O1 := OUTPUT(PROJECT(base_people_dist,Layout_Person),,'~PROGGUIDE::EXAMPLEDATA::People',OVERWRITE);

O2 := OUTPUT(base_kids_dist,,'~PROGGUIDE::EXAMPLEDATA::Accounts',OVERWRITE);

O3 := OUTPUT(base_combined,,'~PROGGUIDE::EXAMPLEDATA::PeopleAccts',OVERWRITE);

P1 := PARALLEL(O1,O2,O3);

These OUTPUT attribute definitions will write the datasets to disk. They are written as attribute definitions because they will be used in a SEQUENTIAL action. The PARALLEL action attribute simply indicates that all these disk writes can occur "simultaneously" if the optimizer decides it can do that.

The first OUTPUT uses a PROJECT to produce the parent records as a separate file because the data was originally generated into a RECORD structure that contains the nested child DATASET field (Accounts) in preparation for creating the third file. The PROJECT eliminates that empty Accounts field from the output for this dataset.

D1 := DATASET('~PROGGUIDE::EXAMPLEDATA::People',
              {Layout_Person,UNSIGNED8 RecPos{virtual(fileposition)}}, THOR);

D2 := DATASET('~PROGGUIDE::EXAMPLEDATA::Accounts',
              {Layout_Accounts_Link,UNSIGNED8 RecPos{virtual(fileposition)}},THOR);

D3 := DATASET('~PROGGUIDE::EXAMPLEDATA::PeopleAccts',
              {,MAXLENGTH(1000) Layout_Combined,UNSIGNED8 RecPos{virtual(fileposition)}},THOR);

These DATASET declarations are needed to be able to build indexes. The UNSIGNED8 RecPos fields are the virtual fields (they only exist at runtime and not on disk) that are the internal record pointers. They're declared here to be able to reference them in the subsequent INDEX declarations.

I1 := INDEX(D1,{PersonID,RecPos},'~PROGGUIDE::EXAMPLEDATA::KEYS::People.PersonID');

I2 := INDEX(D2,{PersonID,RecPos},'~PROGGUIDE::EXAMPLEDATA::KEYS::Accounts.PersonID');

I3 := INDEX(D3,{PersonID,RecPos},'~PROGGUIDE::EXAMPLEDATA::KEYS::PeopleAccts.PersonID');

B1 := BUILD(I1,OVERWRITE);
B2 := BUILD(I2,OVERWRITE);
B3 := BUILD(I3,OVERWRITE);

P2 := PARALLEL(B1,B2,B3);

These INDEX declarations allow the BUILD actions to use the single-parameter form. Once again, the PARALLEL action attribute indicates the index build may be done all at the same time.

SEQUENTIAL(P1,P2);

This SEQUENTIAL action simply says, "write all the data files to disk, and then build the indexes."