Database Modeling edit
- These two pages have a lot of the same content...
Entity-relationship model edit
- Page doesn't define the acronym UML
- What problem with UML is that reference talking about?
- I don't understand the last paragraph here.
- It almost sounds like it's calling UML a platform specific model.
From the page edit
In Dullea et al. one reads "A 'look across' notation such as used in the UML does not effectively represent the semantics of participation constraints imposed on relationships where the degree is higher than binary."
In Feinerer it says "Problems arise if we operate under the look-across semantics as used for UML associations. Hartmann //REF = Hartmann, Sven. "Reasoning about participation constraints and Chen's constraints". Proceedings of the 14th Australasian database conference-Volume 17. Australian Computer Society, Inc., 2003. [1] investigates this situation and shows how and why different transformations fail." (Although the "reduction" mentioned is spurious as the two diagrams 3.4 and 3.5 are in fact the same) and also "As we will see on the next few pages, the look-across interpretation introduces several difficulties which prevent the extension of simple mechanisms from binary to n-ary associations."
...
An extensional model is that which maps to the elements of a particular methodology or technology, and is thus a "platform specific model". The UML specification explicitly states that associations in class models are extensional and this is in fact self-evident by considering the extensive array of additional "adornments" provided by the specification over and above those provided by any of the prior candidate "semantic modelling languages"."UML as a Data Modeling Notation, Part 2"