A coalgebraic equational approach to specifying observational structures

A coalgebraic, equational approach to the speci(cation of observational structures allowing for a choice in the result type of observations is presented. Observers whose result type is structured as a coproduct of basic types are considered, and notions of covariable, coterm and coequation, dual to the algebraic notions of variable, term and equation are used to specify the associated structures. A sound and complete deduction calculus for reasoning about observational structures is then formulated. Finally, the approach is extended in order to account for the availability of a (xed data universe in the speci(cation of such structures. c © 2002 Elsevier Science B.V. All rights reserved.