Sequence Diagram

Sequence diagrams are used primarily to understand the time-elapsed interactions between objects (things, actors, phenomae, etc.) in the sequence that those interactions occur.   

In computer science, these diagrams establish a dashed vertical lifeline for every object in the system.  There can be as many as needed to describe all the objects participating in the system.  When an object is active, a narrow rectangle shows the duration that it is “on.”   Perpendicular to the lifelines are arrows denoting some kind of message (a call, a transaction, or other interaction between objects).  Sometimes there are conditions that must be met before an action can continue (e.g. you must show an id, or pay a fee, before acess is granted or an item is received.)

Instructions

Identify all participants: humans, objects, atmospheres, non-human actors, environmental changes - everything that plays a role in shaping interactions on site.  Construct a notation on a roll of paper, in Astah, or Adobe Illustrator.  

When a participant (environment, human, non-human, object) acts, a slender rectangle indicates the start and end of that action. Interactions are drawn with various kinds of arrows to indicate that one object/participant has sent a request, object etc. to another.  Sometimes a request is literally verbal - “please pass the salt”, but it can take different forms - like a gesture,  a non-verbal trigger, a reaction, or an environmental change - “the lights dim”.  Sometimes the recipient of a message reacts (passes the salt).  Sometimes the recipient replies with a message -“I don’t have the salt.”  Sometimes there is no response.  And sometimes there are conditions that must be met before a response is generated to a request.

Questions

What kinds of durations are useful for you to observe?  Seasons, months, weeks, days, hours? Do events repeat, do they remain, do they differ in time?  Do some short-term sequences fit within longer term sequences ?

References

IBM Sequence Diagrams, also here.
Stan Allen, Notations + Diagrams: Mapping the Unmappable.
Lyster, Clare, Landscapes of Exchange.

Possible Tools

Hand Drawing, Adobe Illustrator
Astah free UML software.