VDBMS Limitations

Database limitations:

1. Attributes have unique names among all tables in a VDB.

Query language expressiveness limitations:

1. It cannot use the union operation as freely since VDB doesn't allow for repetitive attribute names among tables. E.g.: the enginnerpersonnel(engineerEmpno, engineerName) and otherpersonnel(otherEmpno, otherName) tables in the employee database cannot be joined since they don't return the same set of attributes.
2. It cannot name subqueries (such as attributes, qualified attributes, relations, etc) similar to SQL or relational algebra. So for example, I cannot write: q1 join_{id=id} R because I don't have a way to assign a name to the result of q1.
3. It cannot execute recursive queries such as self-joins due to the naming problem mentioned in (2). E.g.: R join_{id = id} R