A scenario contains a collection of additional information (e.g. temperature, acidity (pH) etc.) and can be attached to other objects (pathway, edge, rule, reaction, compound, model) of the same package. These scenarios naturally have different roles depending on the higher level object. E.g. when attached to a pathway it contains circumstances in a study, when attached to an edge it contains pathway-specific details for a reaction directly connecting a reactant (educt) node with product nodes, or when attached to a rule it contains the conditions when the specific rule applies. But in general, they can be used to annotate any object with a set of arbitrary properties, values and (optional) units.
A list of all available scenarios can be found here: http://envipath.org/scenario. To view all scenarios of a particular package, select the package first, then the scenarios within his package (http://envipath.org/package/<id>/scenario).
First, the user has to create an empty scenario by clicking on Actions and selecting New Scenario for either the default package (http://envipath.org/scenario) or a specific package (http://envipath.org/package/<id>/scenario). Then they enter the name and optionally description and date in the appearing window. The name need not be unique within a package, but making it unique makes the attachment later on much easier. To add properties to an existing scenario the user navigates to that scenario and selects the property to be set from the Actions drop down menu.
Scenarios can be attached to higher level objects from either side, from the scenario with the Attach action and from the higher level object with the Update Scenario action.
To attach scenarios to a reaction shown in a pathway (an edge), the user goes to Edit reaction information on the Pathway page, specifies the reaction (edge) in the pathway, and then selects scenarios for it from those available. In contrast, using the Reaction (Actions->Update scenario) or Scenario (Actions->Attach) pages attaches scenarios to a reaction more generally and not to a specific edge (reaction step) within a specific pathway.