In the first sentence, the article is actually used to refer to the word 'architecture', with ADO.NET simply as an adjective. On the second example, ADO.NET is acting as a noun, and since it is a pronoun, it doesn't need an article (similarly, we say Windows XP, not the Windows XP.)
Similarly for your second example, 'the' is used to refer to 'data type', with timestamp acting as an adjective. Example three also has 'the' referring to 'data type'.
'The' is the article for 'method' in Example 4.
I hope I am clarifying things, instead of making them more messed up.
WJTW