Database Management System Emulation - Information Systems Reengineering, Integration and Normalization - page 244

The algorithm of command scanner is:

Begin Get input COMMAND;

Get COMMAND identifier from symbol table;

Compare COMMAND to identifier;

If COMMAND is DML

Then call DML interpreter

Else Begin Verify COMMAND syntax;

If syntax error

THEN return with error

ELSE call METHOD interpreter;

End;

End;

The algorithm of DML interpreter is:

The algorithm of DML interpreter is:
Begin If DML perform data modification
Then begin Query constraint definition for 'BEFORE' action;

While not at end of Constraint definition do

Begin Query Constraint Method;

Execute Constraint Method;

If execution error

Then return with error;

End;

Execute DML command;

If execution error

Then return with error;

Query Constraint definition for 'AFTER' action;

While not at end of Constraint definition do

Begin Query Constraint Method;

Execute Constraint Method;

If execution error

Then return with error;

End

Else Execute DML command;

If execution error

Then return with error

Else return result;

End;