What little is known is rarely documented by the database producer. Rather, it must be deduced by users. In part, this is due to the simplicity of the records in some databases. They include a title, a link to the URL, and sometimes a description. Yet more detailed explanation of the record structure could be quite useful to searchers.
Some records have the cool sunglasses icon while others actually have a review.
After reading this minimal documentation, users can discover what determines the title, URL, description, and even the subject category. But the other variables related to the structure of records and of the database itself are not clearly identified. Evaluating the structure of a metasite involves both record structure and subject hierarchy structure. One technique is to compare the subject structure to traditional thesauri. A better measure is to compare the metasite's structure with your own understanding of the field.