Tools such as discussion forums, wikis and blogs can enable learners to actively construct knowledge. Examples include social-networking sites, video-sharing sites, wikis, blogs, mashups and folksonomies. Zines, talk radio shows, and group projects also preceded blogs, podcasts, wikis, and social networks. Some wiki farms can also make private, password-protected wikis. The final strategy is user-generated content platforms like blogs or wikis. These include features like forums, blogs, wikis, web stores, photo galleries, and contact management. Other public wikis that run on MediaWiki include wikiHow and SNPedia. Data is also crowdsourced using public wikis and public upload facilities. RationalWiki differs in several ways from the philosophy of Wikipedia and some other informational wikis. Unlike some other online wikis, PetroWiki content is copyrighted by SPE. It features per project wikis and forums, time tracking, and flexible, role-based access control. Similar attacks are often performed against wikis and guestbooks, both of which accept user contributions. These wikis are also available in several languages. There may be greater use of wikis behind firewalls than on the public Internet. Indexed database access is necessary for high speed searches on large wikis.