Action Description Language - Syntax of ADL

Syntax of ADL

An ADL schema consists of an action name, an optional parameter list and four optional groups of clauses labeled Precond, Add, Delete and Update.

The Precond group is a list of formulae that define the preconditions for the execution of an action. If the set is empty the value "TRUE" is inserted into the group and the preconditions are always evaluated as holding conditions.

The Add and Delete conditions are specified by the Add and Delete groups, respectively. Each group consists of a set of clauses of the forms shown in the left-hand column of the figure 1:

1. The R represents a relation symbol
2. τ₁,...,τ_n represents terms
3. ψ represents a formula
4. The sequence z₁,...,z_k are variable symbols that appear in the terms τ₁,...,τ_n, but not in the parameter list of the action schema
5. x₁,...,x_n are variable symbols that are different from the variables z₁,...,z_n and do not appear in τ₁,...,τ_n, ψ, or the parameter list of the action schema

The Update groups are used to specify the update conditions to change the values of function symbols. An Update group consists of a set of clauses of the forms shown in the left column of the figure 2: