## Modelling sketches and ERA models

### Bob Rosebrugh – 23 May 2001

Entity-Relationship-Attribute models use a graphical technique for displaying the objects of an information system and relationships among them. A suitable environment for specifying the objects and constraints of a system is the finite-limit, finite-sum sketches with a terminal node (we call them EA sketches). The category of models of an EA sketch in a lextensive category gives states of the system. It is an object of models of the sketch in a 2-category of lextensive categories. Moreover, modelling the same sketch in certain objects in other 2-categories defines both the query language for the system and the updates (the dynamics) for the system. This talk will consider modelling a sketch in an object of a 2-category, and describe the cases just noted.
This is joint work with Michael Johnson and RJ Wood.

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