Unit 12: Introduction to Multitier Application Development

1
Unit 12 Introduction to Multi-tier Application
Development

• Review Model-View Separation
• Client-Server Architecture
• BCB Multi-tier Distributed Application Services
  (MIDAS)
• BCB Remote Data Module
• TDataSetProvider
• TClientDataSet

2
BCB Model-View Separation

• Business Logic
• Data Module (i.e., Model)
• Presentation logic
• Form (i.e., View)
• Using Data Module
• Pro Code is maintainable
• Con Fat client
• business logic distributed to all clients
• If business logic changes, need to re-deploy to
  all clients

3
Client-Server Architecture

• Fat Client Form and Data Module
• Server Centralized Database

Fat Client
DataModule.cpp
SQL Server
TADO Connection
TDataSource
TADOTable
4
Multi-tier Architecture

• BCB Multi-tier Distributed Application Services
  (MIDAS)
• Application resides in three (or more) machines
• Thin Client Form and Client Data Module
• Middle-tier Remote Data Module
• Business logic stored in the Remote Data Module
• BCB DataSetProvider encapsulates the COM
  interface and exports the DataSet to clients
• Also known as Application Server
• Server Centralized Database
• SQL Server, Oracle, Sybase, DB2, MySQL

5
MIDAS Remote Data Module
Thin Client
DataModule.cpp
TClient DataSet
DCOM Connection
TDataSource
TDataSet Provider
RemoteDataModule.cpp
TADO Connection
SQL Server
TADOTable
Middle-tier
6
Remote Data Module

• RDM uses COM IAppServer interface
• Client needs MIDAS.dll to connect to the
  TDataSetProvider
• TDataSetProvider
• Exports the DataSet and makes it available for
  clients.
• Must set Export property to true

7
DCOM Connection

• Pros
• BCB supports DCOM using TDCOMConnection component
• Simplifies connection from client to middle-tier
• Cons
• DCOM is a Microsoft platform only solution
• Requires NT/W2K
• Requires MS Domain Name Server (DNS)
• Requires admin rights to DCOM config and security

8
TClientDataSet

• Similar to the regular TDataSet such as TADOTable
  and TADOQuery
• Key Properties
• Remote Server
• Use the DCOMConnection in DM
• Provider Name
• Use the DataSetProvider name in Remote DM
• Key Method
• ApplyUpdates(0) to propagate changes to RDM
• Argument of zero (0) means to stop updates if an
  error or exception is encountered.

9
RDM Exercise
Extra Use COM interface for additional business
logic
10
Assignment 6

• Objective Convert a Data Module to Remote Data
  Module
• Now available due next week
• Testing limited to one machine only
• Avoid DCOM setup issues security/ access,
  packaging and interface (MIDAS.dll), DNS and RPC
  server availability, etc.
• Use MS Access (PayData2002.mdb)
• Use Remote Data Module for middle-tier
• Use DCOM Connection for thin-client