Selection Attributes - Tying an Attribute checkbox value to a spreadsheet
This Attribute type addresses situations where you wish to select one of a large or varying set of enumerated settings. Outwardly similar to a checklist Attribute, the main difference is that the allowed settings for a selection Attribute are not stored in the Attribute itself, but rather in an external spreadsheet file. This not only reduces the amount of data stored in the model, but also allows the set of allowed settings to be easily modified by editing the external spreadsheet—all Attributes that use that definition file will be automatically updated without special handling.
There are a few situations where a selection Attribute cannot be used in place of a checklist:
• When the different selections are not mutually exclusive (i.e., when the checklist can have multiple selections per design element)
• When numeric values or rankings must be assigned to different entries in the checklist
• When the checklist will be used to control other aspects of the eXpress software (such as custom severities, mission phases, checklist-based hierarchical expansions, Attribute-based subsets, or various checklist-based filters and categorizations)
You can use selection Attributes and checklist Attributes interchangeably. There are, however, certain situations when a selection Attribute is particularly useful:
• When the Attribute has a large list of possible values. Because the values are not stored in each instance of the Attribute, model size is reduced.
• When the possible values for the Attribute are expected to change over time. Because the values are stored externally, no global update is needed when a new value is added.
• When you have separate sets of possible values for the same Attribute in different models of a system. This is as simple as selecting a different spreadsheet at each level of the design (there is no need for a single “master” list).
When you first edit the “defaults” for a newly-created selection Attribute, the Attribute Value dialog will appear as in the example at right. Click on the “open” icon and select the Excel spreadsheet file that contains the possible settings that can be selected for that Attribute. Once the definition file has been selected, the possible values for the Attribute (the values in the spreadsheet file) are displayed. The default value is the first value in the spreadsheet.
