fig many to many relationship is depicted in fig the forks on the two ends of the line represent the manyto-many relationship between feeds and feed attribute types many-to-many relationships cannot be represented in relational database without going through process called reification reification introduces new entities that remove many-to-many relationships when many-to-many relationship appears within logical data structure it indicates there may be missing attributes in this casethe quantity of each nutrient within feed was missing the new feedattribute entity eliminates the many-to-many relationship by introducing two one-to-many relationships one-to-many relationships can be represented in relational databases every entity in relational database must have unique identifier in fig the feed entities are uniquely identified by their feedid attribute the other attributes are importantbut do not have to be unique each feedid must be unique and it cannot be null or empty for any feed likewisea feedattribtypeid field uniquely identifies each feed nutrient there is unique feedattribtypeid for calciumironand so on the feedattribute entity has unique id made up of two fields togetherthe feedid and the feedattribtypeid identify unique instance of nutrient for particular feed the value was the missing attribute in fig that was introduced by reifying the many-to-many relationship as depicted in fig the logical data structure in fig describes the schema for feeds and nutrients in the dairy database relational database is composed of tables and the shema provides the definition of these tables the feed table consists of rows and columns each row in the feed table describes one feed the columns of the feed table are each of the attributes of feed provided in fig the example in sect provides subset of this table fig logical data structure this copy belongs to 'acha