2.4 Class Signatures

Signature-F-atoms define the attributes applicable for instances of certain classes. These definitions are similar to method declaration in object-oriented languages. A signature-F-atom declares an attribute on a class and gives type restrictions for   results.   To distinguish signature-F-atoms from data- F-atoms, the arrow body consists of a double line instead of a single line. Here are some examples for signature-F-atoms along with their graphic representation.

person[father=>man].              We will represent signatures by ellipses filled with color:  

dot-code                  

This  states that the single-valued attribute father is defined for members of the class person and the content of this attribute  has to belong to the class man.

The signatures for multi-valued attributes are represented by double headed arrows:  person[daughter=>>woman] .    Here is the graphic form of the same statement:

  dot-code       

 By using a list of result classes enclosed by parentheses, several signature-F-atoms may be combined in an F-molecule. This is equivalent to the conjunction of the atoms: the content of the attribute is required to be in all of those classes:

person[father=>(man, person)].

 dot-code

Here are  the definitions for stock and flow pertained to the   description of biogeochemical cycles. Similar definitions will be used in real biogeochemical cycles model in ESD (see next section)

stock[agent=>chemical_agent, ispartof=>container, quantity=>value].
flow[source=>stock, target=>stock, agent=>chemical_agent, intensity=>value].

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