Computer implemented systems store descriptions of multiple different types of marketplace items as a collection of parameter-value pairs, using a table having a plurality of rows and columns, wherein values for at least two of the items are stored in cells of first and second ones of the rows, respectively; keys that provide information that can be used to decipher differential mappings of a plurality of the columns to a plurality of parameters in different ones of the rows; and one or more interfaces that collectively display previously stored parameters and values to a human end-user.