mkdocs/docs/live/examples/oo2db.etl

// Transforms an object-oriented model
// to a relational database schema
pre {
	var db : new Target!Database;
}

// Transforms a class into a table and 
// a primary key column
rule Class2Table
	transform c : Source!Class 
	to t : Target!Table, pk : Target!Column {
	
	t.name = c.name;	
	t.database = db;
	
	// Fill the details of the primary key 
	// of the table
	pk.name = t.primaryKeyName();
	pk.type = "INT";
	t.columns.add(pk);
	t.primaryKeys.add(pk);
	
	// If the class extends some other class
	// create a foreign key pointing towards
	// the primary key of the parent class
	if (c.`extends`.isDefined()){
		
		var fk : new Target!ForeignKey;
		var childFkCol : new Target!Column;
		var parentFkCol : Target!Column;
		var parentTable : Target!Table;
		
		parentTable ::= c.`extends`;
		parentFkCol = parentTable.primaryKeys.first();
		
		childFkCol.name = parentFkCol.name;
		childFkCol.type = "INT";
		childFkCol.table = t;
		
		fk.database = db;
		fk.parent = parentFkCol;
		fk.child = childFkCol;
		fk.name = c.name + "Extends" + c.`extends`.name;
	}
}

// Transforms a single-valued attribute
// to a column
rule SingleValuedAttribute2Column
	transform a : Source!Attribute
	to c : Target!Column {
	
	guard : not a.isMany
	
	c.name = a.name;
	c.table ::= a.owner;
	c.type = a.type.name.toDbType();
}

// Transforms a multi-valued attribute
// to a table where its values are stored
// and a foreign key 
rule MultiValuedAttribute2Table
	transform a : Source!Attribute
	to t : Target!Table, pkCol : Target!Column, valueCol : Target!Column, 
	   fkCol : Target!Column, fk : Target!ForeignKey {
	
	guard : a.isMany
	
	// The table that stores the values 
	// has an "id" column and a "value" column
	t.name = a.valuesTableName();
	t.database = db;
	
	pkCol.name = "id";
	pkCol.table = t;
	pkCol.type = "INT";
	valueCol.name = "value";
	valueCol.table = t;
	valueCol.type = a.type.name.toDbType();
	
	// Another column is added into the table
	// to link with the "id" column of the 
	// values table
	fkCol.name = a.name + "Id";
	fkCol.table ::= a.owner;
	fkCol.type = "INT";
	
	// The foreign key that connects
	// the two columns is defined
	fk.parent = pkCol;
	fk.child = fkCol;
	fk.database = db;
} 

// Transforms a referecne into a foreign key
rule Reference2ForeignKey
	transform r : Source!Reference
	to fk : Target!ForeignKey, fkCol : Target!Column {
	
	fkCol.table ::= r.type;
	fkCol.name = r.name + "Id";
	fkCol.type = "INT";
	fk.database = db;
	fk.parent = r.owner.equivalent().primaryKeys.first();
	fk.child = fkCol;
	fk.name = r.name;
	
}

operation Target!Table primaryKeyName() : String {
	return self.name.firstToLowerCase() + "Id";
}

operation Source!Attribute valuesTableName() : String {
	return self.owner.name + "_" + self.name.firstToUpperCase() + "Values";
}

operation Any toDbType() : String {
	switch (self) {
		case "String": return "NVARCHAR";
		case "Boolean": return "BIT";
		case "Integer": return "INT";
		case "Real": return "NUMBER";
		default: return "NVARCHAR";
	}
}