Thos Green: ERMIA as a notation

ERMIA Diagrams as a Notation

You are probably already familiar with the notation of entity-relationship diagrams. A specialised version of ERMIA was developed by Green and Benyon. In a simplified form, ERMIA diagrams look like this:

The syntax requires that:

Every entity in the diagram is connected to every other entity by some path - there are no disconnected subgraphs.
No entity is used more than once.
Every terminal is labelled as optional (open circle) or mandatory (filled circle) and as occurring only once (figure 1) or more than once (letter m).

You don't need to know what the diagram means, but in case you are curious .....

The particular diagram describes the memory system for a fax phone, in which each stored number is a triple consisting of {Name, Voice-phone number, Fax number}. The Directory is a list of these triples, each of which is in its own Location. Notice that the two numbers cannot exist unless they are associated with a Name. Hence, when editing the stored item, the two phone numbers can be edited easily enough, but if the Name is to be changed and you start by rubbing it out, the associated phone numbers are automatically deleted and you have to re-enter them.

Apply the CDs to the ERMIA notation (not to the telephone itself, but the notation we used for describing it). Compare the profile that for TAG and other notations. Consider viscosity, for example - how much work is required if another entity is to be added? Are there any hidden dependencies? Is premature commitment involved? And so on.

Assume that the ERMIA diagram is being created with the use of a simple word processor or drawing packagae.

Note

ERMIA is fully described in:

Green, T. R. G. and Benyon, D. (1996) The skull beneath the skin: entity-relationship models of information artifacts. International Journal of Human-Computer Studies, 44(6) 801-828.

If you want to download it:

Click here for a compressed postscript version (needs gunzip to decompress); 80 K
Or click here for an un-compressed postscript version; 305 K
Or click here for a PDF (Acrobat) version; 121 K