OOD/OOP and databases

[Thomas Jespersen]

Hello

I've been reading a lot of great OOD/OOP books lately (e.g.. Martin Fowlers
UML Distilled, Patterns of Enterprise Application Architecture, Refactoring,
Kent Becks's Test Driven Development, and also a book called Design Patterns
Explained.)... al of them with the focus on Java, because I think the best
books are targeted Java. But the all fit very well to the .NET platform.

I have one big problem when reading these great books, and that is that they
focus almost entirely on the Domain Model (that is the Middle Layer in a 3
layered architecture). They hardly mention that the code you write is to be
used in a UI interface and committed to a database ([PoEAA] might be an
exception). I find the separation of Business Login and UI to be the hardest
thing. And also I find the performance issues when talking to the Database
to a very tricky thing, that calls for a few hack in the Domain Layer (I'm
almost only doing thick clients... that is no web).

So I would like to know how you OO Guys really work (references to books or
articles would be great).

Don't you design your database the same way that you design you Business
Model if you are responsible for all 3 layers/tiers?

How much time does you spend on writing the DAL (the mapping between the OO
and the Database)? Do you use any kind of O/R Mappers to help you write the
DAL?

Where do you place the tiers in a Smart Client configuration? The way I see
it the UI and Domain Model must be on the client. Because you Domain Model
contains a lot of information e.g. about validation the input, and I don't
want a Server Round Trip every time the users enters something in a textbox.
But I'm also thinking about putting the same domain objects on the server
aswell and use some kind of serialization using .NET Remoting or Web
Services. Anyone else placing the Domain Model on both the Client and
Server?

Can you recommend any third party frameworks, which addresses any of these
problems? I find many of the MS Reference application to be to exotic.

I know these are big questions for a thread in a newsgroup... but never the
less, I haven't found any books or articles that really deals with these
issues.

Best regards,
Thomas
MCSD, MCSE+I, MCP+SB

 

[Nick Malik]

Yes... that's a lot for a newsgroup.

Start here:
http://www.microsoft.com/resources/practices/default.mspx

I, too, have read many of the same books. You didn't mention the Design
Patterns book itself (Gang of Four: Gamma, Helm, Johnson, and Vlissides) but
it, too, is an excellent volume. There are also a number of patterns books
that describe code in C# that have been coming out in the past two years.

The books do not focus on a particular tier. The Design Patterns books,
specifically, focus on a specific level of abstraction. The Fowler book
focuses on a different level of abstraction. Buschmann takes on the
architectural level. Honestly, to answer your questions, Buschmann is the
best of the group.

The Microsoft site has some very specific advice for the .NET platform with
regards to optimizations... worth looking into.

As for me: my middle tier is normally tailored to one thing: hiding the
business rules. That requires real analysis: what are the business rules...
what will change... how will they change... how will we maintain them.

Config files are not good for business rule changes... they are too
tactical. You can change the name of a stored proc in the config file. To
change the business rules, you need to encapsulate logic, not just
constants. Using pluggable components will only get you so far.

So, if the business layer has very few business rules, it's really thin.
For many purposes, especially for domain tables (lookup tables), I don't
have any logic at all in the middle tier. In that case, I often simply pass
the data through directly from the DAL to the UI layer as an array of
DataRows. I'll even occasionally bind directly to a control (not often, but
for drop-downs, it's good). On the other hand, if the business layer has
business rules to encapsulate, then I will organize the objects so that
managing those rules makes sense. This is where we start to deviate from
"business objects that mirror the database". This is where the design
patterns come in handy. You really have to map your data into objects that
isolate change and minimize complexity.

I've yet to find a tool or framework that does more than simply
copy-and-reflect operations from the database through the middle tier. I
don't use them. WHat a massive waste of time and processing power. Heck...
the DataSet object does a better job than most of these, and it doesn't
require a huge amount of effort to use! (I don't use it either... I'm just
making a point).

As for copying the validation rules: For a thick client app, I'd have the
same validation dll on both the client and the server. That way, you can
insure common rules. Note: business rules are much more than validation.
I'd have basic validation types that I can use in both places, but the rest
of the rules are quite different.

As for use of remoting: depends on the kind and style of scalability you
want to achieve. For my preference, remoting is too tightly coupled for the
kinds of things that I do... I tend toward web services... but that may not
be advice that you can use... depends on your app.

I hope this info is helpful.
--- Nick Malik
Application Architect
MCSD, CFPS, Certified Scrummaster

Hello

I've been reading a lot of great OOD/OOP books lately (e.g.. Martin Fowlers
UML Distilled, Patterns of Enterprise Application Architecture, Refactoring,
Kent Becks's Test Driven Development, and also a book called Design Patterns
Explained.)... al of them with the focus on Java, because I think the best
books are targeted Java. But the all fit very well to the .NET platform.

I have one big problem when reading these great books, and that is that they
focus almost entirely on the Domain Model (that is the Middle Layer in a 3
layered architecture). They hardly mention that the code you write is to be
used in a UI interface and committed to a database ([PoEAA] might be an
exception). I find the separation of Business Login and UI to be the hardest
thing. And also I find the performance issues when talking to the Database
to a very tricky thing, that calls for a few hack in the Domain Layer (I'm
almost only doing thick clients... that is no web).

So I would like to know how you OO Guys really work (references to books or
articles would be great).

Don't you design your database the same way that you design you Business
Model if you are responsible for all 3 layers/tiers?

How much time does you spend on writing the DAL (the mapping between the OO
and the Database)? Do you use any kind of O/R Mappers to help you write the
DAL?

Where do you place the tiers in a Smart Client configuration? The way I see
it the UI and Domain Model must be on the client. Because you Domain Model
contains a lot of information e.g. about validation the input, and I don't
want a Server Round Trip every time the users enters something in a textbox.
But I'm also thinking about putting the same domain objects on the server
aswell and use some kind of serialization using .NET Remoting or Web
Services. Anyone else placing the Domain Model on both the Client and
Server?

Can you recommend any third party frameworks, which addresses any of these
problems? I find many of the MS Reference application to be to exotic.

I know these are big questions for a thread in a newsgroup... but never the
less, I haven't found any books or articles that really deals with these
issues.

Best regards,
Thomas
MCSD, MCSE+I, MCP+SB

 

[Jay B. Harlow [MVP - Outlook]]

Thomas,
I would consider a Table Module & Table Data Gateway approach if my "Domain
objects" did not have any real logic to them. See
http://www.martinfowler.com/eaaCatalog/tableModule.html &
http://www.martinfowler.com/eaaCatalog/tableDataGateway.html patterns. I
consider DataSets (both typed & untyped) to be ideal for implementing Table
Module & Table Data Gateways.

However if my "Domain Objects" had heavy logic to them, then I would use a
Domain Model and Data Mapper approach. See:
http://www.martinfowler.com/eaaCatalog/domainModel.html &
http://www.martinfowler.com/eaaCatalog/dataMapper.html patterns.

Don't you design your database the same way that you design you Business
Model if you are responsible for all 3 layers/tiers?

I don't (at least I attempt not to) when using a Domain Model, although they
may be close. Martin's PoEAA has a number of patterns useful here.

However! with Table Module they tend to work out that way.

How much time does you spend on writing the DAL (the mapping between the
OO
and the Database)? Do you use any kind of O/R Mappers to help you write
the
DAL?

I have not used an O/R mapper yet.

Can you recommend any third party frameworks, which addresses any of these
problems? I find many of the MS Reference application to be to exotic.

Rockford Lhotka's book "Expert One-on-One Visual Basic .NET Business
Objects" from A! Press provides a pre-implemented variation of Fowler's
Domain Model & Data Mapper patterns. See CSLA.NET at:
http://www.lhotka.net/

Services. Anyone else placing the Domain Model on both the Client and
Server?

Lhotka's CSLA.NET is leverages .NET remoting if you choose to use it.


Hope this helps
Jay

Hello

I've been reading a lot of great OOD/OOP books lately (e.g.. Martin
Fowlers
UML Distilled, Patterns of Enterprise Application Architecture,
Refactoring,
Kent Becks's Test Driven Development, and also a book called Design
Patterns
Explained.)... al of them with the focus on Java, because I think the best
books are targeted Java. But the all fit very well to the .NET platform.

I have one big problem when reading these great books, and that is that
they
focus almost entirely on the Domain Model (that is the Middle Layer in a 3
layered architecture). They hardly mention that the code you write is to
be
used in a UI interface and committed to a database ([PoEAA] might be an
exception). I find the separation of Business Login and UI to be the
hardest
thing. And also I find the performance issues when talking to the Database
to a very tricky thing, that calls for a few hack in the Domain Layer (I'm
almost only doing thick clients... that is no web).

So I would like to know how you OO Guys really work (references to books
or
articles would be great).

Don't you design your database the same way that you design you Business
Model if you are responsible for all 3 layers/tiers?

How much time does you spend on writing the DAL (the mapping between the
OO
and the Database)? Do you use any kind of O/R Mappers to help you write
the
DAL?

Where do you place the tiers in a Smart Client configuration? The way I
see
it the UI and Domain Model must be on the client. Because you Domain Model
contains a lot of information e.g. about validation the input, and I don't
want a Server Round Trip every time the users enters something in a
textbox.
But I'm also thinking about putting the same domain objects on the server
aswell and use some kind of serialization using .NET Remoting or Web
Services. Anyone else placing the Domain Model on both the Client and
Server?

Can you recommend any third party frameworks, which addresses any of these
problems? I find many of the MS Reference application to be to exotic.

I know these are big questions for a thread in a newsgroup... but never
the
less, I haven't found any books or articles that really deals with these
issues.

Best regards,
Thomas
MCSD, MCSE+I, MCP+SB

 

[Thomas Jespersen]

Hello Nick

Thanks for you input.

First... Yes, you are right, I haven't read the GoF book yet. I thought I
start with something a bit lighter which Design Patterns Explained was (a
great introduction to OOD though). Is it readable for a .NET guy?

Buschmann... never heard of him (embarrassed smiley here). I took a look on
Amazon... can you recommend a specific book?

I read a lot from the Microsoft Patterns & Practices group. I like the
Application Blocks, although I don't really see them as a design guide....
they are just... well Application Blocks.

Regarding my problem about separating the Business and the UI. I agree that
business rules is much more than validation. But I often find that all kind
of rules are need in the UI. E.g. which menu items is shown, warnings and
other things to make sure that exceptions doesn't occurs when calling the
Domain Model. This might sound odd, but e.g. I might have a rule that I
can't call Customer.AddContactInformation, if the customer is inactive or
unsaved. So I'd make a Property on the Customer called
AddContactInformationAllowed. I use this property to decide whether a
certain menu option is available, and/or I call this before
AddContactInformation, to make sure that it doesn't throw an exception.

For me this kind of interaction is a must to make a usable client
application (which is what's count in the end... at least for me), but I
don't se much of this kind in the OO books. But I will consider splitting up
the Domain Model in two (on for validation like things, and one for hiding
business rules)... I'm just not quit sure that this is doable, if related
responsibilities is to be grouped on the same object.

Thomas

Yes... that's a lot for a newsgroup.

Start here:
http://www.microsoft.com/resources/practices/default.mspx

I, too, have read many of the same books. You didn't mention the Design
Patterns book itself (Gang of Four: Gamma, Helm, Johnson, and Vlissides) but
it, too, is an excellent volume. There are also a number of patterns books
that describe code in C# that have been coming out in the past two years.

The books do not focus on a particular tier. The Design Patterns books,
specifically, focus on a specific level of abstraction. The Fowler book
focuses on a different level of abstraction. Buschmann takes on the
architectural level. Honestly, to answer your questions, Buschmann is the
best of the group.

The Microsoft site has some very specific advice for the .NET platform with
regards to optimizations... worth looking into.

As for me: my middle tier is normally tailored to one thing: hiding the
business rules. That requires real analysis: what are the business rules...
what will change... how will they change... how will we maintain them.

Config files are not good for business rule changes... they are too
tactical. You can change the name of a stored proc in the config file. To
change the business rules, you need to encapsulate logic, not just
constants. Using pluggable components will only get you so far.

So, if the business layer has very few business rules, it's really thin.
For many purposes, especially for domain tables (lookup tables), I don't
have any logic at all in the middle tier. In that case, I often simply pass
the data through directly from the DAL to the UI layer as an array of
DataRows. I'll even occasionally bind directly to a control (not often, but
for drop-downs, it's good). On the other hand, if the business layer has
business rules to encapsulate, then I will organize the objects so that
managing those rules makes sense. This is where we start to deviate from
"business objects that mirror the database". This is where the design
patterns come in handy. You really have to map your data into objects that
isolate change and minimize complexity.

I've yet to find a tool or framework that does more than simply
copy-and-reflect operations from the database through the middle tier. I
don't use them. WHat a massive waste of time and processing power. Heck...
the DataSet object does a better job than most of these, and it doesn't
require a huge amount of effort to use! (I don't use it either... I'm just
making a point).

As for copying the validation rules: For a thick client app, I'd have the
same validation dll on both the client and the server. That way, you can
insure common rules. Note: business rules are much more than validation.
I'd have basic validation types that I can use in both places, but the rest
of the rules are quite different.

As for use of remoting: depends on the kind and style of scalability you
want to achieve. For my preference, remoting is too tightly coupled for the
kinds of things that I do... I tend toward web services... but that may not
be advice that you can use... depends on your app.

I hope this info is helpful.
--- Nick Malik
Application Architect
MCSD, CFPS, Certified Scrummaster

Hello

I've been reading a lot of great OOD/OOP books lately (e.g.. Martin Fowlers
UML Distilled, Patterns of Enterprise Application Architecture, Refactoring,
Kent Becks's Test Driven Development, and also a book called Design Patterns
Explained.)... al of them with the focus on Java, because I think the best
books are targeted Java. But the all fit very well to the .NET platform.

I have one big problem when reading these great books, and that is that they
focus almost entirely on the Domain Model (that is the Middle Layer in a 3
layered architecture). They hardly mention that the code you write is to be
used in a UI interface and committed to a database ([PoEAA] might be an
exception). I find the separation of Business Login and UI to be the hardest
thing. And also I find the performance issues when talking to the Database
to a very tricky thing, that calls for a few hack in the Domain Layer (I'm
almost only doing thick clients... that is no web).

So I would like to know how you OO Guys really work (references to books or
articles would be great).

Don't you design your database the same way that you design you Business
Model if you are responsible for all 3 layers/tiers?

How much time does you spend on writing the DAL (the mapping between the OO
and the Database)? Do you use any kind of O/R Mappers to help you write the
DAL?

Where do you place the tiers in a Smart Client configuration? The way I see
it the UI and Domain Model must be on the client. Because you Domain Model
contains a lot of information e.g. about validation the input, and I don't
want a Server Round Trip every time the users enters something in a textbox.
But I'm also thinking about putting the same domain objects on the server
aswell and use some kind of serialization using .NET Remoting or Web
Services. Anyone else placing the Domain Model on both the Client and
Server?

Can you recommend any third party frameworks, which addresses any of these
problems? I find many of the MS Reference application to be to exotic.

I know these are big questions for a thread in a newsgroup... but never the
less, I haven't found any books or articles that really deals with these
issues.

Best regards,
Thomas
MCSD, MCSE+I, MCP+SB

 

[Jay B. Harlow [MVP - Outlook]]

Thomas,
I would recommend Joshua Kerievsky's book "Refactoring to Patterns" by
Addison-Wesley.

In stead of a AddContactInformationAllowed property I would consider
implementing some form of Self-Evaluating Rule. Where the domain object
offers the UI a collection or composite of Self-Evaluating Rules that
indicate to the UI what is or is not allowed. This allows the UI to easily
validate against the domain object without the domain object raising
exceptions. Also its allows the UI to be one step further decoupled from the
domain. If I went the Self-Evaluating Rule approach I would consider making
controls that are Self-Evaluating Rule aware...

Self-Evaluating Rule are defined by David West in his book "Object Thinking"
from MS Press.

Hope this helps
Jay

Hello Nick

Thanks for you input.

First... Yes, you are right, I haven't read the GoF book yet. I thought I
start with something a bit lighter which Design Patterns Explained was (a
great introduction to OOD though). Is it readable for a .NET guy?

Buschmann... never heard of him (embarrassed smiley here). I took a look
on
Amazon... can you recommend a specific book?

I read a lot from the Microsoft Patterns & Practices group. I like the
Application Blocks, although I don't really see them as a design guide....
they are just... well Application Blocks.

Regarding my problem about separating the Business and the UI. I agree
that
business rules is much more than validation. But I often find that all
kind
of rules are need in the UI. E.g. which menu items is shown, warnings and
other things to make sure that exceptions doesn't occurs when calling the
Domain Model. This might sound odd, but e.g. I might have a rule that I
can't call Customer.AddContactInformation, if the customer is inactive or
unsaved. So I'd make a Property on the Customer called
AddContactInformationAllowed. I use this property to decide whether a
certain menu option is available, and/or I call this before
AddContactInformation, to make sure that it doesn't throw an exception.

For me this kind of interaction is a must to make a usable client
application (which is what's count in the end... at least for me), but I
don't se much of this kind in the OO books. But I will consider splitting
up
the Domain Model in two (on for validation like things, and one for hiding
business rules)... I'm just not quit sure that this is doable, if related
responsibilities is to be grouped on the same object.

Thomas

Yes... that's a lot for a newsgroup.

Start here:
http://www.microsoft.com/resources/practices/default.mspx

I, too, have read many of the same books. You didn't mention the Design
Patterns book itself (Gang of Four: Gamma, Helm, Johnson, and Vlissides) but
it, too, is an excellent volume. There are also a number of patterns books
that describe code in C# that have been coming out in the past two years.

The books do not focus on a particular tier. The Design Patterns books,
specifically, focus on a specific level of abstraction. The Fowler book
focuses on a different level of abstraction. Buschmann takes on the
architectural level. Honestly, to answer your questions, Buschmann is
the
best of the group.

The Microsoft site has some very specific advice for the .NET platform with
regards to optimizations... worth looking into.

As for me: my middle tier is normally tailored to one thing: hiding the
business rules. That requires real analysis: what are the business rules...
what will change... how will they change... how will we maintain them.

Config files are not good for business rule changes... they are too
tactical. You can change the name of a stored proc in the config file. To
change the business rules, you need to encapsulate logic, not just
constants. Using pluggable components will only get you so far.

So, if the business layer has very few business rules, it's really thin.
For many purposes, especially for domain tables (lookup tables), I don't
have any logic at all in the middle tier. In that case, I often simply pass
the data through directly from the DAL to the UI layer as an array of
DataRows. I'll even occasionally bind directly to a control (not often, but
for drop-downs, it's good). On the other hand, if the business layer has
business rules to encapsulate, then I will organize the objects so that
managing those rules makes sense. This is where we start to deviate from
"business objects that mirror the database". This is where the design
patterns come in handy. You really have to map your data into objects that
isolate change and minimize complexity.

I've yet to find a tool or framework that does more than simply
copy-and-reflect operations from the database through the middle tier. I
don't use them. WHat a massive waste of time and processing power. Heck...
the DataSet object does a better job than most of these, and it doesn't
require a huge amount of effort to use! (I don't use it either... I'm just
making a point).

As for copying the validation rules: For a thick client app, I'd have the
same validation dll on both the client and the server. That way, you can
insure common rules. Note: business rules are much more than validation.
I'd have basic validation types that I can use in both places, but the rest
of the rules are quite different.

As for use of remoting: depends on the kind and style of scalability you
want to achieve. For my preference, remoting is too tightly coupled for the
kinds of things that I do... I tend toward web services... but that may not
be advice that you can use... depends on your app.

I hope this info is helpful.
--- Nick Malik
Application Architect
MCSD, CFPS, Certified Scrummaster

Hello

I've been reading a lot of great OOD/OOP books lately (e.g.. Martin Fowlers
UML Distilled, Patterns of Enterprise Application Architecture, Refactoring,
Kent Becks's Test Driven Development, and also a book called Design Patterns
Explained.)... al of them with the focus on Java, because I think the best
books are targeted Java. But the all fit very well to the .NET
platform.

I have one big problem when reading these great books, and that is that they
focus almost entirely on the Domain Model (that is the Middle Layer in
a 3
layered architecture). They hardly mention that the code you write is
to be
used in a UI interface and committed to a database ([PoEAA] might be an
exception). I find the separation of Business Login and UI to be the hardest
thing. And also I find the performance issues when talking to the Database
to a very tricky thing, that calls for a few hack in the Domain Layer (I'm
almost only doing thick clients... that is no web).

So I would like to know how you OO Guys really work (references to
books or
articles would be great).

Don't you design your database the same way that you design you
Business
Model if you are responsible for all 3 layers/tiers?

How much time does you spend on writing the DAL (the mapping between
the OO
and the Database)? Do you use any kind of O/R Mappers to help you write the
DAL?

Where do you place the tiers in a Smart Client configuration? The way I see
it the UI and Domain Model must be on the client. Because you Domain Model
contains a lot of information e.g. about validation the input, and I don't
want a Server Round Trip every time the users enters something in a textbox.
But I'm also thinking about putting the same domain objects on the server
aswell and use some kind of serialization using .NET Remoting or Web
Services. Anyone else placing the Domain Model on both the Client and
Server?

Can you recommend any third party frameworks, which addresses any of these
problems? I find many of the MS Reference application to be to exotic.

I know these are big questions for a thread in a newsgroup... but never the
less, I haven't found any books or articles that really deals with
these
issues.

Best regards,
Thomas
MCSD, MCSE+I, MCP+SB

 

[Nick Malik]

Buschmann: Pattern Oriented Software Architecture
http://www.amazon.com/exec/obidos/t...f=sr_1_1/104-0692560-9975161?v=glance&s=books

Microsoft Patterns and Practices: discussion of the Layers pattern (Not an
application block!)
http://msdn.microsoft.com/library/d...-us/dnpatterns/html/ArcLayeredApplication.asp

GoF is never easy. But it is much more comprehensive than the DP Explained
book.

Now: for the follow-up:
If you view the interaction with the domain model as a series of messages,
then it's not too difficult to seperate the View from the Model.

In other words, you wouldn't need to warn the user that they cannot add
contact information on the unsaved user record, since the act of adding
contact information would necessarily trigger a request to send the user
record to the domain model. Either that, or you don't prevent the user from
adding contact info to an unsaved record. (Why NOT add contact info to an
unsaved user? The most common reason I hear is when folks are using
Identity columns as their primary keys in the Database... but that's easy to
work around... use GUIDs. Since the app can generate a unique id, there is
no need to create a transaction to write a record just to get the joining
data value back. Just create the Guid, use it as the primary key in one
message, and the foreign key in another. No problems and no need to
round-trip one transaction before generating another).

That goes back to my comment about creating a services interface between the
front end and the domain model. It really forces you to decouple your
system.

Good luck and I hope this helps,

--- Nick

Hello Nick

Thanks for you input.

First... Yes, you are right, I haven't read the GoF book yet. I thought I
start with something a bit lighter which Design Patterns Explained was (a
great introduction to OOD though). Is it readable for a .NET guy?

Buschmann... never heard of him (embarrassed smiley here). I took a look on
Amazon... can you recommend a specific book?

I read a lot from the Microsoft Patterns & Practices group. I like the
Application Blocks, although I don't really see them as a design guide....
they are just... well Application Blocks.

Regarding my problem about separating the Business and the UI. I agree that
business rules is much more than validation. But I often find that all kind
of rules are need in the UI. E.g. which menu items is shown, warnings and
other things to make sure that exceptions doesn't occurs when calling the
Domain Model. This might sound odd, but e.g. I might have a rule that I
can't call Customer.AddContactInformation, if the customer is inactive or
unsaved. So I'd make a Property on the Customer called
AddContactInformationAllowed. I use this property to decide whether a
certain menu option is available, and/or I call this before
AddContactInformation, to make sure that it doesn't throw an exception.

For me this kind of interaction is a must to make a usable client
application (which is what's count in the end... at least for me), but I
don't se much of this kind in the OO books. But I will consider splitting up
the Domain Model in two (on for validation like things, and one for hiding
business rules)... I'm just not quit sure that this is doable, if related
responsibilities is to be grouped on the same object.

Thomas

Yes... that's a lot for a newsgroup.

Start here:
http://www.microsoft.com/resources/practices/default.mspx

I, too, have read many of the same books. You didn't mention the Design
Patterns book itself (Gang of Four: Gamma, Helm, Johnson, and Vlissides) but
it, too, is an excellent volume. There are also a number of patterns books
that describe code in C# that have been coming out in the past two years.

The books do not focus on a particular tier. The Design Patterns books,
specifically, focus on a specific level of abstraction. The Fowler book
focuses on a different level of abstraction. Buschmann takes on the
architectural level. Honestly, to answer your questions, Buschmann is the
best of the group.

The Microsoft site has some very specific advice for the .NET platform with
regards to optimizations... worth looking into.

As for me: my middle tier is normally tailored to one thing: hiding the
business rules. That requires real analysis: what are the business rules...
what will change... how will they change... how will we maintain them.

Config files are not good for business rule changes... they are too
tactical. You can change the name of a stored proc in the config file. To
change the business rules, you need to encapsulate logic, not just
constants. Using pluggable components will only get you so far.

So, if the business layer has very few business rules, it's really thin.
For many purposes, especially for domain tables (lookup tables), I don't
have any logic at all in the middle tier. In that case, I often simply pass
the data through directly from the DAL to the UI layer as an array of
DataRows. I'll even occasionally bind directly to a control (not often, but
for drop-downs, it's good). On the other hand, if the business layer has
business rules to encapsulate, then I will organize the objects so that
managing those rules makes sense. This is where we start to deviate from
"business objects that mirror the database". This is where the design
patterns come in handy. You really have to map your data into objects that
isolate change and minimize complexity.

I've yet to find a tool or framework that does more than simply
copy-and-reflect operations from the database through the middle tier. I
don't use them. WHat a massive waste of time and processing power. Heck...
the DataSet object does a better job than most of these, and it doesn't
require a huge amount of effort to use! (I don't use it either... I'm just
making a point).

As for copying the validation rules: For a thick client app, I'd have the
same validation dll on both the client and the server. That way, you can
insure common rules. Note: business rules are much more than validation.
I'd have basic validation types that I can use in both places, but the rest
of the rules are quite different.

As for use of remoting: depends on the kind and style of scalability you
want to achieve. For my preference, remoting is too tightly coupled for the
kinds of things that I do... I tend toward web services... but that may not
be advice that you can use... depends on your app.

I hope this info is helpful.
--- Nick Malik
Application Architect
MCSD, CFPS, Certified Scrummaster
that
they

a

3

layered architecture). They hardly mention that the code you write is

to
be

used in a UI interface and committed to a database ([PoEAA] might be an
exception). I find the separation of Business Login and UI to be the hardest
thing. And also I find the performance issues when talking to the Database
to a very tricky thing, that calls for a few hack in the Domain Layer (I'm
almost only doing thick clients... that is no web).

So I would like to know how you OO Guys really work (references to

books
or

articles would be great).

Don't you design your database the same way that you design you Business
Model if you are responsible for all 3 layers/tiers?

How much time does you spend on writing the DAL (the mapping between

the
OO

and the Database)? Do you use any kind of O/R Mappers to help you

write
the

DAL?

Where do you place the tiers in a Smart Client configuration? The way

I
see

it the UI and Domain Model must be on the client. Because you Domain Model
contains a lot of information e.g. about validation the input, and I don't
want a Server Round Trip every time the users enters something in a textbox.
But I'm also thinking about putting the same domain objects on the server
aswell and use some kind of serialization using .NET Remoting or Web
Services. Anyone else placing the Domain Model on both the Client and
Server?

Can you recommend any third party frameworks, which addresses any of these
problems? I find many of the MS Reference application to be to exotic.

I know these are big questions for a thread in a newsgroup... but

never
the

less, I haven't found any books or articles that really deals with these
issues.

Best regards,
Thomas
MCSD, MCSE+I, MCP+SB