All columns (variables): patent_number, grantdate, prioritydate, prioritycountry, prioritypatentnumber, cpcsubgroup, pctpatentnumber, claims, appnum, grantyear, appdate, appyear, nber, uspc, uspc_sub
===Assignee===
Purpose: Represent the person the patent is currently assigned to according to the patent information (the information in the Assignment database is more complete)
Each entry represents: the assignee for a patent in PATENT
Primary key: patent_number, first_name, last_name (in case it is possible for there to be multiple assignees for an individual patent)
All columns (variables): First name, last name, address, postcode, orgname, city, country, patentnumber, state, residence, size of firm
===Citation===
Purpose: Represent all the patents in PATENT that another patent in PATENT cites
Each entry represents: one citation that a patent in PATENT makes
Primary key: patent_number AND cited_patent_number (because a patent might cite multiple patents, so both variables are needed for the primary key)
All columns (variables): patent_number, cited_patent_number
===Fee===
Purpose: Represent information about the fees paid for an individual patent
Each entry represents: information about the fees paid on the patent
Primary key: patent_number
All columns: patent_number, four, eight, twelve, fee_date, fee_code
===HISTPATENT===
Purpose: Represent historical data about the patent pertaining to dates and publication
Each entry represents: sequence of historical data about an individual patent in PATENT
==Connecting Patent database and Assignment database==