Data modelling reveals the internal structure of an information system, abstracting away
from details of the physical representation. We show that entity-relationship modelling, a
well-tried example of a data-modelling technique, can be applied to both interactive and
non-interactive information artefacts in the domain of HCI. By extending the conventional
ER notation slightly (to give ERMIA, Entity-Relationship Modelling for Information
Artefacts) it can be used to describe differences between different representations of the same
information, differences between user’s conceptual models of the same device, and the
structure and update requirements of distributed information in a worksystem. It also yields
symbolic-level estimates of Card et al.’s (1994) index of ‘cost-of-knowledge’ in an information
structure, plus a novel index, the ‘cost-of-update’; these symbolic estimates offer a useful
complement to the highly detailed analyses of time costs obtainable from GOMS-like
models. We conclude that, as a cheap, coarse-grained, and easy-to-learn modelling
technique, ERMIA usefully fills a gap in the range of available HCI analysis techniques