Microsoft CRM was designed to be easily customizable. Microsoft CRM Software Development Kit (MS CRM SDK) which you can download from Microsoft website contains descriptions of the objects or classes, exposed for customization. It has sample code in C# and partially in VB.Net. In Visual Studio.Net you can analyze all the classes, used by Microsoft developers to create MS CRM - you will discover that most of them are not documented in MS CRM SDK. Microsoft will not support your customization if you use undocumented class or do direct SQL access to CRM database.
Let us describe you - programmer, software developer typical cases of MS CRM Customizations.
1. Integration with SQL Server application. If you have legacy system on MS SQL Server - let's say you are transportation company and have in-house developed cargo tracking database. Now in MS CRM you want lookup the shipments for the customer (or account in CRM). This is SDK programming and calling SQL stored proc to retrieve cargo info. Instead of SQL Server you can have other database (ORACLE, MS Access, PervasiveSQL to name a few) - you can access multiple Database platforms via ADO.Net connection from your .Net application, which is easily integrated into MS CRM Account screen.
2. Email capturing in MS CRM. You have customer with email Bill@customer.com. Now you want all the emails that you receive from customer.com domain to be attached to Bill who is account in CRM. This is more difficult customization - you have to create MS CRM SDK web service, that one will be creating email activity and call it from COM+ application - Microsoft Exchange event handler (ONSYNCSAVE database event sink). This example maybe complicated with the following requirement. Imagine that Bill, instead of answering to your email (sent from CRM and processed by CRM-Exchange connector) sends you new message from MS Outlook. Then this email will not follow into MS CRM (because it doesn't have GUID in the header and so is ignored by CRM Exchange connector). If you want to capture these emails - you have to do it in Microsoft Exchange event sink. There maybe scenario when you want to capture and analyze in the sink all the outgoing emails - this is even more complex - you have to place the sink on transport event.
3. ASP Application integration. You have legacy ASP application, where you capture orders from your customers and you want these orders be transferred to the CRM as activity. Here you understand that ASP doesn't deploy Active Directory security - and the best way is to create HTTP handler and call it from your ASP page. This HTTP handler in turn will call MS CRM SDK web service with predefined (web.config) Active Directory credentials.
Some cautions. Never create your custom SQL objects (like stored procedure, SQL view, table) in MS CRM database. Instead, create your own database and place your objects there. When you see the first caution - you will never try to alter existing CRM objects, like adding new field to the table.
