Usually the building block view shall contain only those elements that are specifically created for the system.
In certain cases it can though be helpful (i.e. for better understandability) to include third-party software (i.e. middleware, databases, libraries, frameworks, utilities) in the building block view.
The following diagram shows a whitebox from a HTML semantic analyser software, where the (open-source, third-party) HTML parser is absolutely essential for the system. Therefore its included in the building block view (lower left corner)
(In accordance with tip 5-20 (indicate third-party elements)
it has been marked with the stereotype
library to better distinguish
it from the building blocks specific for the system itself.)