date: Sat, 03 Jun 2006 12:05:08 +0200
Message-ID: <e5rms9$ri0$1_at_sunce.iskon.hr>

mAsterdam wrote:

>>> Sasa wrote:
>>>
>>>> Marshall wrote:
>>>>
>>>>> There is a fundamental, foundational concept to grasp here,
>>>>> that is easily obscured by the excessive verbiage. But
>>>>> unless you get this foundational point, you won't be able
>>>>> to follow the arguments of the c.d.t. people at all. So I'll
>>>>> simply present it in isolation.
>>>>>
>>>>>   A DBMS is not "storage." A DBMS is a system that manages
>>>>>   data, where "manages" describes a whole host of high level
>>>>>   facilities.
>>>>
>>>>
>>>> So can you list some short but specific keypoints - what are these 
>>>> facilities?

>
>
> mAsterdam replied:
>

>>> One key facility would be the /sharing/ of data;
>>> between instances of applications (persistence can be
>>> viewed as a specific case of this: sharing between
>>> subsequent incarnations/runs), but also between different
>>> applications. 

>
>

>> No one ever disputed that (well at least, I didn't dispute it), 

>
>
> I did not say or think that you /did/ dispute that.

I didn't say you said it :-) I used the statement as a drammatical entrance to the subject :-)

> Aside: You snipped away your question.
> I repaired the damage, but I do not enjoy doing that.
> Please don't oversnip.

Sorry, to my mind your answer was standalone and I didn't see the substantial need for the original question to be repeated.

>> but is this simply not the consequence of persistance?

>
>
> How?
>

>> I mean - flat files offer this facility as well.

>
>
> You can share your data by putting bytes into files and send the file
> to the ones you want to share the data with (or put the file on
> a networked filesystem). Don't forget to instruct the other parties
> how to interpret the bytes in the file.

The same holds for RDBMS. If it's not available via network or at the client's site it is unavailable. The client still must be instructed in the structure of the database.

Granted though, RDBMS are standard whereas flat files are proprietary so it is much easier to reverse engineer a database (if no manual is available).

>> Now, I am very well aware that RDBMSes are much more powerful than 
>> flat files, 

>
>
> Agreed. Your other statements makes me wonder, though:
> In what sense are they more powerful in your view?

Normalization, querying, security, integrity, reliability, concurency, atomicity etc. come to mind

>> but in my current view - I regard both primarily as a persistence from 
>> my OO biased perspective. Why do I usually choose RDBMS over flat 
>> file? Because of this great features you and other have mentioned.
>> Do I treat then RDBMS as a flat file? Most certainly not - I have a 
>> isolation layer which decouples my OO code from my RDBMS code. Behind 
>> that layer I can fully leverage the power of RDBMS. 

>
>
> That seems like a sensible design heuristic for many applications.
>
> > From the client side I'm not aware of RDBMS existence.
>
> If you would have said "The application user does not
> for day-to-day use of the application need to be aware
> of the existence of the DBMS" I could agree.
> Is that what you meant?

Not really - the OO code which uses database is not aware of the specific implementation.

>> When analysing or debugging the data I most certainly use the query 
>> editor and write ad hoc queries to find out what interests me.

>
>
> Do you also relax the isolation requirement for user ad hoc queries?

What kind of app would it be i.e. for what kind of users? I consider SQL statements other than simplest ones to be fairly inappropriate for the non programmer user.

>> I worked on a legacy app which used proprietary flat files for 
>> persistence. It was a nightmare when I had to analyze what's in there.
>>
>> So no, I don't think I'm fully underestimating the power of the dark 
>> side :-) Sorry just couldn't resist - no harm meant there, I meant the 
>> power of the RDBMSes. I am open to the possibility that RDBMSes can be 
>> ever more used than I am currently using them, and are much more 
>> appropriate for some stuff I currently do in OO. But to accept this 
>> notion I would need more specific details on your preferred approaches.
>>
>>> Why not? Simply serializing/deserializing all objects
>>> (like smalltalk did - the "system image")
>>> to a file on secure media gives you perfect persistence.
>>> That you want more shows that you already are
>>> aware of some desiderata beyond just that.
>>
>>
>> Well to me, most of these other features are rather "persistence 
>> related".

>
>
> Sharing data can be persistence related.
> Naked persistence only gives you very clumsy ways of sharing.
>
> Please give some specifics regarding "these other features".

If I regard entire DBMS as a persistence than all of its features (querying, security, reliability etc.) are obviously persistence related.

>

>>>> Given the fact the DBMS can serve more apps (but actually even one 
>>>> can mean trouble if SQL code is spread around the app code), and 
>>>> given the fact that one app might want to switch DBMSes I think it 
>>>> would be smart to decouple both as much as possible, which to me 
>>>> means no client code in DBMS, and very localized DBMS specific 
>>>> statements in client code. Now 
>>>
>>>
>>>
>>> "no client code in DBMS" - could you give an example of what you'ld 
>>> consider typical client code?
>>
>>
>>
>> As can be seen from my other posts, I write my domain logic (the core 
>> business data and behavior) in OO and use RDBMS for persistence. 

>
>
> Don't. If persistence is all you need, a DBMS is
> terrible overkill. How do you justify the additional
> investment (not talking licenses, but mainly the creation
> and maintenance of the staff's DBMS skills)?

Most businesses want to have their data at their own network, so the DBMS existence and supporting staff is usually inherently there.

Other than that, the features listed above should support the cause. But ...

>> The data is hence in the database only because it must persist. 

>
>
> A secure, backed-up filesytem will do nicely for persistence only.

... it depends on the case (the specific app being developed).

>> Moving the behavior to the DBMS would mean moving   client code (the 
>> non DBMS code which somehow directly  or indirectly uses the database) 
>> to the database.
>>
>> I was working on a financial application once, where a lot of such 
>> logic was implemented in the SQL database. There was number of large 
>> stored procedures which performed complex financial calculations. The 
>> code looked horribly - with lot of verbose, bulky IF THEN ELSE blocks, 
>> etc. it reminded me more of my BASIC days than of the professional code.
>>
>> In addition, the app was being distributed to different clients. 
>> Between any two clients some subset of the calculation algorithm 
>> varied to some degree, with most of the logic being the same.
>>
>> This was being resolve by simply switching the stored procedures code 
>> - for each client we had the SPs scripted. The structure being used 
>> (tables) was the same.

>
>
> So, you had some server-side, customer specific code
> (I say customer here to disambiguate from client as in client/server
> architecture). You did provide your customer with the schema DDL
> in the distribution package, didn't you?

Yes, where we were the customers (in your dictionary). The end user would receive entire app (client code and database). There were multiple end users. So I think you misunderstood me a little (or I didn't describe it accurately).

>> So if we wanted to work on an app for another clients, we would 
>> execute appropriate scripts which would then regenerate SPs and then 
>> we would have the appropriate code. Needless to say, there was fair 
>> amount of duplication (or rather n-plication) with slight variations 
>> in some places.

>
>
> Customer specific issues at the client-side have to be
> resolved as well. I don't see a fundamental difference.

Now I don't understand this statement. In this passage I was pointing out the duplication problem.

>> To summarize - there are two problems:
>> 1. Complex ifological sequential logic

>
>
> Please elaborate.

Caculating algorithm consists of many sequential steps, after almost any step if else if ... branch occurs, as the algorithm (as defined by end users in their financial domain) is complex per se.

> BTW: Where was this in what you are summarizing?

In the "lot of verbose, bulky IF THEN ELSE blocks" but very poorly elaborated. Hope this previous paragraph sheds some better light.

>> 2. Code reuse which supports variations on appropriate places

>
>
> There may be customer specific code on both client and server.
> You either prevent that or you don't. How does this relate to
> persistence?

This statement again I don't understand. The problem I was referring to is that end users use the same app (visually) with same business entities, and almost the same business rules (in this case financial calculations).
How do you promote maximal reuse via DBMS?

>> Now, I have fairly good idea how to resolve these in OO, but have no 
>> idea how do you deal with such issues in DBMSes. Simply, when it comes 
>> down to the behavioral, sequential code, and as far as I know it has 
>> to come down to it sooner or later, I regard OO as a better choice.

>
>
> IMO There is no choice here.
> There is just appropriateness of metaphors and discipline.
> Pretending there is a choice here culminates in a
> counterproductive us vs. them attitude.

What do you mean? There is a choice as there are multiple paradigms, languages, technologies and tools available to solve the problem. You have to select which ones will you use and distribute the responsibility to each one selected. Is that not the act of choosing? Given the fact that there are multiple possibilities isn't one faced with a choice?

>> Disclaimer: I can agree that the example just presented was simply bad 
>> implementation (it most certainly was).

>
>
> Let's talk about good implementations :-)

That's what I want to hear. How do you envision the role of DBMS?

>>>> I'm interested with what part you DBMS guys (no irony, or offense 
>>>> meant) disagree and how do you envision it?
>>>
>>>
>>>
>>> I'm not fond of the us vs. them approach - but I am a c.d.t. regular.
>>
>>
>>
>> Well I'm obviously on the OO side, but would like to hear some 
>> specifics from the cdt guys, to expand my horizons, learn something 
>> new, shift my way of thinking etc.
>>
>> Do you think OOLs are inferior to RDBMSes in all aspects,
>> and if so are they redundant? 

>
>
> No I don't.

Great (would be also great if you had answered with a yes)! What are then in you view strengths of OO, when is it appropriate and when not?
The same question for RDBMS.
How do you divide responsibilities between two if they are used in the same system?

>> If yes, of what parts (with respect to languages) should a typicall 
>> application consist? 

>
>
> That is to big a question to answer.
> IBM abandonded the SAA (standard application
> architecture, early 90's) when they found out.
> You are not the first to ask.
>
> For the non-sequential infological approach I like ORM,
> for c.o.: that is Object Role Modeling, http://www.orm.net/
> not Object-Relational-Mapping which IMO is a non-issue,
> stemming from the OO-side of the destructive us vs.
> them attitudes. If you care to investigate:
> don't be confused by the graphics.

Thanks for the tip, will certainly investigate.

>> Do you apply such approaches in your apps and how does it works for you?

>
>
> Yes. Not everywhere (appropriateness!).
>

Sasa Received on Sat Jun 03 2006 - 12:05:08 CEST