Hi one and all,

This is a general question, related to the theoretical organization of OOP and CB.

Not being in the centre of the Coding community this may seem an odd question but I am not sure of the distinctions between USER Services, BUSINESS Services and Data services.

By way of example....

USER or BUSINESS

In the CB world Is a Combobox in a bizobj Proper to a user service or a Business Service. If this same cbo is directly in a formobj is its theoretical classification different.

BUSINESS or USER

Are CB's BizObjs BUSINESS services or USER services as they are the interface between the underlying data and the user.

Should Classes like "MySpecialProxyListBox" be classified as a User Class or a Business class as it would presumably be the interface to the user but located in a bizobj.

BUSINESS or DATA

As business object undertake the creation and saving of the views data in CB are they Data services or Business services.

This may seem "OLD Hat to many of you but I am playing "Catchup"

Thanks in advance to all you theoreticians

Geof Whitham

Penang,Malaysia

<b>User Services</b>... basically, UI controls and coding that is responsible for interacting with the user. Things such as presenting data, accepting input, showing messages to the user, etc. (cForms.vcx, cControls, etc.)

<b>Business Services...</b> this entails classes and code the is reponsible for defining business domian rules... Things like, If a customers credit rating is 4 they can order up to $5,000 per month on credit. Or, this may be code that posts GL transactions. (Business objects, generally, there are still some UI stuff in CB bizobjects. Also, there is no current way in CB to physically seperate the User and Business tiers.)

<b>Data Services...</b>... this is generaly the physical manipulation of the data and the integraty thereof seperate from the bizrules. Handels saves, generating keys, cascade deletes, audit trails, etc. (This is generally a combination of the data behavior objects and the VFP data engine (.DBC definitions) or SQL server or other basckend you are using.)

BOb

BOb

<I><FONT COLOR="#663300">Not being in the centre of the Coding community this may seem an odd question but I am not sure of the distinctions between USER Services, BUSINESS Services and Data services.</FONT></I>

I see that Bob has already given you a good explanation of the different services, or tiers, in Codebook.

<I><FONT COLOR="#663300">USER or BUSINESS

In the CB world Is a Combobox in a bizobj Proper to a user service or a Business Service. If this same cbo is directly in a formobj is its theoretical classification different.</FONT></I>

This is one of the problems with Codebook as it originally existed: it mixed the elements of the presentation layer and the business layer. Its examples included bizobjs with contained controls; even the choice of basing the cBizobj class on the VFP base class of "Container" instead of "Custom" reflects this design.

The important thing to remember is that there is absolutely nothing in Codebook which <I>requires</I> that you mix the two. I have created many apps with non-visual bizobjs, and they work perfectly well.

<I><FONT COLOR="#663300">BUSINESS or DATA

As business object undertake the creation and saving of the views data in CB are they Data services or Business services.</FONT></I>

They are business services, but the actual saving, requerying and opening of views does not take place in the bizobj, but rather in the DataBehavior object to which the bizobj has a reference. That way if you ever wanted to work with a data source which did not lend itself to VFP views, you could write a new DataBehavior class to handle the translation, and the bizobjs would work without change.

<font color="#cc0000"> ___/

/

__/

/

____/</font>

Ed Leafe

Okay so I am thick, but does the Polymorphism donkey upset Inheritance cart?

Using an example from a book to explain Poly...

*****

DEFINE CLASS xPoly AS custom

PROC show

WAIT WINDOW 'This is the root class'

ENDPROC

ENDDEFINE

DEFINE CLASS xPolyChild AS xPoly

PROC show

? 'This is the child of xPoly'

ENDPROC

ENDDEFINE

SET PROC TO ...

oTest = CREATEOBJECT('xPolyChild')

oTest.Show()

****

Only shows the child not the parent, unless I included DODEFAULT() in

xPolyChild.Show

Is this correct, it does make sense?

regards

Stuart Hurley

ams_ltd@dial.pipex.com

Makes sense to me, because without the dodefault(), your child proc (Show) is

overriding the inherited code.

HTH,

--Mike

>>> "computing@dial.pipex.com" 09/14/99 09:37am >>>

####################################################

The following message part was sent with the unknown

character set: "WINDOWS-1252"

####################################################

Okay so I am thick, but does the Polymorphism donkey upset Inheritance cart?

Using an example from a book to explain Poly...

*****

DEFINE CLASS xPoly AS custom

PROC show

WAIT WINDOW 'This is the root class'

ENDPROC

ENDDEFINE

DEFINE CLASS xPolyChild AS xPoly

PROC show

? 'This is the child of xPoly'

ENDPROC

ENDDEFINE

SET PROC TO ...

oTest = CREATEOBJECT('xPolyChild')

oTest.Show()

****

Only shows the child not the parent, unless I included DODEFAULT() in

xPolyChild.Show

Is this correct, it does make sense?

regards

Stuart Hurley

ams_ltd@dial.pipex.com

********************************

Michael Babcock

KePRO, Inc.

Tel: 717-564-8288

Fax: 717-564-4188

Internet Address: mbabcock@kepro.org

Home Page: http://www.kepro.org

********************************

You got it exactly right Stuart.

The beauty of subclassing and VFP is that you can completely override the

behavior of a method in a subclass and the class interface doesn't change.

A better design may have been to have an AbstractPoly class which has just an

Empty Show method() and then subclass into PolyWaitWindow and PolyPrint

AbstractPoly Show method does nothing

PolyWaitWindow Show method shows stuff via WAIT WINDOW

PolyPrint Show method show stuff via ?

Although the implementation of the Show method in each subclass is different,

the interface into the object remains the same in all classes. So if I want to

write a program which initially does wait windows I can do

At design time or in a separate program/class I can do

this.cPolyClassToInstatiate = 'PolyWaitWindow'

In a standard program used regardless of the actual implementation of the Show()

method

loPoly = CREATE(this.cPolyClassToInstatiate)

loPoly.Show()

And then later, if I change my mind, I just have to change the calling

program/class to do

this.cPolyClassToInstatiate = 'PolyPrint'

"AMS Computing" <computing@dial.pipex.com> on 09/14/99 09:22:58 AM

Please respond to profox@leafe.com

To: Multiple recipients of ProFox <profox@leafe.com>

cc: (bcc: Mary Hintermeier/RSA)

Subject: VFP6 & OOP - newbie question

Okay so I am thick, but does the Polymorphism donkey upset Inheritance cart?

Using an example from a book to explain Poly...

*****

DEFINE CLASS xPoly AS custom

PROC show

WAIT WINDOW 'This is the root class'

ENDPROC

ENDDEFINE

DEFINE CLASS xPolyChild AS xPoly

PROC show

? 'This is the child of xPoly'

ENDPROC

ENDDEFINE

SET PROC TO ...

oTest = CREATEOBJECT('xPolyChild')

oTest.Show()

****

Only shows the child not the parent, unless I included DODEFAULT() in

xPolyChild.Show

Is this correct, it does make sense?

regards

Stuart Hurley

ams_ltd@dial.pipex.com

Stuart,

This is correct. You are overriding xPoly.Show() with xPolyChild.Show(),

not appending to it. The DoDefault() makes an explicit call to the Parent

method of the same name. This gives you the ability to add code before

and/or after the parent code or, as you have demonstrated, override the

parent code. Sample of before and after:

Proc Show

Wait Window 'This is Child Before Parent'

DoDefault()

Wait Window 'This is Child After Parent'

EndProc

HTH

Chad Bourque

U.S. Bankruptcy Court - 11th Circuit

Alabama - Northern District - Southern Division

Chad@teche.net

----- Original Message -----

From: AMS Computing <computing@dial.pipex.com>

To: Multiple recipients of ProFox <profox@leafe.com>

Sent: Tuesday, September 14, 1999 8:22 AM

Subject: VFP6 & OOP - newbie question

: Okay so I am thick, but does the Polymorphism donkey upset Inheritance

cart?

:

: Using an example from a book to explain Poly...

:

: *****

: DEFINE CLASS xPoly AS custom

: PROC show

: WAIT WINDOW 'This is the root class'

: ENDPROC

: ENDDEFINE

:

: DEFINE CLASS xPolyChild AS xPoly

: PROC show

: ? 'This is the child of xPoly'

: ENDPROC

: ENDDEFINE

:

: SET PROC TO ...

: oTest = CREATEOBJECT('xPolyChild')

: oTest.Show()

: ****

:

: Only shows the child not the parent, unless I included DODEFAULT() in

: xPolyChild.Show

: Is this correct, it does make sense?

:

: regards

:

: Stuart Hurley

: ams_ltd@dial.pipex.com

:

:

:

"Is this correct, it does make sense?"

Seems OK to me too, but I'm not very OOPy.

BTW if you do DODEFAULT() you then get :

1) a ? message

2) a wait window

both generated by your SHOW() - thus exhibiting a simple polymorphism in

the SHOW method.

That's how VFP works. Userdefined code is always overridden unless the

superclass code is called with :: or dodefault(). Baseclass behavior is

never overridden unless stopped with NODEFAULT. Other OOP implementations

work the other way around. There's no one right way.

-Anders

----- Original Message -----

From: AMS Computing <computing@dial.pipex.com>

To: Multiple recipients of ProFox <profox@leafe.com>

Sent: tisdag den 14 september 1999 15:22

Subject: VFP6 & OOP - newbie question

| Okay so I am thick, but does the Polymorphism donkey upset Inheritance

cart?

|

| Using an example from a book to explain Poly...

|

| *****

| DEFINE CLASS xPoly AS custom

| PROC show

| WAIT WINDOW 'This is the root class'

| ENDPROC

| ENDDEFINE

|

| DEFINE CLASS xPolyChild AS xPoly

| PROC show

| ? 'This is the child of xPoly'

| ENDPROC

| ENDDEFINE

|

| SET PROC TO ...

| oTest = CREATEOBJECT('xPolyChild')

| oTest.Show()

| ****

|

| Only shows the child not the parent, unless I included DODEFAULT() in

| xPolyChild.Show

| Is this correct, it does make sense?

|

| regards

|

| Stuart Hurley

| ams_ltd@dial.pipex.com

|

|

|

Jerry

Nodefault doesn't prevent the parentclass from running, it prevents the

baseclass behavior from doing its stuff.

-Anders

----- Original Message -----

From: Cotton Jerry P <CottonJP@2mawcp.usmc.mil>

To: Multiple recipients of ProFox <profox@leafe.com>

Sent: tisdag den 14 september 1999 18:55

Subject: RE: VFP6 & OOP - newbie question

| As I understand inheritance (if I'm confused somebody straighten me out)

|

| When you put code in the child property you are overriding the code that

is

| in the parent class, thus the behavior that you note. DODEFAULT()

| explicitly calls the code of the parent class just as NODEFAULT explicitly

| prevents the parent code from running.

|

| The following shows both statements.

|

| oTest = CREATEOBJECT('xPolyChild')

| oTest.Show()

| DEFINE CLASS xPoly AS custom

| PROC show

| WAIT WINDOW 'This is the root class'

| ENDPROC

| ENDDEFINE

|

| DEFINE CLASS xPolyChild AS xPoly

| PROC init

| ? 'This is the child of xPoly'

| ENDPROC

| ENDDEFINE

|

| Mr. Jerry Cotton MCP

| 2nd Marine Aircraft Wing Comptroller's Office

| MCAS Cherry Point NC

| mailto:cottonjp@2mawcp.usmc.mil

| (252)466-2320 fax (252)466-4806 DSN-582

|

|

| -----Original Message-----

| From: AMS Computing [mailto:computing@dial.pipex.com]

| Sent: Tuesday, September 14, 1999 9:23 AM

| To: Multiple recipients of ProFox

| Subject: VFP6 & OOP - newbie question

|

|

| Okay so I am thick, but does the Polymorphism donkey upset Inheritance

cart?

|

| Using an example from a book to explain Poly...

|

| *****

| DEFINE CLASS xPoly AS custom

| PROC show

| WAIT WINDOW 'This is the root class'

| ENDPROC

| ENDDEFINE

|

| DEFINE CLASS xPolyChild AS xPoly

| PROC show

| ? 'This is the child of xPoly'

| ENDPROC

| ENDDEFINE

|

| SET PROC TO ...

| oTest = CREATEOBJECT('xPolyChild')

| oTest.Show()

| ****

|

| Only shows the child not the parent, unless I included DODEFAULT() in

| xPolyChild.Show

| Is this correct, it does make sense?

|

| regards

|

| Stuart Hurley

| ams_ltd@dial.pipex.com

|

|

|

|

|