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Thread: I am confused....

  1. #1
    Antonio Paglia Guest

    I am confused....

    I am developing a win32 three-tier application using VB6, MTS and Oracle
    Server.
    The layers are :

    - Presentation layer:
    EXE ActiveX projects:. Forms, Reports and modules used by users to
    interact with the entire application.
    -Object Model
    DLL ActiveX projects. Business Rules are in this layer. Objects are
    statefull.
    -Data Service
    DLL ActiveX projects. This objects are stateless and runs inside MTS

    Imaginate that the user wants (through the form) to save the changes done
    to an invoice. The Business layer before to save the Invoice object,
    validate the data entered by the user. These objects are statefull. For this
    reason, the user can get and set all properties and execute any methods of
    these objects.
    If all are correct, the data are sent to the Data Service layer - object
    stateless (MTS) who will be the one in charge to access to the database.

    This is my question.

    Jim Maloney in his book (Distributed COM. Application Development using VB
    6.0) , when he talk about Browser-Based application says:

    "A browser-based presentation layer client use ASP or IIS application, which
    bypass the object model and directly use the stateless object in the Data
    Service Layer" ....

    First Question
    Where are the Business rules in this case ? Presentation o Data Service
    Layer ?

    Second Question
    Are Internet Application n-tier or two-tier architecture ?

    Third Question
    Assuming that in a future I wish that my whole application can also be used
    in Internet, can the businesses rules and the Data Service layer being
    reused?

    Any opinion will be appreciated
    Antonio






  2. #2
    ranga raghunathan Guest

    Re: I am confused....


    "Antonio Paglia" <apaglia@infovia.com.ar> wrote:
    >>"A browser-based presentation layer client use ASP or IIS application,

    which >bypass the object model and directly use the stateless object in the
    Data >Service Layer" ....
    >>First Question

    >Where are the Business rules in this case ? Presentation o Data Service

    Layer ?
    Answer : First, to recollect, in Web apps, Presentation layer (html,asp etc)
    resides on the web server and are "brought" to the client after the client
    requests the page .. this does not mean that all business rules are executed
    on the web server .. after the asp page is brought to the client, certain
    business rules can be executed in the client side itself using javascript
    or vbscript .. for example, data entry business rules can be done on the
    client machine.

    >Second Question
    >Are Internet Application n-tier or two-tier architecture ?

    Reply: = while internet applications are generally thought of to be n-tier
    apps, note that tiers are logical -- you can have n tiers logically but deploy
    them in different ways physically -- say you have gui-exe, busienss-dll and
    oracle database - this is logical 3-tier but you can deploy them in several
    phyiscal tiers as follows
    physical 3 -tier -- gui-exe on client machine (say win 95)
    -- business dll on app server (nt server)
    -- database on db server (nt server)
    physical 2 tier -- gui-exe and business-dll on client machine
    -- database in db server (nt server)
    the physical 2-tier is not recommended since you cannot take advantage
    of mts

    in the internet case, several scenarios are possible
    - web server (html,asp),appserver(dll), and db server all on 1 machine --
    not recommended for high volume sites - but still possible to do this --
    logical 3-tier but physically 1 machine takes care of all
    --web server (html,asp),appserver(dll) on 1 machine and db server on 1 machine
    - logical 3-tier but physical 2 tier
    -- web server (html,asp),appserver(dll), and db server all on
    3 different machines -- logical 3-tier and physical 3-tier

    -- in light-weight internet/intranets, you can even put your business logic
    in asp itslef and eliminate the business-dll. In this case you have web server
    (html-gui,asp-business logic) and database -- again this can be deployed
    in a physical 1-tier or a physical 2-tier depending on the location of the
    database

    As you can see, you can mix and match -- the key is to keep your gui and
    business logic separate ..
    >Third Question
    >Assuming that in a future I wish that my whole application can also be

    used >in Internet, can the businesses rules and the Data Service layer being
    reused?
    Reply -- Yes - you can for example change your rich-client exe with a thin-client
    such as asp..

    -- > note that some books refer to the data objects (dlls) as the third tier
    -- this is kind of confusing -- the 3-rd tier is most often the database
    itself with stored proc etc .. the 2nd tier (middle tier) may have business
    dlls and data-access dlls --the business dlls may be stateful and run outside
    of mts and the data-access dlls can run inside mts ..

    >
    >Any opinion will be appreciated

    Reply -- the reply to your email is based on my experience .. others may
    agree or disagree ..will have to wait and see..

    >Antonio
    >

    regards
    ranga

  3. #3
    Kurt Guest

    Re: I am confused....


    Read Professional Visual Basic 5 or 6 Bussiness Objects. there is a great
    working sample with VB as front end as well as ASP pages. With the UI object
    (Business layer) still is used.

    Though this is all new to me, we are currently designing a 3 tier application
    with VB front end as well as ASP. Another note is to do your scripting code
    in a VB project, and only create the object in the ASP page Refer to ACCESS
    VB*SQL Advisor May 2000 issue. The name of the article is "Use VB to Create
    ASP pages. by Micheal D. Krasowski. Then you can use your business logic,
    troubleshoot your code...., and no late binding.. faster.. faster.

    "Antonio Paglia" <apaglia@infovia.com.ar> wrote:
    >I am developing a win32 three-tier application using VB6, MTS and Oracle
    >Server.
    >The layers are :
    >
    >- Presentation layer:
    > EXE ActiveX projects:. Forms, Reports and modules used by users to
    >interact with the entire application.
    >-Object Model
    > DLL ActiveX projects. Business Rules are in this layer. Objects are
    >statefull.
    >-Data Service
    > DLL ActiveX projects. This objects are stateless and runs inside MTS
    >
    >Imaginate that the user wants (through the form) to save the changes done
    >to an invoice. The Business layer before to save the Invoice object,
    >validate the data entered by the user. These objects are statefull. For

    this
    >reason, the user can get and set all properties and execute any methods

    of
    >these objects.
    >If all are correct, the data are sent to the Data Service layer - object
    >stateless (MTS) who will be the one in charge to access to the database.
    >
    >This is my question.
    >
    >Jim Maloney in his book (Distributed COM. Application Development using

    VB
    >6.0) , when he talk about Browser-Based application says:
    >
    >"A browser-based presentation layer client use ASP or IIS application, which
    >bypass the object model and directly use the stateless object in the Data
    >Service Layer" ....
    >
    >First Question
    >Where are the Business rules in this case ? Presentation o Data Service
    >Layer ?
    >
    >Second Question
    >Are Internet Application n-tier or two-tier architecture ?
    >
    >Third Question
    >Assuming that in a future I wish that my whole application can also be

    used
    >in Internet, can the businesses rules and the Data Service layer being
    >reused?
    >
    >Any opinion will be appreciated
    >Antonio
    >
    >
    >
    >
    >



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