Martin notation) (min, max)-notation of Jean-Raymond Abrial in 1974 UML class diagrams Merise Object-role modeling Crow's foot notation Crow's foot notation, the beginning of which dates back to an article by Gordon Everest (1976), is used in Barker's notation, Structured Systems Analysis and Design Method (SSADM) and information technology engineering. Crow's foot diagrams represent entities as boxes, and relationships as lines between the boxes. Different shapes at the ends of these lines represent the relative cardinality of the relationship. Crow's foot notation was used in the consultancy practice CACI. Many of the consultants at CACI (including Richard Barker) subsequently moved to Oracle UK, where they developed the early versions of Oracle's CASE tools, introducing the notation to a wider audience. With this notation, relationships cannot have attributes. Where necessary, relationships are promoted to entities in their own right: for example, if it is necessary to capture where and when an artist performed a song, a new entity "performance" is introduced (with attributes reflecting the time and place), and the relationship of an artist to a song becomes an indirect relationship via the performance (artist-performs-performance, performance-features-song). Three symbols are used to represent cardinality: the ring represents "zero" the dash represents "one" the crow's foot represents "many" or "infinite" These symbols are used in pairs to represent the four types of cardinality that an entity may have in a relationship. The inner component of the notation represents the minimum, and the outer component represents the maximum. ring and dash → minimum zero, maximum one (optional) dash and dash → minimum one, maximum one (mandatory) ring and crow's foot → minimum zero, maximum many (optional) dash and crow's foot → minimum one, maximum many (mandatory) Model usability issues In using a modeled database, users can encounter two well known issues where the returned results mean something other than the results assumed by the query author. The first is the 'fan trap'. It occurs with a (master) table that links to multiple tables in a one-to-many relationship. The issue derives its name from the way the model looks when it's drawn in an entity–relationship diagram: the linked tables 'fan out' from the master table. This type of model looks similar to a star schema, a type of model used in data warehouses. When trying to calculate sums over aggregates using standard SQL over the master table, unexpected (and incorrect) results may occur. The solution