Expanding on Michael and Darshil's good answers, it's not that the Marketo database is "not relational." It's entirely relational. But, like in any app, that doesn't mean you should expect an individual CRUD interface for every table/view. Marketo only considers Leads to be "first-class" records. Many native concepts, such as forms and even web activities, are not even first-class in the sense that you can't pivot a report around them.
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