An algebra and a message oriented language for a data model based on complex objects / Gerard Johan Peter Marie HoubenThe design of an online help facility for exspect / by G-J. HoubenTutorial voor de ExSpect-bibliotheek voor "administratieve logistiek" / door Geert-Jan HoubenA software architecture for generating hypermedia applications for ad-hoc database output / by Geert-Jan Houben and Pim Lemmens