The following are POSC's recommendations regarding Epicentre
relational projections:
Projection operations which: 1) faithfully represent the
logical model in a physical schema; and 2) allow for the
implementation of a compatibility layer which completely
hides the effects of the physical implementation from the
logical level are valid. Only operations meeting these
criteria may be applied to a logical subset to create a
physical RDBMS schema.
In a fully POSC compliant data store, Epicentre logical
model rules (full and subset), and rules resulting from the
application of projection operations must be maintained as
meta data in a manner consistent with the requirements of the
corresponding DAEF.
In a POSC compliant data store, valid standard instance
data for the subset of Epicentre represented by the data
store must be maintained.
Data store implementers should build DBMS triggers and
other constructs to enforce POSC data integrity constraints
where practical and indicate which constraints are not
enforced by the DBMS.
To ensure portability of data from an Epicentre subset to
the full Epicentre model and/or other Epicentre subsets,
application developers and/or direct SQL users must take
responsibility for enforcing all data integrity constraints
imposed by logical model rules and projection operations not
enforced, for DAEF users, by the compatibility layer and, for
direct SQL users, by the RDBMS.