1. A method comprising: accessing data associated with an item offered for sale in an online marketplace; identifying a plurality of attributes associated with the item; generating, using one or more processors, a class, in a JAVA programming language, associated with the item; annotating the class using annotation-type declarations in the JAVA programming language, each of the annotation-type declarations comprising an at sign (@) followed by an interface keyword, the annotation-type declarations comprising first annotation-type declarations that include one or more attributes of the plurality of attributes associated with the item, and the first annotation-type declarations describing the item within source code of the class; and defining, using the one or more processors, one or more rules associated with each of the one or more attributes of the plurality of attributes associated with the item, wherein: the annotation-type declarations describing the item comprise at least one of an item class, an item title, an item price, an item author, an item manufacturer, an item description, or item shipping data; the annotation-type declarations further comprise second annotation-type declarations; and the second annotation-type declarations comprise the one or more rules that are compilable to implement the one or more rules in machine-executable instructions in a runtime environment.