Tallis Training

Decisions, Candidates and Arguments: Overview

Decisions: Creating a decision based on results of an enquiry

Decisions are tasks in which a choice is made – either by the Tallis Engine or by the end-user – between several different options, known as candidates. PROforma supports decision-making through a mechanism for generating arguments that may be either for or against a given candidate.

The figure below describes the structure of a decision: candidates are a property of a decision, and arguments are assigned to each candidate.

An argument is defined by two components:

Condition A truth-valued expression that represents the circumstances under which the argument applies (e.g.: blood_pressure < 120).
Support The support that the argument offers the candidate if the condition is true.

The support format can be either symbolic or numeric:
  • Symbolic: the argument can be either for or against the candidate, or it can confirm or exclude the candidate.
  • Numeric: the support is defined using a real value; the argument has a weight assigned to it.

When a decision is enacted, the condition and the support properties are used by the Tallis Engine to determine the effect of each argument and in turn the aggregated effect for a given candidate. The aggregated support of all of a candidate’s arguments is known as netsupport.

A recommendation rule is then used to determine whether or not a particular candidate is recommended. The rule defines an expression that must be true for the candidate to be recommended; this expression typically takes into account the candidate’s netsupport.


  • End-users can select non-recommended candidates if they wish.
  • One or more candidates can be selected if the candidate selection mode of the decision is multiple selection.

Learn more about:

Browse through process-description samples:

If you have installed the Tallis Toolset, you can find these samples in the World > Samples folder in the ACL Web Repository.

See Also

  • Decisions: Creating a decision based on results of an enquiry
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