Data membership consistency

Explains the use of the with keyword to ensure data consistency.

The keyword with enables you to indicate that a given element of a tuple must be contained in a given set. If you use it, OPL checks the consistency of the tuple set at run time when initializing the set. The syntax is:

{tupletype} tupleset with cell1 in set1, cell2 in set = ...; 

Let's take an example. You have a set of arcs between nodes. Nodes are defined by a tuple set of tuples consisting of an origin node and a destination node. The with syntax enables you to ensure that the origin and destination nodes do belong to a given set of nodes. Compare Data found inconsistent (keyword with) and Data found consistent (keyword with):

{int} nodes = {1, 5, 7};
 
tuple arc  {
  int origin;
  int destination;
}
 
{arc} arcs2 with origin in nodes, destination in nodes = 
  {<1,4>, <5,7>};
 
execute {
  writeln(arcs2);
};

{int} nodes = {1, 5, 7};
 
tuple arc  {
  int origin;
  int destination;
}
 
{arc} arcs1 with origin in nodes, destination in nodes = 
  {<1,5>, <5,7>};
 
execute {
  writeln(arcs1);
};

If you write Data found inconsistent (keyword with), an error will be raised when the set arcs2 is initialized because the with syntax will detect that the statement

(int) nodes = (1, 5, 7);

is not consistent with the statement

with origin in nodes, destination in nodes = 
  {<1,4>, <5,7>}

If you write Data found consistent (keyword with), the initialization of the set arcs1 will work properly because the with syntax will find that the statement

(int) nodes = (1, 5, 7);

is consistent with the statement

with origin in nodes, destination in nodes = 
  {<1,5>, <5,7>}

tuple node
{
  key int node_id;
  string city;
  string country;  
}

{node} nodes = {<1,"Paris","France">,<5,"Madrid","Spain">, <7,"New York","USA">};
 
tuple arc  {
  node origin;
  node destination;
}
 
{arc} arcs1 with origin in nodes, destination in nodes=...;

execute {
  writeln(arcs1);
};