Is it possible to achive 100% descriptive programming in TestComplte.?? For the desktop application

Define "descriptive programming".

If you mean the concept used in HP QTP/UFT, that is, identifying objects without using the Object Repository - yes TestComplete supports this too. You do this by using the object names seen in the Object Browser and/or the Find* methods.

For example:

Sys.Process("explorer").Window("Button", "Start").Click();

is a "descriptive programming" version of

Aliases.explorer.btnStart.Click();

Check out these threads for more examples:
Can we do descriptive programming
descriptive programming with Python