COM+

1. Scalability

• Any system must recycle resources quickly and efficiently
• JIT/ASAP life cycle ensures all resources are recycled to central resource pools at the end of a transaction
• COM+ Load Balancing service direct new clients to lightly loaded servers
• Short component life spans are of great benefit

2. State Management

• "The process which maintains state and page information over multiple requests. As is true for any HTTP-based technology, Web Forms pages are stateless, which means that they do not automatically indicate whether the requests in a sequence are all from the same client or even whether a single browser instance is still actively viewing a page or site. Furthermore, pages are destroyed and recreated with each round trip to the server; therefore page information will not exist beyond the life cycle of a single page"  -- page state management from MSDN
• Provides data integrity by ensuring another transaction cannot access data pertaining to one transaction until the first transaction has completed
• Restrict to access application's data will limit scalability
• All access to data must be performed explicitly by component using a data access mechanism such as ADO (ActiveX Data Objects) or OLE DB (Object Linking and Embedding DataBase)

// OleDbSample.cs
using System;
using System.Data;
using System.Data.OleDb;
using System.Xml.Serialization;

public class MainClass {
    public static void Main ()
    {
            // Set Access connection and select strings.
            string strAccessConn = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=..\\..\\BugTypes.MDB";
            string strAccessSelect = "SELECT * FROM Categories";
 
            // Create the dataset and add the Categories table to it:
            DataSet myDataSet = new DataSet();
            OleDbConnection myAccessConn = null;
            myAccessConn = new OleDbConnection(strAccessConn);
            
            OleDbCommand myAccessCommand = new OleDbCommand(strAccessSelect,myAccessConn);
            OleDbDataAdapter myDataAdapter = new OleDbDataAdapter(myAccessCommand);
 
            myAccessConn.Open();
            myDataAdapter.Fill(myDataSet,"Categories");
 
            myAccessConn.Close();
.......   

3. Simpler Security

• Built on top of Windows 2000 security infrastructure and original COM security mechanism
• A hierarchy of authentication levels
• Access control is defined on per-interface or per-method
• Role-based security to allow access right to be assigned to named roles, such as "administrator"
• Some identity issues still remain, such as identity used to access pooled resources

4. Fault Tolerance

• COM+ Component Load Balancing compensates for a server failure by sending new clients to alternative servers
• Queued components can be delivered when the server is back up -- for existing clients of  the failed server 

5. Ease of Development

• Components calls the SetComplete and SetAbort methods to indicate a transaction outcome
• Call are available in COM-aware languages, such as VB, VC++, and VBScript
• Existing COM components can be used as COM+ components without recoding

6. Help With Deployment

• COM+ applications can be used from any COM-enabled platform
• COM+ server can only run on Windows 2000
• A COM+ application can be exported as a Windows installer package

"In Visual Basic 6.0, you typically used the Package and Deployment Wizard to create a script-based Setup.exe for your application. The Package and Deployment Wizard could be run as a stand-alone tool or as an add-in to Visual Basic; it could only be used with Visual Basic projects.

In Visual Basic .NET, you use a deployment project to create an installer (.msi file) for your application. Unlike the script-based setups, the installer uses Microsoft Windows Installer technology to manage the installation for you. For example, the installer automatically rolls back installation when something goes wrong. " -- from MSDN